canvas-alpha-bug.html

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Copyright (c) 2019 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>Alpha blending bug on WebGL canvas</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>

</head>

<body>

<div id="description"></div>

<div id="console"></div>

<canvas id="canvas" width="128" height="128"> </canvas>

<script id="vshader" type="x-shader/x-vertex">

attribute vec2 a_position;

varying vec2 v_uv;

void main()

    v_uv = a_position.xy * vec2(0.5, 0.5) + vec2(0.5, 0.5);

    gl_Position = vec4(a_position.xy, 0.0, 1.0);

</script>

<script id="fshader" type="x-shader/x-fragment">

precision mediump float;

varying vec2 v_uv;

uniform sampler2D u_texture;

uniform vec4 u_color;

void main()

    vec4 tex = texture2D(u_texture, v_uv);

    gl_FragColor = tex * u_color;

</script>

<script>

"use strict";

// This test exposes an Intel driver issue on macOS.

var wtu = WebGLTestUtils;

var gl = wtu.create3DContext("canvas");

var program;

var offscreen_tex;

var fbo;

function init()

    // Init program

    program = wtu.setupProgram(gl, ["vshader", "fshader"], ["a_position"]);

    // Init offscreen render targets and specify the format of offscreen texture to be RGB.

    offscreen_tex = gl.createTexture();

    gl.activeTexture(gl.TEXTURE0);

    gl.bindTexture(gl.TEXTURE_2D, offscreen_tex);

    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);

    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);

    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB, canvas.width, canvas.height, 0, gl.RGB, gl.UNSIGNED_BYTE, null);

    fbo = gl.createFramebuffer();

    gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);

    gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, offscreen_tex, 0);

    // Init blend state

    gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);

function draw_rect()

    gl.useProgram(program);

    gl.bindTexture(gl.TEXTURE_2D, offscreen_tex);

    var u_tex_loc = gl.getUniformLocation(program, 'u_texture');

    gl.uniform1i(u_tex_loc, 0);

    wtu.setupUnitQuad(gl);

    wtu.drawFloatColorQuad(gl, [1.0, 1.0, 1.0, 1.0]);

function test_canvas_alpha() {

    init();

    // Clear offscreen texture to Green

    gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);

    gl.viewport(0, 0, canvas.width, canvas.height);

    gl.clearColor(0.0, 1.0, 0.0, 1.0);

    gl.clear(gl.COLOR_BUFFER_BIT);

    // Clear default framebuffer

    gl.bindFramebuffer(gl.FRAMEBUFFER, null);

    gl.viewport(0, 0, canvas.width, canvas.height);

    gl.clearColor(1.0, 0.0, 0.0, 1.0);

    gl.clear(gl.COLOR_BUFFER_BIT);

    // Enable alpha blending and render to default framebuffer

    gl.enable(gl.BLEND);

    draw_rect();

    wtu.checkCanvasRect(gl, 0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight, [0, 255, 0, 255]);

test_canvas_alpha();

description("Exposes alpha blending bug in Intel drivers on macOS - see https://crbug.com/886970");

var successfullyParsed = true;

</script>

<script src="../../js/js-test-post.js"></script>

</body>

</html>