text:
Delete particles in Geometry Nodes based on their position during simulation
I'm working on a project where I need to simulate particles using Blender's old particle system. After the simulation is cached, I want to select a few particles based on their position and delete them from the entire simulation.
To achieve this, I've created a test file with a simple particle simulation where I load the particles into Geometry Nodes using the ParticleInstance node. The particles are created on an object with a single vertex.
The challenge:
I need to delete particles that exceed a certain X position (for example, greater than 3 units) at frame 100 of the simulation.
What I’ve tried:
I’ve attempted using Capture Attribute and Store Named Attribute nodes, but these methods only worked on a per-frame basis, deleting particles in real-time when they met the conditions, rather than for the entire simulation.
Bonus question:
Is ParticleInstance the only method to edit traditional particles in Geometry Nodes, or are there other approaches?
Any advice or help would be greatly appreciated!

For the bonus question: Geometry Nodes can only modify these types of geometry: meshes, curves, point clouds, volumes and instances. No traditional particles from a particle simulation. So I guess the Particle Instance is the only method. But a stupid question: if you want to get rid of "normal" particles that reach a certain X position: why not place a large collision object there that kills particles, eventually to do this at or after frame 100? Or is it mandatory to do this in Geometry Nodes?

@kiwiblending There is no difference between real-time and per-frame basis. I think you are misunderstanding something about that.

@GordonBrinkmann Thanks! Killing particles in one frame by a collision object will distract the viewer in the animation. Maybe I'll write a little more clearly what the project looks like. I have a pool of balls simulated by the Molecular+ addon, through which various 3D models will pass. Sometimes it happens that a particle sticks to the model, it is not always possible to control it during the simulation. That is why I was wondering if it is possible to mark the indexes of these particles, e.g. at the end of the simulation and remove them completely in the entire timeline.

@Lutzi Thanks for the answer. Yes, there is no difference between real-time and per-frame deletion. I must have written it incorrectly, sorry. If I have 10 particles and 3 of them during 100 simulation frames exceed position 3 in the X axis, I would like to delete them for the entire simulation. So that after the deletion process there are only 7 particles in the first frame. This way I will avoid troublesome simulation moments and I will not have to delete them in real time.

Of course if a condition is first met on frame 100, a Capture Attribute or something similar cannot store the information on frames 1 to 99, because the animation is not running backwards. I guess there is no easy way to do this, you would basically have to read the positions of all particles on frame 100 while you are still on frame 1 and delete all by index which will meet the kill condition on frame 100. So if someone knows a way how to access location data of frame 100 on frame 1, this might help - but I'm not that someone.

Maybe I need to duplicate the object with particles, apply simulation in a given frame and then transfer this information to geometry nodes tree removing the particles? Will try it later.


text:
Is it possible to automatically move other strips while dragging another strip?
Imagine you click a drag a strip on the sequencer. When the strip comes in contact with another strip I think it would be useful if the stationary strip would adjust around the influence of the strip I'm dragging. Perhaps swapping places, for instance.
Another automatic adjustment I wonder about is when adjusting after making a knife cut and grabbing one of cross sections. Then when I drag that handle, if I move it as if to overlap the intersection, then the other strip would adjust it's length to compensate as you move it.
It seems at some point I saw an option for it, but I can't remember the name for it. The word "scrobble" comes to mind, but I've found nothing about it. I have a strange memory. Thanks!

This question appears to be off-topic because it is a feature request and not an actual question. These should be reported to Blender's tracker instead.

@Polosson  I don't see it as a feature request.  He's asking if it is possible, not requesting that the feature be added.

Nowadays you can slide your strips if that helps...

@Samoth Similar to my description?

Well, it's possible. You can use the "Expand to fit" option which is enabled by hitting G for grab and then you can hit G again to toggle "Expand to fit" permanently or hold down ALT to use toggle it temporarily.
When you have three strips with the new one selected but not yet in your final row:

Just hit G to grab and then G again and place it "over" the existing strips:

Confirm with left mouse button (LMB) or Enter and there you have the strip inserted in between the two existing ones:

And to answer your second question: Just snap the handle next to the other strips one with dragging it and holding down Ctrl. Then just Shift-select the other handle and slide both of them with G.
Moving a single handle works with expand to fit as well (even though, the next strip is then moved and not trimmed in length).
Finally you can use Alt+Left Arrow/Right Arrow to swap two adjacent strips.

This works well enough. Thank you for your time and effort that was put into this well thought out post.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
delete bone constraint in python
I have a quick and dirty script to change the constraint settings for the bones of an armature:
import bpy

for bone in bpy.context.selected_pose_bones:
    try:
        bone.constraints[0].target_space='LOCAL'
        bone.constraints[0].owner_space='LOCAL'
        for cons in bone.constraints:
            if cons.type == 'COPY_LOCATION':
                WHAT GOES HERE TO DELETE THE CONSTRAINT?
    except IndexError:
        pass

As you can see I also want to delete any Copy Location constraints on the bones and can't figure out how. Manually deleting generates, bpy.ops.constraint.delete() in the Info window, but adding that to the script gives me a "context is incorrect" error.

Here's a way to achieve this without the Try-Except block:
import bpy

for bone in bpy.context.selected_pose_bones:
    # Create a list of all the copy location constraints on this bone
    copyLocConstraints = [ c for c in bone.constraints if c.type == 'COPY_LOCATION' ]

    # Iterate over all the bone's copy location constraints and delete them all
    for c in copyLocConstraints:
        bone.constraints.remove( c ) # Remove constraint

On a more general note, the remove method is very common in blender collections, so when you try to delete a member of a collection always have a go at this in the console:
bpy.data.materials.remove( myMaterial )
bpy.context.object.modifiers.remove( someModifier )

Also note that this method usually takes the actual element reference (modifier object, constraint object, etc) as a parameter, not an index.

Apply and Delete.
import bpy

for bone in bpy.context.selected_pose_bones:
    for c in bone.constraints[:]:
        if c.type == "COPY_LOCATION":
            bpy.ops.constraint.apply( constraint=c.name, owner="BONE" )

Please edit your answer to correctly format it. It's currently unusable as is.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Delete object by location
How can I do something like,
bpy.ops.object.select(object at location x,y,z)
bpy.ops.object.delete()

In the event you want to include some objects whose origin points are close but not exactly the location given. Please note this does not specify object type so any object (camera, armature, light, etc) within range will be deleted.
import bpy
from mathutils import Vector

target_loc = (1.0,1.0,1.0)
target_deviation = .1

objs = [obj for obj in bpy.data.objects if (
        (obj.location[0]-target_loc[0])**2 +
        (obj.location[1]-target_loc[1])**2 +
        (obj.location[2]-target_loc[2])**2 <= target_deviation**2)]

bpy.ops.object.select_all(action = 'DESELECT')
for obj in objs:
    obj.select = True
bpy.ops.object.delete()

I think this should be the way, even if you're looking for objects at the locations (using a tiny epsilon / deviation). Just to smear out floating-point errors.

Floating point errors is something I immediately thought when I saw the question as well, but I could not make them manifest themselves when testing. If I move an object randomly and then just copy the values from Blender's input fields it seems to work. I think they may become an issue, but not necessarily are an issue in all cases.

I can be precise in my location because I'm removing objects I have placed whose location is recorded in a list of tuples. My focus is the list however, not the object, so my script is manipulating the tuples and then adding/removing objects at those locations. The issue therefore, is not whether there's an object there (I already know that), but how to issue the command, delete the object at the known location.

@d8sconz I think floating point errors may be an issue in your described scenario. They occur because of the way values are stored in computer memory so it depends on what you are doing with those numbers and this answer can be very useful if those errors did become a problem at some point.

There is no need for the euclidean formula when there is a vector API  use the length, magnitude or length_squared property of the vector result of subtracting one location from another.   Would only involve v = Vector(target_loc) to convert tuple to vector in code above.

Vector maths
Blender uses vectors. The object's location is a point in 3D space designated by a mathutils.Vector.
Its local location relative to it's parent
lloc = ob.location

Its global location, relative to the global origin (0, 0, 0)
gloc = ob.matrix_world.to_translation()

If we have a point in space (global) P then the distance from the point to the object is the length of the vector gloc - P.
d = (gloc - P).length

If this distance is within some radius d, then we select.   Setting this to a very small value, 1e-7 is around blender's error margin, and for most applications can be considered the same location.
Relying on equality of vectors v1 == v2 is IMO not reliable.
>>> Vector((0.9999999, 1, 1)) == Vector((1, 1, 1))
False
>>> Vector((1.0000001 , 1, 1)) == Vector((1, 1, 1))
True
>>> Vector((1.0000002 , 1, 1)) == Vector((1, 1, 1))
False

Test script, selects any object within d of scene cursor.
import bpy

context = bpy.context
d = 0.0001

loc = context.scene.cursor_location

for o in context.scene.objects:
    gloc = o.matrix_world.to_translation()
    # o.select = (gloc - loc).length < d # pre 2.80
    o.select_set((gloc - loc).length < d)

Since there is a chance the active object is not selected we'll set it to None before calling the delete op
# context.scene.objects.active # for pre 2.80
context.view_layer.objects.active = None
bpy.ops.object.delete()

Vector((0.9999999, 1, 1)) == Vector((1, 1, 1)) returning False is completely correct. Vector((0.99999999, 1, 1)) == Vector((1, 1, 1)) returning True isn't.

I think one loop is enough for this:
import bpy
from mathutils import Vector

location = Vector((0,0,0)) # this should be some location

for o in bpy.context.scene.objects:
    if o.location == location:
        bpy.data.objects.remove(o)

Obviously all kinds of conditions related to the location could be checked, but those should be another questions.
I think keeping in mind that floating point binary conversion errors do exist is a good idea in this context as well.

I'm trying to get my head around why any loop is needed. I have objects in known locations so I don't (in my mind) need to loop through all the objects to find if it's there. Are you saying that something like, bpy.data.objects.remove(o.location), is not possible?

