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This bug would occur after the app would render several times with the
same vertex attributes and buffers, but using a different start offset.
One of the buffers would likely have to be DYNAMIC.

See http://anglebug.com/1327 and http://crbug.com/594509

-->

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Draw with changing start vertex test</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>
<canvas id="canvas" width="16" height="16"> </canvas>
<div id="description"></div>
<div id="console"></div>
<script id="vshader" type="x-shader/x-vertex">
attribute mediump vec4 position;
attribute mediump vec4 test;
attribute mediump vec4 expected;
varying mediump vec4 color;
void main(void)
{
    gl_Position = position;
    vec4 threshold = max(abs(expected) * 0.01, 1.0 / 64.0);
    color = vec4(lessThanEqual(abs(test - expected), threshold));
}
</script>

<script id="fshader" type="x-shader/x-fragment">
varying mediump vec4 color;
void main(void)
{
    gl_FragColor = color;
}
</script>

<script>
"use strict";
description("Test calling drawArrays with repeatedly with a different start vertex");

var wtu = WebGLTestUtils;
var canvas = document.getElementById("canvas1");
var gl = wtu.create3DContext(canvas);

var program = wtu.setupProgram(gl, ["vshader", "fshader"], ["position", "test", "expected"]);

var vertexCount = 24;
var testData = new Float32Array(vertexCount);

for (var index = 0; index < vertexCount; ++index) {
    testData[index] = index;
}

var quadData = new Float32Array(14)
quadData[0] = -1.0; quadData[1] = 1.0;
quadData[2] = -1.0; quadData[3] = -1.0;
quadData[4] = 1.0;  quadData[5] = -1.0;
quadData[6] = -1.0; quadData[7] = 1.0;
quadData[8] = 1.0;  quadData[9] = -1.0;
quadData[10] = 1.0; quadData[11] = 1.0;
quadData[12] = 0.0; quadData[13] = 0.0;

var quadBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, quadBuffer);
gl.bufferData(gl.ARRAY_BUFFER, quadData, gl.STATIC_DRAW);
gl.vertexAttribPointer(0, 2, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(0);

// Must be STATIC to trigger the bug.
var testBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, testBuffer);
gl.bufferData(gl.ARRAY_BUFFER, testData, gl.STATIC_DRAW);
gl.vertexAttribPointer(1, 1, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(1);

// Must be DYNAMIC to trigger the bug.
var expectedBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, expectedBuffer);
gl.bufferData(gl.ARRAY_BUFFER, testData, gl.DYNAMIC_DRAW);
gl.vertexAttribPointer(2, 1, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(2);

function check() {
    wtu.checkCanvas(gl, [255, 255, 255, 255], "should be white");
}

gl.drawArrays(gl.TRIANGLES, 0, 6);
check()

gl.drawArrays(gl.TRIANGLES, 0, 6);
check()

gl.drawArrays(gl.TRIANGLES, 1, 6);
check()

debug("");
var successfullyParsed = true;
</script>

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