webgl第29课-三维空间-模型视图矩阵

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上一节课我们学习了三维空间之加入旋转矩阵的三角形

这一节课我们将学习三维空间-模型视图矩阵

上节课你仔细看代码你会发现很多代码都是重复的，而且不适用大规模的顶点计算，这节课我们来优化优化一下，

先在JS中计算计算好矩阵，再给顶点着色器！

我们先来看下什么是模型视图矩阵：

运行结果也是一样：

具体看代码：

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <title>webgl第29课-三维空间-模型视图矩阵</title>
  </head>

  <body onload="main()">
    <canvas id="webgl" width="400" height="400">
    Please use a browser that supports "canvas"
    </canvas>

    <script src="../lib/webgl-utils.js"></script>
    <script src="../lib/webgl-debug.js"></script>
    <script src="../lib/cuon-utils.js"></script>
    <script src="../lib/cuon-matrix.js"></script>
    <script src="LookAtRotatedTriangles_mvMatrix.js"></script>
  </body>
</html>

// LookAtRotatedTriangles_modelViewMatrix.js (c) 2012 matsuda
// Vertex shader program
var VSHADER_SOURCE =
  'attribute vec4 a_Position;\n' +
  'attribute vec4 a_Color;\n' +
  'uniform mat4 u_ModelViewMatrix;\n' +
  'varying vec4 v_Color;\n' +
  'void main() {\n' +
  //这里是模型视图矩阵*顶点坐标
  '  gl_Position = u_ModelViewMatrix * a_Position;\n' +
  '  v_Color = a_Color;\n' +
  '}\n';

// Fragment shader program
var FSHADER_SOURCE =
  '#ifdef GL_ES\n' +
  'precision mediump float;\n' +
  '#endif\n' +
  'varying vec4 v_Color;\n' +
  'void main() {\n' +
  '  gl_FragColor = v_Color;\n' +
  '}\n';

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;
  }

  // Initialize shaders
  if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
    console.log('Failed to intialize shaders.');
    return;
  }

  // Set the vertex coordinates and color (the blue triangle is in the front)
  var n = initVertexBuffers(gl);
  if (n < 0) {
    console.log('Failed to set the vertex information');
    return;
  }

  // Specify the color for clearing <canvas>
  gl.clearColor(0.0, 0.0, 0.0, 1.0);

  // Get the storage location of u_ModelViewMatrix and u_ModelMatrix
  var u_ModelViewMatrix = gl.getUniformLocation(gl.program, 'u_ModelViewMatrix');
  if(!u_ModelViewMatrix) { 
    console.log('u_ModelViewMatrixの格納場所の取得に失敗');
    return;
  }

  // 设置视点，视线和上方向
  var viewMatrix = new Matrix4();
  viewMatrix.setLookAt(0.20, 0.25, 0.25, 0, 0, 0, 0, 1, 0);

  // Calculate matrix for rotate
  var modelMatrix = new Matrix4();
  modelMatrix.setRotate(-30, 0, 0, 1);

  // 2个矩阵相乘，事先在JS里面相乘
  var modelViewMatrix = viewMatrix.multiply(modelMatrix);

  // Pass the model view projection matrix
  gl.uniformMatrix4fv(u_ModelViewMatrix, false, modelViewMatrix.elements);

  // Clear <canvas>
  gl.clear(gl.COLOR_BUFFER_BIT);

  // Draw the rectangle
  gl.drawArrays(gl.TRIANGLES, 0, n);
}

function initVertexBuffers(gl) {//设置三角形相关数据并在main()中调用
  var verticesColors = new Float32Array([
    // 设置三角形的顶点坐标和颜色，为了更好的区分，本案例稍微修改了三角形的颜色
     0.0,  0.5,  -0.4,  0.4,  1.0,  0.4, // The back green one
    -0.5, -0.5,  -0.4,  0.4,  1.0,  0.4,
     0.5, -0.5,  -0.4,  0.4,  1.0,  0.4, 
   
     0.5,  0.4,  -0.2,  1.0,  0.4,  0.4, // The middle yellow one
    -0.5,  0.4,  -0.2,  1.0,  0.4,  0.4,
     0.0, -0.6,  -0.2,  1.0,  0.4,  0.4, 

     0.0,  0.5,   0.0,  0.4,  0.4,  1.0,  // The front blue one 
    -0.5, -0.5,   0.0,  0.4,  0.4,  1.0,
     0.5, -0.5,   0.0,  0.4,  0.4,  1.0, 
  ]);
  var n = 9;

  // 创建缓冲区对象、绑定、传值、启用等
  var vertexColorBuffer = gl.createBuffer();  
  if (!vertexColorBuffer) {
    console.log('Failed to create the buffer object');
    return -1;
  }

  // Write the vertex coordinates and color to the buffer object
  gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, verticesColors, gl.STATIC_DRAW);

  var FSIZE = verticesColors.BYTES_PER_ELEMENT;
  // Assign the buffer object to a_Position and enable the assignment
  var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
  if(a_Position < 0) {
    console.log('Failed to get the storage location of a_Position');
    return -1;
  }
  gl.vertexAttribPointer(a_Position, 3, gl.FLOAT, false, FSIZE * 6, 0);
  gl.enableVertexAttribArray(a_Position);
  // Assign the buffer object to a_Color and enable the assignment
  var a_Color = gl.getAttribLocation(gl.program, 'a_Color');
  if(a_Color < 0) {
    console.log('Failed to get the storage location of a_Color');
    return -1;
  }
  gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, FSIZE * 6, FSIZE * 3);
  gl.enableVertexAttribArray(a_Color);

  // Unbind the buffer object
  gl.bindBuffer(gl.ARRAY_BUFFER, null);

  return n;
}

webgl第29课-三维空间-模型视图矩阵

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