You only have objects that have the property of location. The space has no properties, you do not work with it in any way, so you cannot check what objects belong to what space, but only the other way around - what objects have that location in space. I don't know if what I am saying is making a lot of sense, but anyway, you can only do it checking all the objects you have. Only they are defined in Blender.

Using equality to test floating points is an issue, see example in my answer.

I think it can be and is likely to be. It not necessarily is in all cases.

I think let's just cross that bridge when we come to it. There is no reason to assume that it definitely is a problem in this case. We don't know the wider context.

In the wider context of wanting 0.99999999999999999999999999 being treated as 1, don't use equality when testing floats.

In all contexts that do not involve binary rounding errors, always test floats with equality. :D If I only store or assign the location without computing anything, and then need to test, what objects end up having it, there is no point for me to write unnecessary code.

You will have to loop trough all the objects in the scene and check its location. Then you can delete that obtained object if one is found.
import bpy
from mathutils import Vector

x = 0
y = 0
z = 0

objects = [ o for o in bpy.data.objects if o.location == Vector((x,y,z))]

if len(objects) > 0:
    for o in objects:
        bpy.ops.object.select_all(action='DESELECT')
        bpy.data.objects[o.name].select = True
        bpy.ops.object.delete()

Extension for multiple objects and multiple possible locations
import bpy
from mathutils import Vector

locations = [Vector((0,0,0)), Vector((4,0,0))]

objects = [ o for o in bpy.data.objects if o.location in locations]

if len(objects) > 0:
    for o in objects:
        bpy.ops.object.select_all(action='DESELECT')
        bpy.data.objects[o.name].select = True
        bpy.ops.object.delete()

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Given location(x,y,z), check if object exists at that position
As the title says, I want to be able to check a location for the existence of an object. I'm randomly filling a space with objects and want to make sure I'm not placing an object somewhere that is already occupied. Current code is:
for x in range(1000):
    loc = np.random.randint(-100, 100, 3)
    bpy.ops.mesh.primitive_cube_add(size=2, view_align=False, enter_editmode=False, location=(loc[0],loc[1],loc[2]))
    bpy.ops.wm.redraw_timer(type='DRAW_WIN_SWAP', iterations=1)

I'd like to add something like,
if NOT location(loc[0],loc[1],loc[2]):
    add object...

Existing questions seem to be about getting location of known objects. I need the reverse of that - getting an object (or not) at a known location.

Related  Fills a box with randomly generated spheres.

Actually the reverse of what I'm after. It queries position of known spheres where as I want to query known position for an object.

Huh?  in the script  I'm randomly filling a space with objects and want to make sure I'm not placing an object somewhere that is already occupied Each new sphere has to be positioned using its own "known position" against the "known position" of others.   Yes the objects are known to be spheroids with origin at geometry, and positioned globally. The others could be scene.objects ie all other objects in scene.  The test could involve the overlapping of bounding box  etc.

As a work around I'm appending each cubes location to a list of tuples as they get added to the scene. Each new random location is then tested against that list. My question is, do I have to make my own list like this. I can query scene.objects, but I have to turn the locations into a new list on each iteration. Or do I.

As in example shown would iIMO be far better off using vectors. The location is already a vector. If the length of the difference of two vectors is less than some tolerance it is considered same. Whereas is (0.999999,) == (1,)   It places a new sphere in a location that is available. There is a "tweak" to edge them away from the other if slightly overlapping. All this is simplest with spheres.  The beauty of scripts is you can run them to see how they work. I've updated the code to also work in 2.8 if you are using that version, which I would suggest you do if you are just starting.

If purely creating the random objects...
Here is a test script that places 100 cubes  in scene with integer location components x, y, z selected randomly from range [-10, 10]
Each random location could be added to a list or set when assigned and its contents checked x in [0, 1, 2] Instead I've chosen to use  defaultdict(list), which behaves like a dictionary that returns an empty list() if there is no value for that key.   An empty list is Boolean False ie there is no object in that location..
>>> dd = defaultdict(list)
>>> dd["missing"]
[]

The tuple (x, y, z) is used as a key.    If the key is taken, choose another random number combo, otherwise append to the list of that key marking as taken,  until all cubes placed.
import bpy
import numpy as np
from collections import defaultdict

ncubes = 100
locations = defaultdict(list)
i = 0
while i < ncubes:
    loc = tuple(np.random.randint(-10, 10, 3))
    if locations[loc]:
        continue

    locations[loc].append(i)
    bpy.ops.mesh.primitive_cube_add(location=loc)
    i += 1

Without checking against already existing objects in a scene this is pretty much purely a python problem. A good place to find answers to python questions is https://stackoverflow.com


text:
Is it possible to convert the dimensions that MeasureIt gives into text or mesh for manipulation?
In reality I would like to create dimensions on objects and output the image in Panorama to read in a 360 reading engine.
So I am thinking if it is possible to convert the dimensions into text it would be possible, I had tried to create a script for this, but I encountered problems when the dimension comes it is attached to the world center of Blender.

This is exactly what I want. A quote that will be considered as an object, and that can be manipulated as desired. Too bad the gentleman doesn't want to tell me how he did it to obtain this result.

What image? What panorama? What is 360 reading engine?

You could make a mesh that consists of a single edge(or whatever else that has something with any coordinates and you can move that - could be two verts, could be single vert and object's origin - whatever). We have the coordinates in Geometry Nodes. You can see them if you enable Viewer Node's Attribute Text overlay:

So we have coordinates of vertex one and vertex two. Or as one would say in Nerd: that's vertex 0 and vertex 1. So one can sample the position of those verts with index 0 and 1 and Vector Math node even has Distance mode so there is no need to do any math at all - how good is that?..

All that's left to do is to convert that into text and place it somewhere:

And that's how you have a measurement apparatus constructed with geometry nodes. You can duplicate it easily and snap vertices anywhere.

You can of course place the text anywhere you want and make whatever additional geometry that may help indicate what is measured. You don't need to use the geometry of the object the modifier is on, you could sample another object with the use of Object Info node as well. The possibilities are pretty much endless.

waooh amazing, thank. but is not totaly solve my request. I share my script, can you please cket it for me ?

You got two answers as far. Why didn't they work for you?

how to explain it? for example your method is very practical, but it does not allow me for example to have the possibility of rotating the text without really moving the line to which it is attached. I would actually like to have the possibility of putting the text according to the angle of view that I take in order to read the dimension, so if there was a node that I can add to have this option it would be good. also I would like to have at the ends of the dimension line arrows at both ends. and also if possible, a way to dimension the angles

"but it does not allow me for example to have the possibility of rotating the text without really moving the line to which it is attached" - It absolutely lets you do that and whatever else you may want or imagine! I just don't know what you want to do so I provided a simple example. Maybe add a specific example(an image or a sketch) of the result you want in your question so it's possible to provide more specific answers.

This script, from Blender Artists worked when I ran it but it has its limitations.
import bpy
from mathutils import *

with open("C:/Users/...YOUR PATH/Desktop/measureit_output.txt", mode="w") as f:

    objects = bpy.data.objects.items()

    for obj in objects:
        mg = obj[1].get('MeasureGenerator')
        if mg:
            obj_name = obj[0]
            for e in mg[0].items():
                if e[0] == 'measureit_segments':
                    ms = e[1]
                    for m in ms:
                        measure_name = m.get('gltxt')
                        measure_points = (m.get('glpointa'), m.get('glpointb'))

                        vdata = obj[1].data.vertices
                        a = vdata[measure_points[0]].co
                        b = vdata[measure_points[1]].co
                        length = (a - b).length
                        print(f"{obj_name};{measure_name};{length:.2f}")
                        f.write(f"{obj_name};{measure_name};{length:.2f}\n")
            print()

Limitations
As I said it has limitations which I can't adequately bug test.
It seems to work fine for measurements inside objects, but does not output the distances between between objects or the objects and the origin correctly when I use 'Link' or 'Origin'.
The output.txt file looked like this, notice the last figure is incorrect and does not match with my image:
Cube;Ymeasure;2.00
Cube;Zmeasure;2.00
Cube;Xmeasure;2.00
Suzanne;Xmeasure;1.64
Suzanne;Suzanne-Cube;1.39
A workaround might be creating an object for your measurement such as a simple mesh line.

Perhaps this was part of your approach already.  It may help to show people what you have already tried (python, .blend) in order to save time and get a better result.

I have the script, can you tell me how to share it?

People generally would ask a python tagged question, then just write it in their question, or attach it.  This is a useful site for uploading blend files to Stack Exchange- https://blend-exchange.com/


text:
quick effect animation render doesnt show the smoke, but the image render and preview do. (EEVEE)
My simulation is quick effect: fire and smoke, in eevee it has a particle system driving the inflow, and resolution was set to 64. I baked the simulation and particles but when I rendered the animation (250 frames) the  smoke does not appear. In render preview and image render it shows up. When I render one frame it shows up. When render ing less frames, about 20 it just becomes a blob that shakes. This is in blender 4.3. I am using a principaled volume for shading. The shorter animation results in a volumetric square that jitters but does not follow the baked animation. The domain has location, scale, and rotation applied. The animation works correctly in an image, but not in the animation. I am using the FFmpeg video format.

Hello and welcome. Rather than take photos of your monitor post actual screenshots instead, see How to take a screenshot. Photos are harder to read because we have to look past external interferences (like reflections, smudges or Moiré patterns) and guess if we are looking at hardware issues such as a malfunctioning display or connections, a software level issue like driver malfunction or glitch, or actual artifacts or issues with the model itself.


text:
Close gaps / move mesh islands in a grid after scaling elements (geonodes)
I want to create a simple wall (or cobbled path, or something with blocks) with different block sizes. One way I've been thinking of doing this is to start with a grid, split the edges and scale the elements (there are a few examples of this, which use triangulation and dual mesh too).  This creates the following (quite obviously!):

Is there a way after doing this that I can move each mesh island along any particular axis (in this case 'Y') so that the gaps are closed?  I have tried various ways using ray casting, or trying to capture position attribute of each island... but unfortunately my understanding of geonodes is nowhere near good enough to work out how to do it.
I understand that there might be different ways of getting the desired results (many many ways I am sure), but I would be particularly interested in understanding how to work with mesh islands and being able to manipulate them on an individual basis.

