ch10/Fog_w

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;
        uniform mat4 u_MvpMatrix;
        varying vec4 v_Color;
        varying float v_Dist;

        void main()
        {
            gl_Position = u_MvpMatrix * a_Position;

            v_Color = a_Color;

            // Use the negative z value of each vertex in view coordinate system
            v_Dist = gl_Position.w;
        }
    </script>

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

        uniform vec3 u_FogColor;    // Color of Fog
        uniform vec2 u_FogDist;     // Distance of Fog (starting
                                    // point, end point)
        varying vec4 v_Color;
        varying float v_Dist;

        void main()
        {
            // Calculation of fog factor (factor becomes smaller
            // as it goes further away from eye point)
            float fogFactor = clamp((u_FogDist.y - v_Dist) /
                            (u_FogDist.y - u_FogDist.x), 0.0, 1.0);

            // Stronger fog as it gets further: u_FogColor *
            // (1 - fogFactor) + v_Color * fogFactor
            vec3 color = mix(u_FogColor, vec3(v_Color),
                        clamp(fogFactor, 0.0, 1.0));

            gl_FragColor = vec4(color, v_Color.a);
        }
    </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

// Fog_w.js (c) 2012 matsuda and ohnishi
// 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 < 1)
    {
        console.log('Failed to set the vertex information');
        return;
    }

    // Color of Fog
    var fogColor = new Float32Array([0.137, 0.231, 0.423]);
    // Distance of fog [where fog starts, where fog completely covers object]
    var fogDist = new Float32Array([45, 80]);
    // Position of eye point (world coordinates)
    var eye = new Float32Array([25, 65, 35]);

    // Get the storage locations of uniform variables
    var u_MvpMatrix = gl.getUniformLocation(gl.program, 'u_MvpMatrix');
    var u_FogColor = gl.getUniformLocation(gl.program, 'u_FogColor');
    var u_FogDist = gl.getUniformLocation(gl.program, 'u_FogDist');
    if (!u_MvpMatrix || !u_FogColor || !u_FogDist)
    {
    ...