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webgl-color-alpha-test.html
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webgl-color-alpha-test.html
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<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<script type="text/javascript" src="webgl-utils.js"></script>
<script type="text/javascript">
/* Color-Alpha Test
*
* Clear the four quadrants of the canvas as follows:
* +------+------+
* | red |green |
* | | |
* +------+------+
* | blue |white |
* | | |
* +------+------+
* However, unlike the Color test, clear with a given alpha value.
* What effect this has depends on the context-creation args passed
* to this page.
*
* Here we check that we handle various combinations of alpha and
* premultipliedAlpha correctly.
*/
"use strict";
function renderGL(gl, value, alpha) {
gl.enable(gl.SCISSOR_TEST);
gl.scissor(0, 128, 128, 128);
gl.clearColor(value, 0.0, 0.0, alpha);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.scissor(128, 128, 128, 128);
gl.clearColor(0.0, value, 0.0, alpha);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.scissor(0, 0, 128, 128);
gl.clearColor(0.0, 0.0, value, alpha);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.scissor(128, 0, 128, 128);
gl.clearColor(value, value, value, alpha);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.finish();
}
function renderBackup(canvas, value, alpha) {
if (!arg("alpha"))
alpha = 1.0;
if (arg("alpha") && arg("premult")) {
if (alpha == 0.0)
value = 1.0;
else
value /= alpha;
}
var intValue = (value * 255) | 0;
var context = canvas.getContext("2d");
context.fillStyle = "rgba(" + intValue + ", 0, 0, " + alpha + ")";
context.fillRect(0, 0, 128, 128);
context.fillStyle = "rgba(0, " + intValue + ", 0, " + alpha + ")";
context.fillRect(128, 0, 128, 128);
context.fillStyle = "rgba(0, 0, " + intValue + ", " + alpha + ")";
context.fillRect(0, 128, 128, 128);
context.fillStyle = "rgba(" + intValue + ", " + intValue + ", " + intValue + ", " + alpha + ")";
context.fillRect(128, 128, 128, 128);
}
function onLoad() {
var canvas = document.getElementById("canvas");
var gl = initGL(canvas);
var value = arg("colorVal");
var alpha = arg("alphaVal");
if (gl)
renderGL(gl, value, alpha);
else
renderBackup(canvas, value, alpha);
}
</script>
</head>
<body onload="onLoad();">
<canvas id="canvas" width="256" height="256"></canvas>
</body>
</html>