Same problem as solved by me in the (wrong) answer here: Geometry Nodes: Translate each instance by bounding box dimension

Is this what you want?

@DanyaK That is exactly what I want (I know there is a way to stack with Accumulate Fields - but did you do this with moving mesh islands about?). Thanks.

I actually just moved the faces and not the islands, which I assume is not what you want. Do you need a solution that works with complex 3D shapes and isn't limited to just squares?

@DanyaK I think that would probably work - I'm only using squares,

Just for clarification: would you like a solution WITHOUT Accumulate Field  node ?

@StefLAncien Not necessarily, no.  Anything that works is good for me (I'm about to try to solutions I've been given).  Thanks

The solution I'm going to show only works if your objects are assumed to be single face objects, otherwise it will give the wrong result. The solution looks like this:

The idea here is to use the Accumulate Field node:

First of all, you simply find the freed space for each square after resizing them.

Then you use the Accumulate Field node. It will sum up the spaces, since that's the offset each square needs to be moved.

The accumulation needs to happen for each column, so I use integer division to group the faces correctly:

Now just use that node. I negate the value at the end, since I need to move each square back by the amount of space produced.

Overall, I think the solution is similar to what was suggested in the comments above. This is just a simplified version, as it is used for a simplified case. If you are not satisfied with this, then be sure to also check out the proposed solution. It also explains why the Mix node is used after the Accumulate Field.
Or you can wait until someone else comes up with a more advanced solution.

Thanks - this worked well. Many thanks


text:
How to make hair so blurry and soft?

The screenshot was from an anime, I'm sure it was made by Blender, and it looked like only the hair was so blurry and soft

Hello, maybe it's a blur effect made with the Compositor?


text:
Animations on char do not work - stays in t-pose
I am separately importing a model and an animation (both FBX; the model is originally in t-pose and the animation is an idle animation) and then remove the armature from the imported animation. Then in Animation -> Action Editor I select the imported animation.
I see that the imported models armature moves, but the movement seems relative to the models t-pose. For example the arms are moving slightly, but instead of hanging down they are stretched to the side.
I used the same procedure on other models and animations and the animations work as expected. When changing the animation in the Action Editor the model immediatelly changes its posture to the first frame of the animation. So I am not sure, why the procedure works with some models/animations and not with others.
I am new to blender and am very likely missing some setting either for the imported model or the imported animation.
Any tips and hints on how to reliably combine imported models and animations would be greatly appreciated!
Thanks in advance for any help and best regards,
Patrick

I do recommend you edit in screenshots of what you’re talking about, it’s usually expected as details for the sort of thing. It’s probably why your question got downvoted.

As far as I can tell, this is expected behavior. Animations store bone pose transforms relative to their absolute starting point (where they were placed in edit mode, where they end up if you zero the transforms in pose mode), so if you put an animation on an armature where the absolute starting transform of the bone is different, it will look incorrect. There are, however, addons and tutorials for retargeting animations to new skeletons, as this is a common need for motion capture. I recommend you look into that.


text:
How to place an IK pole target bone when IK chain is not aligned to cardinal axes
I have a bone chain I would like to create an IK system on, but the chain is not flat on one of the cardinal axes (global x/y/z). How can I add a pole target bone to this chain without manually aligning the bones to the cardinal axes? For example, my character is imported with a chain in A-pose, but a T-pose would be better aligned.

To find a position to place the IK's pole target bone, one must do some basic vector math based on the existing bone chain.
Suppose you have a bone chain for an arm; one point is the shoulder; next, the elbow; lastly, the wrist. Using these three points, we can define a plane on which to create a new bone to act as the pole target. Using a point on this plane means the chain will not move when we add pole target influence to the IK constraint.
The first step in setting up an IK chain in this fashion is aligning bone rolls with Blender's built-in roll calculator (shortcut ctrl-n in bone edit mode). With correctly rolled bones, the IK solver behaves predictably, always pointing the chain at the pole target.
The second step is to find the plane defined by the three points in the bone chain. We can easily find a reasonable place to put a bone with the code snippet below.
Step three involves more vector math to find the proper pole angle for the IK constraint. This angle is important because it allows the rigger to create an offset between the bone chain's orientation and the pole target's direction. Using the right pole angle makes animating and rigging more visually intuitive. The code snippet below includes a segment to calculate and plug in the proper pole angle for the IK constraint.
Lastly, I included a segment to create the IK constraint and plug in the necessary bones and numbers. This makes the script a one-button step to create an IK from just shoulder, elbow and wrist bones.
Some Notes:

You will need to fill in the names of the bones and armature object you would like to use at the top of the script. Make sure these are the bones you want to use!
The IK target (not the pole target) must not be a child bone of the chain you are putting the IK constraint on.
Run this script from Blender's text editor.

Snippet:
import bpy
from math import degrees
from mathutils import *

# Set names here:
arm_name  = "Armature"
bone1     = "shoulder"
bone2     = "elbow"
ik_target = "ik.target"
pole_name = "ik.pole"

########################################
# Create and place IK pole target bone #
#          by Marco Giordano           #
########################################

bpy.ops.object.mode_set(mode='EDIT', toggle=False)

# Get points to define the plane on which to put the pole target
arm_obj = bpy.data.objects[arm_name]
arm_edit_bones = arm_obj.data.edit_bones
A = arm_edit_bones[bone1].head
B = arm_edit_bones[bone2].head
C = arm_edit_bones[bone2].tail

# Vector of chain root (shoulder) to chain tip (wrist)
AC = C - A

# Vector of chain root (shoulder) to second bone's head (elbow)
AB = B - A

# Multiply the two vectors to get the dot product
dot_prod = AB * AC

# Find the point on the vector AC projected from point B
proj = dot_prod / AC.length

# Normalize AC vector to keep it a reasonable magnitude
start_end_norm = AC.normalized()

# Project an arrow from AC projection point to point B
proj_vec  = start_end_norm * proj
arrow_vec = AB - proj_vec

# Place pole target at a reasonable distance from the chain
arrow_vec *= 2.0
final_vec = arrow_vec + B

# Add pole target bone and place it in the scene pointed to Z+
bpy.ops.armature.bone_primitive_add(name=pole_name)
arm_edit_bones[pole_name].head = final_vec
arm_edit_bones[pole_name].tail = final_vec + Vector((0.0, 0.5, 0.0))

# Enter Pose Mode to set up data for pole angle
bpy.ops.object.mode_set(mode='POSE', toggle=False)

##############
# Pole Angle #
# by Jerryno #
##############

def signed_angle(vector_u, vector_v, normal):
    # Normal specifies orientation
    angle = vector_u.angle(vector_v)
    if vector_u.cross(vector_v).angle(normal) < 1:
        angle = -angle
    return angle

def get_pole_angle(base_bone, ik_bone, pole_location):
    pole_normal = (ik_bone.tail - base_bone.head).cross(pole_location - base_bone.head)
    projected_pole_axis = pole_normal.cross(base_bone.tail - base_bone.head)
    return signed_angle(base_bone.x_axis, projected_pole_axis, base_bone.tail - base_bone.head)

base_bone = arm_obj.pose.bones[bone1]
ik_bone   = arm_obj.pose.bones[bone2]
pole_bone = arm_obj.pose.bones[pole_name]

pole_angle_in_radians = get_pole_angle(
    base_bone,
    ik_bone,
    pole_bone.matrix.translation)

print("Pole angle: {}".format(degrees(pole_angle_in_radians)))

#####################
# Add IK Constraint #
#####################

# Bone constraints are added in Pose Mode
bpy.ops.object.mode_set(mode='POSE', toggle=False)

# Add IK constraint
IK = arm_obj.pose.bones[bone2].constraints.new('IK')

# Set IK parameters
IK.target = arm_obj
IK.subtarget = arm_obj.pose.bones[ik_target].name
IK.pole_target = arm_obj
IK.pole_subtarget = arm_obj.pose.bones[pole_name].name
# Pole angle is set with radians, despite displaying as degrees in the UI
IK.pole_angle = pole_angle_in_radians

Pole angle: Jerryno
Vector math: Marco Giordano


text:
How to change scale of a texture through nodes
I have created a wave texture which I assigned to one face, this is the object rendered:

This is the node setup:

I have set the wave type to be "rings", but in the rendered object these rings are stretched out like ovals.
How can I scale the texture in one axis to get circular rings?

The stretching you are seeing is because the wave texture uses Generated texture coordinates by default.  Generated coordinates are based on the bounding box of the object.  So if the bounding box is not a cube (which yours isn't), the generated coordinates will be stretched.
You can fix this by using Position texture coordinates.  Position coordinates are based on world-space, so they are not affected by the scale and bounding box shape of the object.
See this answer for more on generated vs. position coordinates.


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ALT + SELECT in edit mode selects whole mesh instead of edge loop
I have a grid which looks like this:

The problem is, when i try to use ALT + SELECT in order to select one edge loop, it instead selects the whole mesh.
How can i  fix this?

Loops can't be selected with Alt+Right click without faces. You can select all A, and make faces with F, then you'll be able to select loops.


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How to grid-fill a spiral
In my newest project I've made a line spiraling downwards in the shape of a sphere, as seen below:

You can also see how I started to fill the gaps with faces, this was done by manually picking every edge and adding a face.
So I was wondering: is there any other way to quickly fill all the gaps?
Thanks for reading!

I think the F2 addon (comes with Blender) should do this.

There is an addon called F2 (comes bundled with Blender by default) which could speed this up.
To enable the addon go to File > User Preferences > Addons (or Ctrl+Alt+U) and search for F2 and enable it.

Once enabled, this addon adds two new functions to the F key, one of which should speed up your workflow considerably (the other is described here).  Just create the first face of the spiral, then select the inside edge of the new face and hit F to create a new face along the spiral.  Then keep pressing F until you have filled the spiral.

