ch10/RotatingTriangle_contextLost

This is an example from the book "WebGL Programming Guide" by Kouichi Matsuda and Rodger Lea

by Ivan Enzhaev

HTML

<canvas id="webgl" width="400" height="400">
        Please use a browser that supports "canvas"
    </canvas>

    <script type="x-shader/x-vertex" id="VertexShader">
        attribute vec4 a_Position;
        uniform mat4 u_ModelMatrix;

        void main()
        {
            gl_Position = u_ModelMatrix * a_Position;
        }
    </script>

    <script type="x-shader/x-fragment" id="FragmentShader">
        void main()
        {
            gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
        }
    </script>

    <script src="https://dl.dropboxusercontent.com/s/ylw7v7a44xtrwv0/webgl-utils.js"></script>
    <script src="https://dl.dropboxusercontent.com/s/iz1n21c8xafd76n/webgl-debug.js"></script>
    <script src="https://dl.dropboxusercontent.com/s/subm1yzylxuao8v/cuon-utils.js"></script>
    <script src="https://dl.dropboxusercontent.com/s/jw3p82lq1cjwekg/cuon-matrix.js"></script>

JavaScript

// RotatingTriangle_contextLost.js (c) 2012 matsuda
// This is an example from the book "WebGL Programming Guide"
// by Kouichi Matsuda and Rodger Lea

// Current rotation angle
var ANGLE_STEP = 45.0;

// Current rotation angle
var g_currentAngle = 0.0; // Changed from local variable to global variable
var g_requestID; // The return value of requestAnimationFrame()

// Last time that this function was called
var g_last = Date.now();

main();
//window.onload = main;

function main()
{
    // Retrieve <canvas> element
    var canvas = document.getElementById('webgl');

    // Register event handler for context lost and context restored events
    canvas.addEventListener('webglcontextlost', contextLost, false);
    canvas.addEventListener('webglcontextrestored', function (ev) { start(canvas); }, false);

    start(canvas);   // Perform WebGL related processes
}

function start(canvas)
{
    // Get the rendering context for WebGL
    var gl = getWebGLContext(canvas);
    if (!gl)
    {
        console.log('Failed to get the rendering context for WebGL');
        return;
    }

    // Get shader elements
    var vShaderElement = document.getElementById("VertexShader");
    var fShaderElement = document.getElementById("FragmentShader");
    if (vShaderElement == null)
    {
        console.log("Failed to get the vertex shader element");
        return;
    }
    if (fShaderElement == null)
    {
        console.log("Failed to get the fragment shader element");
        return;
    }

    // Get shader sources
    var vShaderSource = vShaderElement.firstChild.textContent;
    var fShaderSource = fShaderElement.firstChild.textContent;

    // Initialize shaders
    if (!initShaders(gl, vShaderSource, fShaderSource))
    {
        console.log('Failed to intialize shaders.');
        return;
    }

    // Write the positions of vertices to a vertex shader
    var n = initVertexBuffers(gl);
    if (n < 0)
    {
        console.log('Failed to set the positions of the...