webgl-utils.js

'use strict';

window.onerror = function(msg, url, lineno) {
    alert(url + '(' + lineno + '): ' + msg);
}

function createShader(str, type) {
    var shader = gl.createShader(type);
    gl.shaderSource(shader, str);
    gl.compileShader(shader);
    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        throw gl.getShaderInfoLog(shader);
    }
    return shader;
}

function createProgram(vstr, fstr) {
    var program = gl.createProgram();
    var vshader = createShader(vstr, gl.VERTEX_SHADER);
    var fshader = createShader(fstr, gl.FRAGMENT_SHADER);
    gl.attachShader(program, vshader);
    gl.attachShader(program, fshader);
    gl.linkProgram(program);
    if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
        throw gl.getProgramInfoLog(program);
    }
    return program;
}

function screenQuad() {
    var vertexPosBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, vertexPosBuffer);
    var vertices = [ -1, -1, 1, -1, -1, 1, 1, 1 ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
    vertexPosBuffer.itemSize = 2;
    vertexPosBuffer.numItems = 4;

    /*
      2___3
      |\  |
      | \ |
      |  \|
      0---1
    */

    return vertexPosBuffer;
}

function linkProgram(program) {
    var vshader = createShader(program.vshaderSource, gl.VERTEX_SHADER);
    var fshader = createShader(program.fshaderSource, gl.FRAGMENT_SHADER);
    gl.attachShader(program, vshader);
    gl.attachShader(program, fshader);
    gl.linkProgram(program);
    if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
        throw gl.getProgramInfoLog(program);
    }
}

function loadFile(file, callback, noCache, isJson) {
    var request = new XMLHttpRequest();
    request.onreadystatechange = function() {
        if (request.readyState == 1) {
            if (isJson) {
                request.overrideMimeType('application/json');
            }
            request.send();
        } else if (request.readyState == 4) {
            if (request.status == 200) {
                callback(request.responseText);
            } else if (request.status == 404) {
                throw 'File "' + file + '" does not exist.';
            } else {
                throw 'XHR error ' + request.status + '.';
            }
        }
    };
    var url = file;
    if (noCache) {
        url += '?' + Date.now();
    }
    request.open('GET', url, true);
}

function loadProgram(vs, fs, callback) {
    var program = gl.createProgram();
    function vshaderLoaded(str) {
        program.vshaderSource = str;
        if (program.fshaderSource) {
            linkProgram(program);
            callback(program);
        }
    }
    function fshaderLoaded(str) {
        program.fshaderSource = str;
        if (program.vshaderSource) {
            linkProgram(program);
            callback(program);
        }
    }
    loadFile(vs, vshaderLoaded, true);
    loadFile(fs, fshaderLoaded, true);
    return program;
}

(function() {
    var lastTime = 0;
    var vendors = ['ms', 'moz', 'webkit', 'o'];
    for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
        window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
        window.cancelRequestAnimationFrame = window[vendors[x]+
          'CancelRequestAnimationFrame'];
    }

    if (!window.requestAnimationFrame)
        window.requestAnimationFrame = function(callback, element) {
            var currTime = new Date().getTime();
            var timeToCall = Math.max(0, 16 - (currTime - lastTime));
            var id = window.setTimeout(function() { callback(currTime + timeToCall); },
              timeToCall);
            lastTime = currTime + timeToCall;
            return id;
        };

    if (!window.cancelAnimationFrame)
        window.cancelAnimationFrame = function(id) {
            clearTimeout(id);
        };
}())