Thanks so much! People like you are the reason I love this community. Just curious though, how do you make those .GIFs? Again, thanks for taking your time :)

@EspenSales See this meta post on GIFs.  (If this answer has suffeciently solved your problem you can mark it as accepted by clicking the checkmark under the voting buttons.)


text:
Strange lights appearing
I just recently rendered this scene:

My problems is the bright spot on the bottom-right corner. The same kind of light can be seen along the cave-wall to the right.
Here's the .blend file if you wanna take a look
Thanks for any answers!

I took a quick look at your blend. It does not seem to match the render you posted. There are substantial differences in the green crystal and the stalagmite/stalactite pillar near the entrance, not to mention differences in the placement of the mushrooms. Have I made a mistake, or was there another version of the blend you could post?

Sorry about that, I must have forgotten some setting on and saved. The .blend I provided will still catch those highlights, though. I'm gonna test around the sun lamp as suggested by @PaulMc.

The blend file that you have provided doesn't render to the image above.  It is always a good idea to pack external files into the Blend file.  However, my guess would be the sun lamp you have in there is managing to reach that part of the scene and provide some highlights on the surfaces you are getting the bright spots on.  A quick test would be to turn off the sun and see if the bright spots remain.  If they go away then you can be sure that the sun is the source.  If you still want the bright area at the rear of the scene then you may need to rotate the sun a little or change it to a point source and add a Color/Light Falloff node into the strength.

Turns out the sun lamp was the culprit. It also didn't make the scene look any better than without it, from the two renders with and without... so goodbye sun! Thanks for the help :) (that's for you, not the sun)

If this answer solved your problem feel free to 'accept' this answer by clicking the checkmark on the left. See: http://meta.stackexchange.com/questions/5234/how-does-accepting-an-answer-work for more information.


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How to divide a circle into slices for each side
Sorry if the terms I used are incorrect, but I was wondering how I can divide a circle into several triangles, one for each side of the circle, as well as subdivinding those into quadgons like so:

I made the example on the left by hand (selecting each vertex and adding a face) which took way too long, and would clearly take too much time to do with other more complex circles.
I tried using subdivide and loop cut and slide, to no avail. So how can I do this quickly?

You can find a possible answer in this related question:http://blender.stackexchange.com/questions/39289/why-cant-i-loop-cut-a-cone.

There are several approaches.
Adding rings
If you have a circle that is a triangle fan and you want to give it rings, just Circle Select C the edges that make up the "spokes" of the circle, Esc out of Circle Selection, and Subdivide W > "Subdivide".

In the Operator Panel on the left you can adjust the number of subdivisions.

Creating a triangle fan
If you don't yet have a triangle fan and need to create one, select the edge loop of your circle, Extrude E, then Scale S inward. Type "0" to scale in to the absolute center, Enter to commit. Remove doubles W > "Remove Doubles".

Note that the face normals may not be pointing in the direction you want. In the GIF above this is evident from the dark shading. You can remedy this by selecting the faces of your circle and pressing W > "Flip Normals".
Starting with a triangle fan
When you create your circle there is an option for Fill Type. Set it to Triangle Fan and you will already have a circle made up of tris.

Insetting
A less common approach, but good to know about.
If you have a circle that is an n-gon, with the face selected, press I and you can inset it inward. Finally, Scale S in to "0" and Remove Doubles W > "Remove Doubles".

Beveling the center vertex
If you're starting from a triangle fan, one more approach you can take is to bevel the center vertex to create the edge ring necessary to perform a Loop Cut. If you type in a near-zero value the 8 resulting center verts will be right on top of each other and you can easily patch the center hole later using Remove Doubles.

I would delete the "Triangle fan" approach as the OP is asking for "subdividing in quadgons". I also find that Adding Rings is the most suitable answer for this question as it requires to run the command only once even if you want multiple rings: I would put it on the top.

@Carlo Yeah, I definitely use the adding rings approach most frequently. I was going for an order-of-operations approach, as in, if you start with a triangle fan there's no need to make one. But I agree adding rings is the most relevant. Currently adding screen shots. I will reshuffle the order. thanks for the feedback.

@Carlo I was wondering how to both fill with triangle fan and subdividing into rings, so Mentalist don't take any of the methods away!

I'm trying the Extrude and Scale method, but I don't know how to effectively remove the doubles, how do I do this?

Ok! Do as if I said nothing. (in this case was better your previus order :P) Sorry!

Don't sweat it! :D

@Mentalist i didn't notice that you showed how to remove doubles in the animation, problem solved!

@EspenSales Glad it worked out for ya! Happy Blending.

@Mentalist turns out it didn't work, simply that nothing happens when i press Ctrl-D, know any remedies?

ok ok forget it I managed to do it :P finally! XD

Using a Spin Tool.
Add a Circle with a triangle fan and subdivide (W-->Subdivide) one of its edge as many times as you like. Select the non-selected vertices (Ctrl+I) and delete them (X). Go to the Tool Shelf (T) on the left and press the Spin button located in the Tool bookmark. Then adjust the spin settings and remove doubles (with the whole mesh selected press W-->Remove Doubles).

Adding the loop cuts.
Add a Circle with no fill. Select all the vertices (A),extude them (press E), scale (press S) and input a very low value (like 0.0001) from your numerical keyboard. Now press Ctrl+R to add some loopcuts. Use a mouse wheel to set the number of the cuts. Deselect everything (A), then select the vertices in the middle (use a border select B) and merge them at cursor (W-->Merge-->At Cursor).

Neat! Don't know If I'll be using it so much, but knowledge is power! Thanks

Actually this method would have saved me alot of time if I were to use it on what I'm working on...

The merge option is also new to me, thanks for the info!


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How to apply a square mesh to every face of another object?
I'm, sure there's a feature for this, but I don't know the name or how to search for it. basically I want to recreate the ceiling of the pantheon:

I was thinking I could make a half-sphere, and then on another object I make a square stepped-pyramid shape, and then somehow "apply" that shape to selected faces of the sphere to take into account the narrowing of the squares... Any suggestions for a workflow like this?

Tissue addon is made for that. It is included in Blender, just activate it. You'll find it in the tools, right of the 3d view. Then tessellate onto the half sphere (active object) with the wall part object (selected).

a link to the documentation https://docs.blender.org/manual/en/latest/addons/mesh/tissue.html


text:
Retopology Clothing After Knife Project
I'm working on modeling some clothing in Blender using the SimplyCloth plugin. To actually create the mesh itself, I'm using the technique of starting with a 100cm x 100cm plane, subdividing it into a 100x100 grid so I can get my measurements, and UV mapping it and applying a fabric material so I can make it look like each pieces were cut from one original piece of cloth.
I've used this technique before on a simple loose-fitting shirt made entirely of square pieces, which works quite well. However, I'm now making something that has a more complex, fitted shape.
I created a pattern to the correct shape, and then used Knife Project against my grid to "cut out" the pieces of fabric. This is the resulting topology:

Obviously I have issues now with triangles and N-Gons that will need to be cleaned up for good topology. Subdividing (so each grid is .5cm instead of 1cm) would held in some places, but not all. Any recommendations for how to proceed with this before I start trying to sew everything together?

The more important issue is not topology for your render-- quads, etc-- but topology for your cloth physics, which will bend only along your edges.  If you've been happy so far with your results, I don't expect you'll be any less happy with this, with or without ngon edges.  But, if you're concerned, the quickest way to retopo this will be a decent remesher.  Exoside Quad Remesher costs (like fifty bucks I think) but it will handle this task just fine and all you have to do is hit one button.  Not sure how Instamesh, free but second best IMO, will handle it.

Ideally these will become assets in a game, so it will be important beyond just the physics.

Then you'll want to retopologize after the physics.  Good topology follows the lines of the shape.

Then I'll need a way to retopologize while preserving the UV maps. The built-in Remesh modifier destroys the maps in the process. Retopologizing and UV mapping after the physics will throw all of that off.

There is no such thing as retopologizing while preserving UV maps, regardless of when you do it.  If you want good topo from bad topo, you won't be preserving UV maps, it's one or the other.  But for these simple, undistorted, unseamed cuts of planes, data transferring UV from a pre-retopo copy should be fine.

Yes, but won't retopo change the number of vertices? UV data can't be transferred if the geometry changes.

Transfer from nearest face interpolated.  Using a data transfer modifier.

Ok, that got the mapping. Between Black Fox and your comments I think I have a way forward.

Edit, my old answer didn't work, here is my revised method:
Add a solidify modifier to your plane to give it some thickness,
Add a remesh modifier after the solidify modifier. I'm using "Sharp" with the settings you can see below. This prevents N-gons and gives you a starting point.

If you need more resolution for the final product I'd recommend getting the topology correct on the lowest resolution version of your mesh that you can while maintaining the shape. Then, add in subdivisions as needed to get enough detail for your cloth.
You can also try deleting the central faces and doing a "grid fill" after applying the modifiers. This gives you a topology that might flow better for cloth simulation.

This fixes the topology, though I'll have to redo the UV maps. I'm hoping to find a solution that preserves them to retain the "cut from the same piece of fabric" look I'm trying to accomplish.
It also begs the question of maintaining the same face counts and edge lengths so they can sew properly.

You can use an object for UV projection to set up a map that won’t change as you change the topology. You can see here at around the 6:13 mark how to accomplish it. https://youtu.be/8NYNiayHvJI?si=QgXt9uYZq9WWu2OY

That doesn't preserve the existing UV map. It's just another method of baking the texture to a low-poly object, and not what I'm doing.


text:
Switching Materials On Command
Ok, so here's the setup: I'm working on a model of a spaceship, using Cycles as the renderer. Eventually, this model may end up in a game (possibly under Unity or Unreal Engine). The ship has multiple light objects (running lights, cockpit lighting, etc.)
While the exact materials for each light will depend on the lamp, all will have materials for an Off/On state. Some lights may have multiple colors to indicate status (IE, the engine lights will have Off, Red, Amber, and Green depending on the engine's condition).
Right now, I'm selecting faces and manually applying the materials when I want to render lights off vs. on. Which is fine when I'm working in Blender and only want to adjust one light at a time. However what about when I actually try to bring this into a game engine? I may not be able to swap materials in and out in this manner. And is there a way I can dynamically switch between the On/Off state when working in Blender, especially once I begin rigging and animating the switches and toggles on the control panel?

