ch10/FramebufferObject

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;
        attribute vec2 a_TexCoord;
        uniform mat4 u_MvpMatrix;
        varying vec2 v_TexCoord;

        void main()
        {
            gl_Position = u_MvpMatrix * a_Position;
            v_TexCoord = a_TexCoord;
        }
    </script>

    <script type="x-shader/x-fragment" id="FragmentShader">
        precision mediump float;

        uniform sampler2D u_Sampler;
        varying vec2 v_TexCoord;

        void main()
        {
            gl_FragColor = texture2D(u_Sampler, v_TexCoord);
        }
    </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

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

// Size of off screen
var OFFSCREEN_WIDTH = 256;
var OFFSCREEN_HEIGHT = 256;

// Coordinate transformation matrix
var g_modelMatrix = new Matrix4();
var g_mvpMatrix = new Matrix4();

// The increments of rotation angle (degrees)
var ANGLE_STEP = 30;

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

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

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

    // 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;
    }

    // Get the storage location of attribute variables and uniform variables
    var program = gl.program; // Get program object
    program.a_Position = gl.getAttribLocation(program, 'a_Position');
    program.a_TexCoord = gl.getAttribLocation(program, 'a_TexCoord');
    program.u_MvpMatrix = gl.getUniformLocation(program, 'u_MvpMatrix');
    if (program.a_Position < 0 || program.a_TexCoord < 0 || !program.u_MvpMatrix)
    {
        console.log('Failed to get the...