# 三角与矩形

```html
<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>
```