You could use a value node to control your node setting. And in game engine, it should be a separated part or at least you need more then one material to switch. How to switch material depend on how you want to use them, game engine should contain plenty of method to deal with these situation by scripting or something else.

And if in unity, you can directly change the diffuse color in code and runtime. That should be the most common case to deal with it.

There's actually several places where I would want to change materials:

Lighting: Having a "Lights Off" and "Lights On," as well as various light status codes (Red, Yellow, Green). This is particularly complicated because it's not just changing colors, but emission properties.

Engine Emissions. Again, an "Engines On" vs. "Engines Off."

Squadron Markings: In the ship I'm working on, the squadron is identified by the tail color. So one squadron may have a red tail, another may have black, etc.

Flight Markings: Similarly to the above, what flight (four-ship division of a squadron) the ship belongs to would have a different color (Red Flight, Blue Flight, White Flight, Yellow Flight) for ID bands and other markings (think the "Yellow Wing" USN/USMC marking system prior to WWII).

Bonus: I'd love to have dynamic text, IE plane #1, 2, 3, etc. I'm using Decal Machine for those markings, so that may take a little more doing. Right now I just want to get the lighting/colors figured out.

Wait... so it has nothing to do with Blender? It seems like your asking at a wrong place BTW.

I'm also looking for a way to do it in Blender so I can more easily swap my materials in and out for testing purposes (because when you have like a dozen different lights, it's kind of a pain to select each face and reset the material). I'm also hoping that setting it up through Blender would better facilitate it in other engines.

You need to do all this on one material. Applying materials to individual faces is not going to work for rapid testing.
Once you are using only one material toggling On and off is easy and changing the color is super simple.
First off you will need a mask to differentiate what parts of the mesh will get what. I'd recommend using an image (easy to paint in texture paint mode and transferable to any game engine), but you can also use vertex colors, or proxy objects inside blender.
For my example I'm using an image, and vertex colors.
The image texture node is the mask I painted. The key to the toggling is the MixRGB node(s). The Value input node is what I'm using to control the toggling. When the value is 0 the MixRGB node is outputting 100% black, which is feed into the Fac for the Mix Shader node. (0 uses the top socket, 1 is the bottom socket) Likewise when the value is changed to 1,  the MixRGB outputs the mask image which has white painted in the proper places. Thus the Emission shader gets to shine.
Its the exact same thing for the one I have labeled "Engine toggle" except here I'm using the vertex colors as the mask instead of an image.
The RGB input is how I'm changing the color of the "lights." You could also use a image and a special UV map just to re color (You would simply move the UVs to a different color) but for in blender the node is much easier.

The nodes can look much neater when wrapped in a node group, but for testing I prefer access straight to the nodes.

Maybe instead of using 0 .333 .666 and 1, have each color as an on/off value. So if Yellow is 1 and all other lights are 0, the light will be yellow. Ditto Red and Green.

Ah, I've got it. It took adding a couple extra mix shaders to cover the other light statuses, but I've got it set so that if all values are 0, the light is off, and I can then switch between the statuses by setting each value to 1.

I can see where I can use this for my squadron/flight colors, as well, including NOT showing them (IE, a flight leader in my marking scheme has a band around the fuselage, but a wingman would not).

So I've got two materials working, but I'm running into problems trying to get a third. I'm using Vertex Colors for the mask, and have a base color that's painted Black, while the other two are White and Blue. I can get the White group to work, but not the Blue.

Ok, so here's an update based on my response to @David. This is what the mesh looks like right now:

Right now, I have my new material applied in three places: The metal grate on the floor, everything that's green, and that stripe across the top of the dashboard.
My floor and the base color are working just fine. However that stripe across the top of the dash SHOULD be the same color as the rest (so...black). As you can see, that's obviously not the case.
Here's what my shader looks like right now:

The base cockpit color has been painted Black with Vertex Paint. The metal grate on the floor has been painted White. The stripe on the dash has been painted Blue. However I've tried a number of tweaks and permutations of the shader, and just can't get that stripe to the correct color (it should be using the AntiGlare group). I've tried changing the Factor to Color 1 and Color 2, I've tried using the Color node, I've tried changing the unlinked Color to Black, White, and Blue, and I've tried changing the Value
Eventually I want to get as much of this onto one material as possible, I'm just going a little at a time so I don't screw it all up at once.
Also, I'm having a little trouble figuring out how exactly to connect the Displacement node on the floor.


text:
Retopologizing Hard Surface Model - Controlling Solidify
While retopologizing a model for 3D printing, I'm running into some issues with solidifying the mesh. Since I'm going to be printing this I obviously can't leave as 2d planes. However, I'm also going to have to break the model up into parts for printing, and I don't want to have them in solid chunks because there's going to be places I'm going to be putting some interior details (landing gear wells, cockpit, maintenance spaces, open engine bays, etc).
I figured the easiest way to get uniform thickness would be with a Solidify modifier, however this has a particular problem:

The Solidify modifier tries to keep the extruded edges perpendicular to the source mesh, however there's places where this doesn't work for me. For example, the lower half of the hull needs to be able to meet flush with the upper half, so I want that joint to be flat, as noted in the red.

In other places, I want the vertical edges to be at an angle, rather than straight, as shown in red here.
Is there a way that the Solidify modifier can be controlled in this manner? Or should I just complete the entire mesh as one piece first, solidify it, and then cut it up into parts?


text:
Retopologizing Hard Surface Model - Subdivision
I want to use subdivisions so I can smooth out a model I'm retopologizing for 3D printing as much as possible, however this is giving me trouble with the places I want to keep straight. For instance, this feature here:

In the retopologized model, it looks like this once the Subdivide modifier is applied:

(Ignore the inset area, I haven't gotten to the point of retopologizing that part yet).
And this is the mesh before the Subdivision modifier is applied:

As you can see, the front "point" has been truncated slightly (not too much of an issue) and the sharp edges of the back have been rounded (this is). I don't want to use Simple because the entire point is to smooth out the surface for printing.
I've tried adding extra edge loops around it, but that hasn't helped much. I've tried putting a Solidify and Bevel modifier before the Subdivide, but that just gets me this:

So my straight edges are there...but it's still putting the curve on top of it.
I don't want to use creases if I can avoid it, because then I have problems with this:

This is supposed to be a cylinder, but where there are multiple objects (such as landing gear doors or panels I want to be able to leave "open" on my printed model) the curve doesn't match up and it ends up as more of a slight lemon shape (it happens other places there are curved sections, including those WITHOUT multiple objects, but it's most noticeable here).

I may have found a partial work around to the cutout issue. I created a mesh from the cutout, and then used a Boolean Difference Modifier after the Subdivision and Solidify in the stack. The problem is I can't use Bevel Weights to bevel the edge of the cutout. Unless someone has a better idea of how to fix those corners.


text:
Can I set the Brick Texture Node horizontal mortar size to be equivalent to the vertical mortar size?
I'm using Blender 2.73 and I'm trying to create tiles using the brick texture node.  The problem I'm having is that the horizontal mortar size is smaller than the vertical.
Is it possible to have them be equivalent sizes?

Could you better explain what you mean - maybe post some screenshots. From my testing, it seems they're already of the same size, so I'm not sure what you mean.

I think pressing Ctrl+A and applying scale while the object is selected might help.

The main reason of this answer is to combat the erroneous views as to why the brick texture is distorted.
The mortar attribute is a constant set by the Mortar Size option, not a percentage.

This issue is caused by scaling the mesh that the texture is applied to. Applying the scale will not change anything, as the generated UV's for the brick texture still remain the same. You need to UV unwrap your mesh properly and use that to drive the brick texture UV coordinates.
A default plane will give this result:

While a scaled one will give this result:

Again, applying scale does nothing. I tried it, several times. Instead, UV unwrap the mesh and set up your nodes like this (or try @chebhou's suggestion):

Now you can change the UV unwrapping and the mortar will change in width as well. You may need to change the size of your bricks once you have the mortar size correct.

the mortar size is a percentage of the width or height so they won't be equal unless width = height
or  you can try this :

tweak the scale on the Y axis till you get the effect

This is not the case. I changed the width to an outrageously large size, and kept the height, and the mortar sizes remained the same. Whats more, the mortar size is consistent.

Although this method does work at achieving the desired result I had to change the accepted answer to best solution.


text:
Export a single frame as a new Blender model
I've got a horrendously complex ship model that has two states that I wish to work with. Unfortunately I managed to produce 76 frames of animation - they looked smooth when I first did it. However I knew nothing about the origin business and I've gotten into great difficulties with Blender resetting where different objects are when I save and reopen the file.
What I wish to do is save frame 1 as a new model and frame 76 as a new model, then figure out how to reset all the geometry so all the wings and things are not everywhere.
Is there a way I can do this? I've found nothing obvious yet.
The horrendously complicated bit is the fact that it's over a million triangles - probably shouldn't be - but I didn't know how to get the detail I wanted any other way at the time.

If it's only one mesh, no matter how much poly count it has, the procedure will be quite easy.

Make a backup file of your ship.
In "on work" file, duplicate the ship.
Set timeline on 1 keyframe and delete all keyframes for original ship (this way you will get the ship in 1 frame position)
Set timeline on 76 keyframe and delete all keyframes for second ship (this way you will get second ship in 76 frame position).
You probably would want to have this ships on different layers for better performance. From this point you can proceed with whatever you want to achieve with this project.


text:
Why is my scene rendered repeatedly when I press F12?
I hit F12, tiles all render out - just as the final image appears, the whole lot disappears only for it to start all over again.
I've not specified multiple frames or any animation, so can anyone explain why this happens and what it's for?

In version 2.8 of Blender, in Properties > View Layer > View Layer, check the Render Single Layer option.


