ch05/MultiAttributeColor

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 vec4 a_Color;
        varying vec4 v_Color; // varying variable

        void main()
        {
            gl_Position = a_Position;
            gl_PointSize = 10.0;
            v_Color = a_Color; // Pass the data to the fragment shader
        }
    </script>

    <script type="x-shader/x-fragment" id="FragmentShader">
        precision mediump float; // Precision qualifier (See Chapter 6)

        varying vec4 v_Color; // Receive the data from the vertex shader

        void main()
        {
            gl_FragColor = v_Color;
        }
    </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>

JavaScript

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

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;
    }

    // Set the vertex information
    var n = initVertexBuffers(gl);
    if (n < 0)
    {
        console.log('Failed to set the vertex information');
        return;
    }

    // Specify the color for clearing <canvas>
    gl.clearColor(0.0, 0.0, 0.0, 1.0);

    // Clear <canvas>
    gl.clear(gl.COLOR_BUFFER_BIT);

    // Draw three points
    gl.drawArrays(gl.POINTS, 0, n);
}

function initVertexBuffers(gl)
{
    var verticesColors = new Float32Array([
      // Vertex coordinates and color
       0.0, 0.5, 1.0, 0.0, 0.0,
      -0.5, -0.5, 0.0, 1.0, 0.0,
       0.5, -0.5, 0.0, 0.0, 1.0,
    ]);
    var n = 3; // The number of vertices

    // Create a buffer object
    var vertexColorBuffer = gl.createBuffer();
    if (!vertexColorBuffer)
    {
        console.log('Failed to create...