<!--
Copyright (c) 2020 The Khronos Group Inc.
Use of this source code is governed by an MIT-style license that can be
found in the LICENSE.txt file.
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>RASTERIZER_DISCARD doesn't affect implicit clears</title>
<link rel="stylesheet" href="../../resources/js-test-style.css"/>
<script src="../../js/js-test-pre.js"></script>
<script src="../../js/webgl-test-utils.js"></script>
<script id="vshader" type="x-shader/x-vertex">#version 300 es
layout(location=0) in vec2 vPosition;
uniform float xTranslation;
void main(void) {
  gl_Position = vec4(vPosition[0] + xTranslation, vPosition[1], 0.0, 1.0);
}
</script>
<script id="fshader" type="x-shader/x-fragment">#version 300 es
precision mediump float;
uniform vec4 color;
out vec4 outColor;
void main() {
  outColor = color;
}
</script>
</head>
<body>
<canvas id="example"></canvas>
<div id="description"></div>
<div id="console"></div>
<script>
"use strict";
debug("");

description("Enabling RASTERIZER_DISCARD should not affect implicit clears");

const wtu = WebGLTestUtils;
const canvas = document.getElementById("example");
const sz = canvas.width = canvas.height = 256;
const gl = wtu.create3DContext(canvas, undefined, 2);
const NUM_FRAMES = 15;
let framesToGo = NUM_FRAMES;
let xTranslationLoc;
let colorLoc;
const positionLocation = 0;
const red = [ 1.0, 0.0, 0.0, 1.0 ];
const green = [ 0.0, 1.0, 0.0, 1.0 ];
const transparentBlackRender = [ 0, 0, 0, 0 ];
const greenRender = [ 0, 255, 0, 255 ];

if (!gl) {
    testFailed("WebGL context creation failed");
    finishTest();
} else {
    testPassed("WebGL context creation succeeded");
    runDrawTest();
}

function runDrawTest() {
    debug("Verify that draws with rasterizer discard enabled do not interfere with implicit clears");
    let prog = wtu.loadProgramFromScript(gl, "vshader", "fshader");
    gl.useProgram(prog);
    xTranslationLoc = gl.getUniformLocation(prog, "xTranslation");
    colorLoc = gl.getUniformLocation(prog, "color");
    let leftRectBuffer = gl.createBuffer();
    gl.enableVertexAttribArray(positionLocation);
    gl.bindBuffer(gl.ARRAY_BUFFER, leftRectBuffer);
    // Create a rectangle covering the left half of the viewport, in
    // normalized device coordinates.
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
         0.0,  1.0,
        -1.0,  1.0,
        -1.0, -1.0,
         0.0,  1.0,
        -1.0, -1.0,
         0.0, -1.0]), gl.STATIC_DRAW);
    gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);
    requestAnimationFrame(renderDrawTestFrame);
}

function renderDrawTestFrame() {
    // Animation is required in order to expose this bug. When it
    // occurs, the rectangle leaves trails behind it.
    gl.uniform1f(xTranslationLoc, 0.0);
    gl.enable(gl.RASTERIZER_DISCARD);
    gl.uniform4fv(colorLoc, red);
    gl.drawArrays(gl.TRIANGLES, 0, 6);
    gl.disable(gl.RASTERIZER_DISCARD);

    // Animate the rectangle from the left to the right half of the viewport.
    gl.uniform1f(xTranslationLoc, (NUM_FRAMES - framesToGo) / NUM_FRAMES);
    // Draw the last frame with green so any (incorrect) trails are visibly red.
    if (framesToGo == 0)
        gl.uniform4fv(colorLoc, green);
    gl.drawArrays(gl.TRIANGLES, 0, 6);

    if (framesToGo-- == 0) {
        // The left half of the canvas should be transparent black,
        // which comes from the implicit clear just before drawing the
        // rectangle without rasterizer discard enabled.
        wtu.checkCanvasRect(gl, 0, 0, sz / 2, sz, transparentBlackRender, "left half of canvas should be clear", 3);
        // The right half of the canvas should be solid green, from
        // the last render of the translated rectangle.
        wtu.checkCanvasRect(gl, sz / 2, 0, sz / 2, sz, greenRender, "right half of canvas should be green", 3);
        runReadPixelsTest();
    } else {
        requestAnimationFrame(renderDrawTestFrame);
    }
}

function runReadPixelsTest() {
    debug("Verify that readPixels with rasterizer discard enabled receives implicitly cleared data");
    framesToGo = NUM_FRAMES;  // Reset state.
    // Clear to transparent black.
    gl.clearColor(0.0, 0.0, 0.0, 0.0);
    gl.clear(gl.COLOR_BUFFER_BIT);
    // Start with rasterizer discard enabled.
    gl.enable(gl.RASTERIZER_DISCARD);
    requestAnimationFrame(renderReadPixelsTestFrame);
}

function renderReadPixelsTestFrame() {
    // Rasterizer discard is enabled at the beginning of this test.

    // The canvas should always contain transparent black at the beginning of the frame.
    wtu.checkCanvasRect(gl, 0, 0, sz, sz, transparentBlackRender, undefined, 3);

    gl.disable(gl.RASTERIZER_DISCARD);
    // Clear to red.
    gl.clearColor(1.0, 0.0, 0.0, 1.0);
    gl.clear(gl.COLOR_BUFFER_BIT);
    // Enable rasterizer discard again.
    gl.enable(gl.RASTERIZER_DISCARD);

    if (--framesToGo == 0) {
        finishTest();
    } else {
        requestAnimationFrame(renderReadPixelsTestFrame);
    }
}

</script>

</body>
</html>