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Blender 2.8 UV Does not appear?
I'm having difficulty with this one. I've used UV unwrap on simple objects and texture painted them just fine. However I cannot get an unwrapped UV to show up in the editor on this model. I'm certain I'm missing something basic but my Google fu has ran out.
I've got everything selected, have used Project to View on this example but doesn't make a difference really. What am I missing? Any help gratefully received.
Am on Dec 26th build of Blender 2.8 but it's been like this for a while. May be nothing to do with it being 2.8 I realised.

It appears that you are doing everything right (they have recently split the UV and the Image editor, and you seem to be correctly using the former). The only thing I can suggest is doing "A" on the UV window, then ".", to rule out the entire UV map being out of the display limits

Thank you - nothing changed really. It bought up a pie menu and I tried the different options. For some mystery reason, it's not working on this model in this version. I'll try again on final release I think. I was only after making the mapped texture far more refined as it's pixelated on the transparent faces.

Oh sorry I meant to say "." from the numpad, not the one from the letter keyboard

can you share the file?

I think I gave up over the Xmas holiday. Sadly some roadblocks do knock me way off course for such a long time that I lose skills I had previously :( Which sucks badly.

You need to hit UV Sync Selection (The 2 arrows)

Thanks for that.  Worked great!

I had this problem today and I found a solution for my case:

This is exactly what happened in my case. My file was (inexplicably) not showing UV Islands anymore. Show Overlays will hide everything in the UV editor. Who knew, right?

You can trying to make a new Workspace
I had that problem with the OLD (2.79) files

To get a UV image to display on an object in the 3D viewport I had to go to the materials tab, click the little circle button to the right of 'Base Color', select Image Texture then select the image I used in the UV.

Change in the panel as shown in the image from View to Uv_Edit.
Good luck

Go to object dat properties panel, open the uv maps section and delete the current uv map. Then just create a new one. That fixed it for me .

For me, my UV map was missing, I parented an object to another one, and the parent UVmap got deleted somehow.

I'm running 3.6 and had this issue come up and it turned out to be there were 2 UV maps listed in the Data properties tab under UV Maps. I deleted both then unwrapped the object again and the object unwrapped properly.

I had that issue today.  The UV was there, just not showing up properly in the editor or texture paint space.  It was just a simple wall so I marked seam on every edge and did a smart UV project.  It showed up perfectly and I could see there were some weird linkages between a couple of vertices that were not even connected on the object.  Good enough to work with though.

just change image editor to uv editor in the corner

I had the same problem and nothing and no advice online helped, what I did was save the file I was working on , opened a new blender, append my job from previous and all worked again !


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Bounding box like object stuck in viewport
I've used Blender for 4 years, off and on, yet I've never come across this before. I've attached two images to try and make it clear. It looks like a bounding box, it's not an object I've added and I cannot find anyway to get rid of it. Wasn't there last night.
Can anyone tell me the "Kick myself" short cut to get rid of it please? As I've not the foggiest.
Thank you!

[

See Properties editor > Object tab > Display rollout if there aren't any options activated like Texture Space or Bounding Box, maybe related https://blender.stackexchange.com/questions/13417/yellow-dotted-wireframe-appears-when-i-mistakenly-press-shift-t-instead-of-ctrl and https://blender.stackexchange.com/questions/3366/display-bounding-box-around-objects

Thanks to Mr Zak's links, the answer-for anyone else stuck, unable to find a good Google phrase to find it-is in the Object->Display menu.
You get it by hitting Shift-T by accident!

Just to flesh this out.. Shit-T displays the Texture Space of the object, which can be scaled or translated .. you don't seem to be able to rotate it? I can't see why not...


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Cloth Sewing Issues
I'm working on making some clothes, specifically this shirt design:

However, I'm running into some issues with the cloth simulation
The first, is that the top side of the sleeve ends up pinched into a sharp edge and isn't "falling" onto the top of the arm:

The second is here at the collar. As you can see it's not going forward enough on the neckline, and it's bunching up in the rear:

Third, the back of the shirt is bunching up here in back, rather than hanging down naturally.
Here's the mesh, which is modeled on the actual pattern:

I've tried subdividing the mesh further, adding a Solidify modifier, I've tweaked the cloth physics, made several adjustments to the height and width of the front and back pieces, added additional loops to make the collar bigger, but am not having any luck getting things to lay right.
Is there something that I'm doing wrong?

Hello please share your file: https://blend-exchange.com/

On real garments, the sleeves are sewn together at the bottom. The collar and the cuffs of the sleeves can be created separately and then added to the pin group. Here is a related question with an example: https://blender.stackexchange.com/q/306797/107598. and here is A Tailor's Approach to Cloth Sewing in Blender on YT. It's a very detailed and very accurate "tutorial" that might be helpful. (It's more like a course/live stream (8 hours) but you can watch it at 2x speed.)

I figured out a solution. I made the collar one piece and used a Bend modifier through the Simply Cloth plugin to curve to the shape I wanted before sewing it.


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Eyes/ Double Transform
When i translate the Torso/Root controller, the eye look at works as it should but the individual eye targets inherit double transform, which result in eyes facing in another direction.
How do i fix this?

I don't quite understand. could you post a .blend?

You have a bone in between the eyes that gets left behind after you moved the rig, shouldn't it be parented to another bone to move with them?

Thanks Sambler. I overlooked the parenting of the minds eye (the parent of the two individual eyes). Minds eye was not parented to the head deformation bone which was causing the problem. Its fixed now.

As Chetan Trivedi said:

.. . I overlooked the parenting of the minds eye (the parent of the two individual eyes). Minds eye was not parented to the head deformation bone which was causing the problem. Its fixed now.

Posted to take this off of the un-answered list


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Texture Painting, problem with bump painting
Whenever i am painting bump maps, it paints on the color map. I read on one of the other thread and made sure of these five things.

Even though, I have the bump map selected in image editor, when i paint in texture paint mode, it still paints on the color map. What am i doing wrong?

Are you using BI or cycles? Note that the texture painting system changed a bit recently. Related: http://blender.stackexchange.com/q/17948/599

I am using BI at the moment.


text:
NLE - Workflow for editing one big video clip containing many sequences
I'm not sure what would be a good way to edit a big video clip containing many distinct sequences.
Before starting to put the final video together, I'd like to cut the individual sequences, give them a name, and put them in a place from where they will be easily accessible later. It would be great if my timeline could avoid being used as a 'storage' location, since I think it would clutter the view of the actual edit.
What I've done up until now :

Imported the video file, and made a meta-clip containing the audio and video clip.
Made soft cuts at every sequence break, and given all meta-clips relevant names

One way I can think of to proceed would be to export all the meta-clips as individual videos, and then make a separate blender file to make the final video by importing the intermediate files.
Is there an automated way to do this, or is there a better solution?

Try adding another scene named after the clip then import the long clip. Soft cut it or metastrip the parts as you wish. Then copy paste these elements back to the master edit scene.
You can have as many additional clip scenes as you wish.


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Constraining vertices in the Z axis when array, curve and shrinkwrap modifiers applied
I'm creating a road on a 3D landscape.  The road's path is defined in the X and Y axes using a bezier.  I've created a small section which I'm then applying to the bezier using an array modifier and then a curve modifier.
To make the road follow the landscape, I'm applying a shrinkwrap modifier to it using project mode on the Z axis.
The issue is that where the road curves around on a sloping hillside, one side of the road is lower than the other.
What is the best solution to make the road level please?

I managed to solve the problem by using the shrinkwrap modifier on the bezier so it followed the terrain, then I simply applied the road section to the bezier using the array and curve modifiers.
Set the bezier twisting setting to 'Z-Up'.
It was necessary to hit 'apply' to the shrinkwrap modifier on the bezier, otherwise the road simply followed it in 2D.
I hope that helps someone.


text:
What is a good approach to reduce the number of faces on this chair model
See the model below. I first scanned it with a 3D scanner and then remodelled every part of it. I used the subdivision modifier a lot. Resulting in a smooth surface. Sometimes a surface is completely flat, like the top of the seat for instance. I used the subdiv modifier here to get a smooth curvature on the edges.
Is it good practice to reduce the number of faces on flat surfaces? I am thinking of modelling for VR environments for instance. What is a good approach to reduce the number of faces on this seat, for instance.

Separate all the faces (object parts) you want to simplify. So you'll have another object. Set a 'decimate' modifier to it and use 'unsubdivide' option (probably with a pair amount of iterations).

@lemon First splitting the object to use the modifier is a great idea! And I should join this object later on right? Preferably also connecting the 2 meshes to form a single on, right?

If you were taking a sub-d approach, I don't see anything in this particular model which requires tricky transitions from high-density to low-density mesh, especially if you can model separate parts as separate parts, which is the general rule, unless you need a manifold surface (for example, for printing).
You would be aiming for the lowest possible number of edge-loops to capture the curvature of the piece .. let's say, the seat-base...

..shown here with a) the model as made, as a cage over the subdivided surface, b) the cage conforming to the subdivision modifier, optimal display on, and c) the underlying subdivision, level 2.
So, if you chose to go that way, you would dissolve nearly all the edge-loops, keeping only those needed to capture the curvature and sharpen edges, assign a Subdivision Surface modifier, and apply it at the last possible moment, if at all.
If you were really pushed for your poly-count, completely flat areas isolated from the surrounding curvature can be N-gons. You could apply the subdivision, and dissolve all the edges in the flat area (maybe insetting the N-gon to protect the surrounding curves), and cut in just enough edges to get rid of smoothing artifacts resulting from triangulation.

You can reduce the number of quads on a flat surface without generating Ngons with edges poles in red, by doing something like this (I don't know the name of that specific kind of retopology)
High poly is useful for boolean operations or deformation, to reduce the number of polygons, and keeping detail you can use for baking.


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How to render all cameras in the scene automatically
How can I render all cameras in the blender scene automatically, with multiple resolutions and sampling set per camera? I'm using Blender 2.8
The reason I am looking for automation is the following: when the model is remodelled, the old renders are outdated and new ones must be created. Doing so manually for multiple cameras, with each their own settings, is time consuming (and boring).

