<!--
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.
-->

<!DOCTYPE html>
<html>
<head>
<title>Micro-benchmark for WebGL drawElements index validation</title>
<style>
canvas {
    border: 1px solid #000;
}
</style>
<script src="../js/webgl-test-utils.js"></script>
<script type="application/javascript">
"use strict";

var wtu = WebGLTestUtils;

var totalTimeTest1 = 0;
var totalTimeTest2 = 0;
var totalTimeTest3 = 0;
var iterationsLeft = 10; // How many times to run the full test.
var indexCount = 500001; // Divisible by 3.

var indices = [];
for (var i = 0; i < indexCount - 1; ++i) {
    indices.push(0);
    indices.push(1);
    indices.push(2);
    indices.push(3);
}
indices.push(4);

var fullIndicesArray = new Uint16Array(indices);

var drawIterations = 50;

var errorsCorrect = true;

var log = function(msg) {
    console.log(msg);
    var p = document.createElement('p');
    p.textContent = msg;
    document.body.appendChild(p);
};

var runTestIteration = function() {
    var canvas = document.createElement('canvas');
    canvas.width = 10;
    canvas.height = 10;
    var gl = wtu.create3DContext(canvas);
    document.body.appendChild(canvas);

    var location = 0;
    wtu.setupSimpleColorProgram(gl, location);

    var verts = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, verts);
    var vertData = new Float32Array([-1, -1,
                                     -1, 1,
                                     1, -1,
                                     1, 1]);
    gl.bufferData(gl.ARRAY_BUFFER, vertData, gl.STATIC_DRAW);
    gl.vertexAttribPointer(location, 2, gl.FLOAT, false, 0, 0);
    gl.enableVertexAttribArray(location);

    var indexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, fullIndicesArray, gl.DYNAMIC_DRAW);
    gl.finish();

    var measureTime = function(f) {
        var startTime = new Date().getTime();
        f();
        var error = gl.getError();
        var endTime = new Date().getTime();
        errorsCorrect = errorsCorrect && error == gl.INVALID_OPERATION;
        return endTime - startTime;
    };

    // The buffer has at least one out-of-range index from the start,
    // so only validation will happen, not drawing.

    totalTimeTest1 += measureTime(function() {
        for (var i = 0; i < drawIterations; ++i) {
            // Change all data, which will cause complete revalidation of the index buffer.
            gl.bufferSubData(gl.ELEMENT_ARRAY_BUFFER, 0, fullIndicesArray);
            gl.drawElements(gl.TRIANGLES, indices.length, gl.UNSIGNED_SHORT, 0);
        }
    });

    totalTimeTest2 += measureTime(function() {
        for (var i = 0; i < drawIterations; ++i) {
            // Change only one index and vary the amount of referenced indices.
            // These should not be a big problem to a smart implementation.
            gl.bufferSubData(gl.ELEMENT_ARRAY_BUFFER, Math.floor(indices.length / 2), new Uint16Array([i + 5]));
            gl.drawElements(gl.TRIANGLES, indices.length - i * 3, gl.UNSIGNED_SHORT, 0);
        }
    });

    totalTimeTest3 += measureTime(function() {
        for (var i = 0; i < drawIterations; ++i) {
            // Change data at two indices to cause completely revalidating the index buffer in
            // current implementations in Chrome and Firefox (as of March 17th 2014).
            gl.bufferSubData(gl.ELEMENT_ARRAY_BUFFER, 0, new Uint16Array([i + 5]));
            gl.bufferSubData(gl.ELEMENT_ARRAY_BUFFER, indices.length - 1, new Uint16Array([i + 5]));
            gl.drawElements(gl.TRIANGLES, indices.length, gl.UNSIGNED_SHORT, 0);
        }
    });

    setTimeout(function() {
        var lose = gl.getExtension('WEBGL_lose_context');
        lose.loseContext();
    }, 40);
};

var runTest = function() {
    if (iterationsLeft > 0) {
        runTestIteration();
        --iterationsLeft;
        setTimeout(runTest, 500);
    } else {
        log("Validation returned correct results: " + errorsCorrect);
        log('1. Time spent on full buffer updates: ' + totalTimeTest1 + ' ms');
        log('Indices uploaded and referenced by draw calls processed: ' + Math.round(indices.length * drawIterations / totalTimeTest1) + ' / ms');
        log('2. Time spent on validating single index updates while range referenced also changes on every draw call: ' + totalTimeTest2 + ' ms');
        log('Indices referenced by draw calls handled: ' + Math.round(indices.length * drawIterations / totalTimeTest2) + ' / ms');
        log('3. Time spent on validating single index updates at each end of the buffer (worst case for Firefox implementation as of March 2014, not reflective of real world performance): ' + totalTimeTest3 + ' ms');
        log('Indices referenced by draw calls handled: ' + Math.round(indices.length * drawIterations / totalTimeTest3) + ' / ms');
    }
};
</script>
</head>
<body onload="setTimeout(runTest, 100)">
<h1>Micro-benchmark for WebGL drawElements index validation</h1>
<p>Note that these test cases are completely artificial, and their results only very rough indicators of the performance of a specific part of the system.</p>
<p>The benchmark does not perform any drawing, but rather measures the time the browser takes to upload indices and to check if there are out-of-range indices.</p>
</body>
</html>
