webgl第30课-用键盘来改变视点

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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-用键盘来改变视点

运行结果：

 

代码：

  
    
    
  

  
    
    Please use a browser that supports "canvas"
    

    
    
    
    
    
  

// 顶点着色器
var VSHADER_SOURCE =
  'attribute vec4 a_Position;\n' +
  'attribute vec4 a_Color;\n' +
  'uniform mat4 u_ViewMatrix;\n' +
  'varying vec4 v_Color;\n' +
  'void main() {\n' +
  '  gl_Position = u_ViewMatrix * a_Position;\n' +
  '  v_Color = a_Color;\n' +
  '}\n';

// 片元着色器
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  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 
  gl.clearColor(0, 0, 0, 1);

  //获取u ViewMatrix的存储位置
  var u_ViewMatrix = gl.getUniformLocation(gl.program, 'u_ViewMatrix');
  if(!u_ViewMatrix) { 
    console.log('Failed to get the storage locations of u_ViewMatrix');
    return;
  }

  // Create the view matrix
  var viewMatrix = new Matrix4();
  // 注册键盘事件响应函数
  document.onkeydown = function(ev){ keydown(ev, gl, n, u_ViewMatrix, viewMatrix); };

  draw(gl, n, u_ViewMatrix, viewMatrix);   // Draw
}

function initVertexBuffers(gl) {
  var verticesColors = new Float32Array([
    // Vertex coordinates and color
     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,  1.0,  0.4,  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,  1.0,  0.4,
     0.0, -0.6,  -0.2,  1.0,  1.0,  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,  1.0,  0.4,  0.4, 
  ]);
  var n = 9;

  // Create a buffer object
  var vertexColorbuffer = gl.createBuffer();  
  if (!vertexColorbuffer) {
    console.log('Failed to create the buffer object');
    return -1;
  }

  // Write the vertex information and enable it
  gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorbuffer);
  gl.bufferData(gl.ARRAY_BUFFER, verticesColors, gl.STATIC_DRAW);

  var FSIZE = verticesColors.BYTES_PER_ELEMENT;
  //Get the storage location of a_Position, assign and enable buffer
  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);  // Enable the assignment of the buffer object

  // Get the storage location of a_Position, assign buffer and enable
  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;
  }
  // Assign the buffer object to a_Color variable
  gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, FSIZE * 6, FSIZE * 3);
  gl.enableVertexAttribArray(a_Color);  // Enable the assignment of the buffer object

  return n;
}
//视点位置
var g_eyeX = 0.20, g_eyeY = 0.25, g_eyeZ = 0.25; // Eye position
//键盘事件函数
function keydown(ev, gl, n, u_ViewMatrix, viewMatrix) {
    if(ev.keyCode == 39) { // 按下右方向键
      g_eyeX += 0.01;
    } else 
    if (ev.keyCode == 37) { // 按下左方向键
      g_eyeX -= 0.01;
    } else { return; }// 其他直接返回
    draw(gl, n, u_ViewMatrix, viewMatrix);    
}
//绘制函数
function draw(gl, n, u_ViewMatrix, viewMatrix) {
  // Set the matrix to be used for to set the camera view
  viewMatrix.setLookAt(g_eyeX, g_eyeY, g_eyeZ, 0, 0, 0, 0, 1, 0);

  // Pass the view projection matrix
  gl.uniformMatrix4fv(u_ViewMatrix, false, viewMatrix.elements);

  gl.clear(gl.COLOR_BUFFER_BIT);     // Clear 

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