You can use a script for that. This repo on github has Render.py. It uses a settings file for each camera (or the default if no camera specific setting is found). So for each camera multiple resolutions and sampling settings can be defined. Put the render_settings.json file in the same dir as the blender file. Open the blender file and goto the scripting tab. Load and run the script.
Render.py script
import bpy
import json
import os

renderPath = bpy.path.abspath("//Renders\\")
print('Render path: ' + renderPath)
renderSettingsJsonPath = bpy.path.abspath("//render_settings.json")
print('Settings file: ' + renderSettingsJsonPath)

def ensureDirExists(file_path):
    if not os.path.exists(file_path):
        os.makedirs(file_path)

def loadRenderSettings():
    file = open(renderSettingsJsonPath,"r+")
    contents = file.read()
    file.close()
    return json.loads(contents)

ensureDirExists(renderPath)

renderSettings = loadRenderSettings()
print('Render settings loaded')

for obj in bpy.data.objects:
    if obj.type != "CAMERA":
        continue

    print('Camera with name "' + obj.name +'" found')

    renderSettingName = 'default'
    if obj.name in renderSettings:
        print('Render settings for camera found')
        renderSettingName = obj.name
    else:
        print('No settings for camera found, default settings will apply.')

    if renderSettingName not in renderSettings:
        print('No render settings for "' + renderSettingName + '" not found, skipping')
        continue;

    bpy.context.scene.camera = obj
    print('Active camera set to ' + obj.name)

    for renderSetting in renderSettings[renderSettingName]:
        resolution = renderSetting['resolution']
        resX = resolution['x']
        resY = resolution['y']
        samples = renderSetting['samples']
        engine = renderSetting['engine']

        fileName = obj.name + "_" + str(resX) + "x" + str(resY) + "_s" + str(samples) + ".png"
        print('Render file name: ' + fileName)

        bpy.context.scene.render.filepath = renderPath + "\\" + fileName
        bpy.context.scene.render.resolution_x = resX
        bpy.context.scene.render.resolution_y = resY
        bpy.context.scene.render.engine = engine

        if engine == 'CYCLES':
            bpy.context.scene.cycles.samples = samples
        elif engine == 'EEVEE':
            bpy.context.scene.eevee.taa_render_samples = samples
        print('Render engine settings set')

        print('Render start')
        bpy.ops.render.render(write_still=True)
        print('Render finished')

render_settings.json
{
    "default": [
      {
        "engine": "CYCLES",
        "samples": 32,
        "resolution": {
          "x": 320,
          "y": 240
        }
      }
    ],
    "Camera": [
      {
        "engine": "CYCLES",
        "samples": 128,
        "resolution": {
          "x": 640,
          "y": 480
        }
      },
      {
        "engine": "CYCLES",
        "samples": 512,
        "resolution": {
          "x": 1920,
          "y": 1080
        }
      }
    ],
    "Camera.001": [
      {
        "engine": "CYCLES",
        "samples": 128,
        "resolution": {
          "x": 640,
          "y": 480
        }
      },
      {
        "engine": "CYCLES",
        "samples": 512,
        "resolution": {
          "x": 1920,
          "y": 1080
        }
      }
    ]
  }


text:
Normalize light fall off
I want to 3D scan an object, take pictures, determine the camera positions (using f-spy) and then texture paint (in stencil mode) the textures onto the object. Of course, the images taken have vignetting of the camera, and of course the lighting in the area is not homogenous.
I am wondering if there is a (feasible) way to normalize the light, so the textures on the object do not have the 'baked' lighting of the original images taking. (Taken into account the vignetting was normalized already).
Maybe it is possible in such way to put a known object in a room, photograph it,  apply 3d photogrammetry and from there calculate the position of different light sources/influences?

I don't think you will achieve good results with projection painting, unless 1) the material is diffuse and 2) you change the lighting direction between shots, so you can mask areas in the shadow. Since 2) is bad for 3D reconstruction this wouldn't be a good approach. Removing lighting is a topic of research, however the estimation is difficult because it depends on the material properties, e.g. glossy materials behave different in light than diffuse ones. Professional photogrammetry software include features for lighting removal which work for simpler cases.


text:
How can I add a description to an object
Question:
How can I add a description to an object. Preferably being able to shows this on top of the object, as an overlay. And that the description can be toggled to show/hide.
Background:
This background info does not add extra explanation to the question being asked, but I wanted to share when the question arose. I'm modelling something to print with FDM. I wish to print without supports if possible. On some object I have used the boolean operation on a pipe. The problem is, the printing on the top of the hole where the pipe will fit isn't printed very well. This makes the hole just a bit too tight. So I stretched the hole for the pipe very little. This you can not see easily in the model. Hence I would like to add a description on the object, stating it is adjusted for 3D FDM printing. Preferably the text shows as an overlay on the object.

Possible duplicate of add custom texts(labels or annotations) which are always upright to user in view port

Related https://blender.stackexchange.com/questions/15729/metadata-notes-comments-in-blend-files


text:
Geometry showing through when X-ray is off
I've messed up with the rendering/clipping distance or something, because now geometry is showing through solid faces in edit mode at a relatively close distance to the object, which was not the case before:

And probably related to this issue, the intersection between two volumes is being rendered in the viewport as jagged edges:

Is there a slider somewhere that fixes this?

Turns out I needed to turn down the clipping distance in "N-panel > View > View > [Clip] End".


text:
Why do I get large bevels on a curve with such a small bevel object?
I am bevelling a simple circle with another simple circle and as you can see from the screen shot below I have to make the bevel circle incredibly small and I still end up with a very large cross section. I don't understand why the cross section on the bevelled curve isn't the same size as the bevel curve.

Is the scale applied to both curves? (Ctrl+A)

When resizing the bevel shape are you in edit mode or object mode?

Ok, Ctrl-A and selecting rotation and scale worked. I'm not sure why though. Thanks for all the comments. I'll go investigate ctrl-A now...

You will have to :

apply the scale Ctrl+A
select all point of the curve and reset the radius back to 1 :

Note : to avoid applying the scale just set the radius to  1/scale

Once you've selected a bevel object, the bevel_depth and bevel_resolution parameter doesn't affect the bevel. Rescale the bevel object in Object or Edit mode, and you will see a change in the final geometry that the Curve uses.

and


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Can one see static forces in Blender?
I have just started with Blender and normally I would dig into the manual first (so far I have done little more than do the ginger bread man tutorial). But this month I have to do an assignment for which I want to see the forces acting inside a model under a static load (a hook with a coat hanging on it) and I was wondering if I could do this with Blender.
I have briefly looked through the physics section of the manual. I don't quite understand all of it yet, but what I gathered so far is that weight is not physical weight but the number of vertices (so in a way the complexity of the model), particles aren't physical particles and physics only works for fluids. Is that correct?
And the static physics section doesn't seem to cover it either.

forget blender for this job, it has 0 tools for such visualizations.

Well.. You might be able to do something with soft bodies, but blender really isn't made to do this kind of thing.


text:
"bpy.path.abspath" not working properly
So I currently have this string: "//..\Desktop\vine.png"
However, to use it when loading an image I need the \ to be \\ , so:    "//..\\Desktop\\vine.png"
path = "//..\Desktop\vine.png"
image = bpy.data.images.load(path)

I've tried using
bpy.path.abspath(path)

however this is what it throws back at me:

For some reason it changes the "v" to "x0b" and doesn't change the last \ to a \\
Anyone have any ideas why this might be? Or any other methods to change the \ to \\

I did some more tests, it seems like it doesn't work if the image starts with following letters: v, n, b, x, f, a, u

use path = "//..\Desktop\\vine.png" or path = r"//..\Desktop\vine.png"

the path is generated, do you know if there is a way to use the r if path is a variable? like: bpy.path.abspath(r + path) ?

s = s.replace("\", "\\")   -- http://stackoverflow.com/questions/7262828/python-how-to-convert-string-literal-to-raw-string-literal


text:
Why are the normals of this primitive circle pointing upwards, and how to reset them?
Using Blender 2.8, when creating a primitive circle using the API like this:
import bpy
from mathutils import Vector, Euler
bpy.ops.mesh.primitive_circle_add(vertices=8, enter_editmode=False, location=(0, 0, 0.03), rotation=Euler((0,0,0.3927)), radius=0.05)
bpy.ops.object.transform_apply()

It ends up with normals like this, pointing upwards a bit:

I noticed when not setting the location of the circle, like so, it does not happen.
import bpy
from mathutils import Vector, Euler
bpy.ops.mesh.primitive_circle_add(vertices=8, enter_editmode=False, location=(0, 0, 0), rotation=Euler((0,0,0.3927)), radius=0.05)
bpy.ops.object.transform_apply()

I have failed thus far to understand why. In any case, I would like the normals to be pointing outwards, like so:

Is this possible? If yes, how? Thanks.

Vertices without face align their normals to the object's origin. See: https://blender.stackexchange.com/questions/10700/can-a-single-vertex-be-rotated To fix them you could set the operator's fill_type parameter to either TRIFAN or NGON and then calculate each vertex normal manually.

At first sight this behaviour seems odd, to me..I wonder why a cross-product of the edges wouldn't make more sense....

A cross-product of the edges would be more intuitive indeed, at first sight. Don't know either if it has a particular reason to let them radiate from the origin.

@RobinBetts If the edges are inline then the cross product is (0, 0, 0).

The practical part of the issue was solved by not setting the location upon creating the prmitive circle, but afterwards with a new line of code.

@batFINGER There you go! That's why 'First Sights'  need to be  composted for a while.  (At least, mine do.) Thanks!

It seems, in the absence of any faces from whose Face-Normals the Vertex-Normals can be derived, they resort to a spherical projection from the Object Origin.

