[html][canvas] Get clear lines
[html][canvas] Get clear lines

You need a calculation to get a crisp line, because canvas grid is a
pixel. If you draw 1 width line, you need to draw a line after 0.5 pixel.

https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API/Tutorial/Applying_styles_and_colors#a_linewidth_example

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