三角与矩形

<script src="http://cdn.bootcss.com/jquery/2.1.4/jquery.js"></script>
<script src="http://cdn.bootcss.com/gl-matrix/2.2.1/gl-matrix.js"></script>

<div class="page-header"><h3>1、三角与矩形</h3></div>

<canvas id = "test01-canvas" width = "800" height = "600"></canvas>

<script id = "shader-fs" type = "x-shader/x-fragment">
    precision mediump float;
    void main(void)
    {
        gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
    }
</script>
<script id = "shader-vs" type = "x-shader/x-vertex">
    attribute vec3 aVertexPosition;
    uniform mat4 uMVMatrix;
    uniform mat4 uPMatrix;
    void main(void)
    {
        gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
    }
</script>

<script type="text/javascript">

$(document).ready(function ()
{
    webGLStart();
});

function webGLStart()
{
    var canvas = $("#test01-canvas")[0];
    initGL(canvas);
    initShaders();
    initBuffers();

    gl.clearColor(0.0, 0.0, 0.0, 1.0);
    gl.enable(gl.DEPTH_TEST);

    drawScene();
}

var gl;
function initGL(canvas)
{
    try
    {
        gl = canvas.getContext("webgl") || canvas.getContext("experimental-webgl");
        gl.viewportWidth = canvas.width;
        gl.viewportHeight = canvas.height;
    }catch(e){}
    if(!gl)
    {
        alert("无法初始化“WebGL”。");
    }
}

function getShader(gl, id)
{
    var shaderScript = $("#" + id);
    if(!shaderScript.length)
    {
        return null;
    }
    var str = shaderScript.text();

    var shader;
    if(shaderScript[0].type == "x-shader/x-fragment")
    {
        shader = gl.createShader(gl.FRAGMENT_SHADER);
    }
    else if(shaderScript[0].type == "x-shader/x-vertex")
    {
        shader = gl.createShader(gl.VERTEX_SHADER);
    }
    else
    {
        return null;
    }
    gl.shaderSource(shader, str);
    gl.compileShader(shader);
    if(!gl.getShaderParameter(shader, gl.COMPILE_STATUS))
    {
        alert(gl.getShaderInfoLog(shader));
        return null;
    }
    return shader;
}

var shaderProgram;
function initShaders()
{
    var fragmentShader = getShader(gl, "shader-fs");
    var vertexShader = getShader(gl, "shader-vs");
    shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);
    gl.linkProgram(shaderProgram);

    if(!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS))
    {
        alert("无法初始化“Shader”。");
    }
    gl.useProgram(shaderProgram);

    shaderProgram.vertexPositionAttribute = 
        gl.getAttribLocation(shaderProgram, "aVertexPosition");
    gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);

    shaderProgram.pMatrixUniform = 
        gl.getUniformLocation(shaderProgram, "uPMatrix");
    shaderProgram.mvMatrixUniform = 
        gl.getUniformLocation(shaderProgram, "uMVMatrix");
}


var mvMatrix = mat4.create();
var pMatrix = mat4.create();

function setMatrixUniforms()
{
    gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
    gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);
}


var triangleVertexPositionBuffer;
var squareVertexPositionBuffer;

function initBuffers()
{
    triangleVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexPositionBuffer);
    var vertices = [
                     0.0,  1.0,  0.0,
                    -1.0, -1.0,  0.0,
                     1.0, -1.0,  0.0
                     ];
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(vertices), gl.STATIC_DRAW);
    triangleVertexPositionBuffer.itemSize = 3;
    triangleVertexPositionBuffer.numItems = 3;

    squareVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
    vertices = [
                 1.0,  1.0,  0.0,
                -1.0,  1.0,  0.0,
                 1.0, -1.0,  0.0,
                -1.0, -1.0,  0.0
                ];
    gl.bufferData(gl.ARRAY_BUFFER, 
        new Float32Array(vertices), gl.STATIC_DRAW);
    squareVertexPositionBuffer.itemSize = 3;
    squareVertexPositionBuffer.numItems = 4;

}
function drawScene()
{
    gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    mat4.perspective(pMatrix, 45, 
        gl.viewportWidth / gl.viewportHeight, 0.1, 100.0);

    mat4.identity(mvMatrix);

    mat4.translate(mvMatrix, mvMatrix, [-1.5, 0.0, -7.0]);
    gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexPositionBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, 
        triangleVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
    setMatrixUniforms();
    gl.drawArrays(gl.TRIANGLES, 0, triangleVertexPositionBuffer.numItems);

    mat4.translate(mvMatrix, mvMatrix, [ 3.0, 0.0,  0.0]);
    gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, 
        squareVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
    setMatrixUniforms();
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, squareVertexPositionBuffer.numItems);
}
</script>