Oops, hadn't noticed the dupe.


text:
3D tool add-on window locks/freezes when importing an image with Python
Code:
    import bpy
from bpy.props import *

class primitive_object_add(bpy.types.Operator):
    '''Add a minecraft item'''
    bl_idname = "mesh.primitive_object_add"
    bl_label = "Add a Minecraft item"
    bl_options = {'REGISTER', 'UNDO'}
    img_str = StringProperty(name="Path:", default="", subtype='FILE_PATH')
    opt = IntProperty(name="Option 2:")

    def execute(self, context):
        if self.img_str != "":
            path = r"" + bpy.path.abspath(self.img_str)
            image = bpy.data.images.load(path)
        return {'FINISHED'}

def menu_func(self, context):
    self.layout.operator("mesh.primitive_object_add", text="Object", icon='OBJECT_DATA')
def register():
   bpy.utils.register_module(__name__)
   bpy.types.INFO_MT_mesh_add.append(menu_func)
def unregister():
    bpy.utils.unregister_module(__name__)
    bpy.types.INFO_MT_mesh_add.remove(menu_func)
if __name__ == "__main__":
    register()

So if running this code, following happens:
You get up the menu and everything just fine

Then clicking the file browser icon, which will bring up the file browser, so far everything is working.

However, now when selecting an image and pressing accept, will load the image into blender properly, but it locks/freezes the toolbar, so now I cannot change Option 2 if I would like to.

I've spent pretty much the entire day yesterday trying to fix this, but without any luck. I discovered that for some reason if you where to press "Object" in the add menu 2 times and then using the file browser to load in an image it works, and it will work until you close and open blender again.
Does anyone have any idea on why this might be happening, and a way to fix it or go around the problem?

see this alternative http://blender.stackexchange.com/a/17829/5113

@Chebhou The problem using 'bpy.ops.image.open("INVOKE_DEFAULT")' is that for the add-on I'm working on I need a reference to the image, and the action needs to happen when pressing a button, and if I'm not mistaken it's not possible to add buttons in the current panel I'm using.

you can add buttons,  and if you need a ref to the image store a list of the images before calling the Op then compare it with the new list the new entry is yours

@Chebho Sounds like that could work, however with my limited knowledge of Python I have no idea on how I would do this. Any chance you could help me out? (It would of course be paid). If you're interested, hit me up at contact@rymdnisse.net

there's a problem that the image is not pushed into the bpy.data until the operator is finished which make it impossible to find a reference for so you may have to create a panel for your addon to avoid all this hustle  if you can add more details I may be able to help


text:
Blender 2.71 Preview Showing Incorrectly
I am tinkering with UV mapping a skybox onto a cube (sideways T shape image)
So with the UV map settings and the actual render working correctly, I've been noticing the preview box in cube. It looks like this:

How do I fix it to show the texture wrapping around?

The preview is unlikely to match the finished render because you are using UV mapping. To have the preview cube match the finished render would require the preview cube to be using the same uv mapping that you are using. The preview isn't able to do this because it isn't aware what object the material is being applied to and has no connection to your object.
The material preview is used to answer the question "What would my material look like if it were applied to different objects?" but not "What will the material look like on my specific object?" The fact that your object, a cube, looks like the preview, also a cube, is just coincidence.
Setting the viewport to 'Rendered' shading mode is the best way to preview how the material will look on your object.

I like the suggestion/information  regarding the best way to preview in [Rendered Shading Mode].  It went beyond the original question and is still related.  In this forum we probably cannot directly change or "fix" this preview aspect of blender as the question was posed.  The suggestion/information allows the user to think differently and productively about the problem with related techniques.

You render works correctly. You are successful and golden.  The preview is to get some quick, low cost, color and transparency sense of a material.  If you model the Eiffel Tower it will not show up in the Material Texture preview as a Small Eiffel Tower.  If I model a sphere I can select the Monkey preview.
Lastly as your question was posed probably no one except software developers can change or "fix" the preview.  It may be difficult to even find some precise written specification for the preview.  So I am certainly not in the position to [say] that any change would "fix" anything to any large consensus because I did not create the specification.  The value of the preview had been validated by years of experienced users.

I would expect off-results if you used a monkey preview on a spherical mesh. But I'm explicitly doing a simple textured cube which I would expect the preview to show it kind of right, rather than simply showing the entire skybox image once per side.
Obviously, as you said, I'm golden, since everything renders fine. But sometimes if something in the interface looks a bit off, in blender that tends to bite me.

@user6325 I understand your point of view.  I consider blender to be quite useful.  For the first number of months of learning [some] blender I felt like blender and its documentation were pure ev...  I have deep bite marks too.  Mostly on face and neck.


text:
Animated material transparency isn't shown in the 3d viewport
I'd love to be able to preview the alpha value of a material in the 3d viewport, but I can't figure out how to do it.
I add a material and animate it:

Assign a material to the default cube
Enable transparency for the material
Insert a keyframe for Alpha value (Z Transparency)
Move the timeline to 20
Set the alpha value to 0
Insert another keyframe for the Alpha value

I have enabled GLSL shading in the viewport properties and Texture viewport shading in the panel. When I scrub to frame 10 the Alpha value of the material is 0.5, yet it is still fully opaque in the viewport. I can render the frame and see that the material is semi-transparent. Oddly, if I toggle some Material options (e.g. Traceable), the material is displayed as expected in the viewport, but when I scrub the timeline (or alt-a to play) it isn't updated.
I'm not sure if this is a bug, or if I'm just leaving out some setting to trigger the update of the viewport display. I've tested with 2.71 and 2.72 using both an Intel and an Nvidia GPU.

Was trying with the wrong blender version, my bad.


text:
How to disable see-through mesh
I have a mesh wich currently looks like this on edit mode:

Even though I haven't activated the Z key to enter wireframe mode, I can see the edges behind the mesh. This is really annoying since I keep accidentally selecting the vertices at the back.
How can I disable this?

You need to check the "Limit Selection To Visible" button

in the toolbar in Edit mode. This will hide the back edges from view.


text:
How to stop blender from rendering world
I have an animation where some cubes are floating around on a pitch black world:

Since these are jpegs, you can't see that I chose blender to render the world transparent. But when I render, Blender will waste time rendering the transparent tiles. Even though it's only for a split second, it adds up to alot of time since it's an animation:

How can I stop this?

Short answer: you can't.
Cycles can't skip parts of a render based on what is/isn't there because it doesn't know what will be there until it has already rendered it.  So it can't skip tracing rays that only hit the world background since it doesn't know what a ray will hit without actually tracing it.

Render border
You'll have to set up a render border for your frames.

The rendering aglorithm need to make those passages because it must check the pixel to determine whether or not they should be transparent in the final images. You know they are, but the software doesn't, so it must figure it out on his own in some way.
Consider that your knowledge of that comes from a sophisticated algorithm running on your brain, which is different than Blender's one, whose approach is more brute-force oriented.
Said that, the only way it comes in my mind would be to help the software by make the area to check less extended by sharing a bit of your the information of the scene you got (e.g. excluding areas who are surely transparent).
If that is easy for a still shot, more tricky can be for an animation, where the objects move continuously across the screen. That's where Animated Render Border can be useful.
It's an add-on you can purchase in Blender Market. The author says:

This add-on makes the ‘render border’ adaptive so that the border updates its location and size every frame to always surround the selected object or group of objects*, focusing your render power on just those specific parts of the image.

And, talking about the functioning, he also says:

The add-on looks at the bounding box of the object(s) selected to be tracked and will adjust the render border accordingly.

Hello, @RayMairlot. I've proposed your addon as a possible solution to this question, if you think your work hasn't been portrayed in the appropriate way, feel free to edit.


text:
How to reset view node shortcut
I'm simply trying to use the "view node" on the node editor. I watched a video where I learned the shortcut is ctrl - shift, but it will not work.
Here I'm trying to view a wave texture:

Am I doing this right? or do I need to reset the shortcut?
Thanks for any answers!

This behaviour is a part of Node Wrangler addon, see http://blender.stackexchange.com/questions/1691/way-of-seeing-data-as-image-anywhere-in-a-cycles-nodes-setup. No need to reset any shortcut, just make sure addon is enabled and you click on the node itself. The result can be seen while in Rendered shading mode if reviewing material nodes.

While DaurteFarrajotaRamos's answer is correct that there is no viewer node by default, Greg Zaal's Node Wrangler addon (which comes bundled with Blender) does implement a veiwer node of sorts in the node editor.
With Node Wrangler on, when you Shift+click a node it will connect it to the Material Output node, making it visible on the object and in the preview rollout pane.  It will connect surface shaders directly to the Surface output, volume shaders directly to the Volume output, and all other datatypes (colors, vectors, and values) will be sent through an emission shader plugged inot the Surface output.

View node is available for compositing node trees only, not material or texture ones. You seem to be using Blender Cycles nodes in your image, so for those there is no preview node available.
If you want to preview the created material either use the interactive preview in the 3D window by drawing a border around your object with Ctrl + B and then pressing Shift + Z or use the preview panel in the Properties Window > Material Tab > Preview


text:
where can I download a "text" addon?
I'm not very good in the subject of addons, and when I wanted to be able to add a polysphere on blender, I googled around and found an "Add_mesh_round_cube" addon which I believe should be correct. It's on the blender developer website, so I think it's quite a legitimate source:

When I selected the addon on the list (as seen above) I came to this page:

Apparently this is the python text of the addon. But I don't know how to proceed from here. Can anyone help me out?
Thanks for reading!

just as a side note, what's wrong with using shift+a, add uv sphere in the 3d viewport?

Possible duplicate of Installing an addon

Alias guru, I want to add polyspheres intead because UV-spheres will pinch detail at the poles, whereas the polysphere has only quads and the detail is all nicely distributed, and it makes for some great topology

It is included into Extra Objects addon; if you want it separate find it on github. In general, if you see an addon in plane text, select it and save to a file with .py extension.

Select the text and copy it, then paste it into a text editor and save it as something like Add_mesh_round_cube.py (make sure to give it the .py extension).  Now you can load it into Blender like any other addon.  Open the User Preferences (Ctrl+Alt+U) and go to the Addons tab, then hit Install From File and select the file from your computer.  Then click the little checkmark next to it to enable it.
Note that, as others have mentioned, the specific addon you are looking at is already bundled in Blender by default, so you can just find it in the list and enable it.