ch10/Shadow

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>

    <!-- Vertex shader program for generating a shadow map -->
    <script type="x-shader/x-vertex" id="ShadowVertexShader">
        attribute vec4 a_Position;
        uniform mat4 u_MvpMatrix;

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

    <!-- Fragment shader program for generating a shadow map -->
    <script type="x-shader/x-fragment" id="ShadowFragmentShader">
        precision mediump float;

        void main()
        {
            // Write the z-value in R
            gl_FragColor = vec4(gl_FragCoord.z, 0.0, 0.0, 0.0);
        }
    </script>

    <!-- Vertex shader program for regular drawing -->
    <script type="x-shader/x-vertex" id="VertexShader">
        attribute vec4 a_Position;
        attribute vec4 a_Color;
        uniform mat4 u_MvpMatrix;
        uniform mat4 u_MvpMatrixFromLight;
        varying vec4 v_PositionFromLight;
        varying vec4 v_Color;

        void main()
        {
            gl_Position = u_MvpMatrix * a_Position;
            v_PositionFromLight = u_MvpMatrixFromLight * a_Position;
            v_Color = a_Color;
        }
    </script>

    <!-- Fragment shader program for regular drawing -->
    <script type="x-shader/x-fragment" id="FragmentShader">
        precision mediump float;

        uniform sampler2D u_ShadowMap;
        varying vec4 v_PositionFromLight;
        varying vec4 v_Color;

        void main()
        {
            vec3 shadowCoord = (v_PositionFromLight.xyz/v_PositionFromLight.w)/2.0 + 0.5;
            vec4 rgbaDepth = texture2D(u_ShadowMap, shadowCoord.xy);
            float depth = rgbaDepth.r; // Retrieve the z-value from R
            float visibility = (shadowCoord.z > depth + 0.005) ? 0.7 : 1.0;
            gl_FragColor = vec4(v_Color.rgb * visibility, v_Color.a);
        }
    </script>

    <script...

JavaScript

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

var OFFSCREEN_WIDTH = 2048, OFFSCREEN_HEIGHT = 2048;
var LIGHT_X = 0, LIGHT_Y = 7, LIGHT_Z = 2; // Position of the light source

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

// The increments of rotation angle (degrees)
var ANGLE_STEP = 40;

// 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 vShadowShaderElement = document.getElementById("ShadowVertexShader");
    var fShadowShaderElement = document.getElementById("ShadowFragmentShader");
    var vShaderElement = document.getElementById("VertexShader");
    var fShaderElement = document.getElementById("FragmentShader");
    if (vShadowShaderElement == null || vShadowShaderElement == null ||
        vShaderElement == null || fShaderElement == null)
    {
        console.log("Failed to get a shader element");
        return;
    }

    // Get shader sources
    var vShadowShaderSource = vShadowShaderElement.firstChild.textContent;
    var fShadowShaderSource = fShadowShaderElement.firstChild.textContent;
    var vShaderSource = vShaderElement.firstChild.textContent;
    var fShaderSource = fShaderElement.firstChild.textContent;

    // Initialize shaders for generating a shadow map
    var shadowProgram = createProgram(gl, vShadowShaderSource, fShadowShaderSource);
    shadowProgram.a_Position = gl.getAttribLocation(shadowProgram, 'a_Position');
    shadowProgram.u_MvpMatrix = gl.getUniformLocation(shadowProgram, 'u_MvpMatrix');
    if...