“无法读取未定义的属性‘投影’”：我的第一个 3D 几何程序中的 webgl 错误

Question

我正在查看 webglfundamentals 博客系列和学习动画。根据我的理解，我试图以稍微不同的方式复制this，这样我就不会依赖于博客系列的 util 文件。我无法解决此错误：

Cannot read property 'projection' of undefined
    at createVertices.

var gl,
    shaderProgram,
    vertices;

initGL();
createShaders();
createVertices();

function initGL() {
  var canvas = document.getElementById("canvas");
  console.log(canvas);
  gl = canvas.getContext("webgl");
  gl.viewport(0, 0, canvas.width, canvas.height);
  gl.clearColor(1, 1, 1, 1);
}

function createShaders() {
  var vertexShader = getShader(gl, "3d-vertex-shader");
  var fragmentShader = getShader(gl, "3d-fragment-shader");
  
  shaderProgram = gl.createProgram();
  gl.attachShader(shaderProgram, vertexShader);
  gl.attachShader(shaderProgram, fragmentShader);
  gl.linkProgram(shaderProgram);

}

function createVertices() {
  vertices = [
   // left column
            0,   0,  0,
           30,   0,  0,
            0, 150,  0,
            0, 150,  0,
           30,   0,  0,
           30, 150,  0,
 
          // top rung
           30,   0,  0,
          100,   0,  0,
           30,  30,  0,
           30,  30,  0,
          100,   0,  0,
          100,  30,  0,
 
          // middle rung
           30,  60,  0,
           67,  60,  0,
           30,  90,  0,
           30,  90,  0,
           67,  60,  0,
           67,  90,  0
  ];
   

  
  //create buffer
  var buffer = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
  
  
  function radToDeg(r) {
    return r * 180 / Math.PI;
  }

  function degToRad(d) {
    return d * Math.PI / 180;
  }

  var translation = [45, 150, 0];
  var rotation = [degToRad(40), degToRad(25), degToRad(325)];
  var scale = [1, 1, 1];
  var color = [Math.random(), Math.random(), Math.random(), 1];
  
  
  
  // look up where the vertex data needs to go.
  var positionLocation = gl.getAttribLocation(shaderProgram, "a_position");

  // lookup uniforms
  var colorLocation = gl.getUniformLocation(shaderProgram, "u_color");
  var matrixLocation = gl.getUniformLocation(shaderProgram, "u_matrix");
  
   
   // webglUtils.resizeCanvasToDisplaySize(gl.canvas);

    // Tell it to use our program (pair of shaders)
    gl.useProgram(shaderProgram);

    // Turn on the attribute
    gl.enableVertexAttribArray(positionLocation);
  
    // Create a buffer to put positions in
    var positionBuffer = gl.createBuffer();
    // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
    gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

    // Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER)
    var size = 3;          // 3 components per iteration
    var type = gl.FLOAT;   // the data is 32bit floats
    var normalize = false; // don't normalize the data
    var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
    var offset = 0;        // start at the beginning of the buffer
    gl.vertexAttribPointer(
        positionLocation, size, type, normalize, stride, offset)

    // set the color
    gl.uniform4fv(colorLocation, color);

    // Compute the matrices
    var matrix = m4.projection(gl.canvas.clientWidth, gl.canvas.clientHeight, 400);
    matrix = m4.translate(matrix, translation[0], translation[1], translation[2]);
    matrix = m4.xRotate(matrix, rotation[0]);
    matrix = m4.yRotate(matrix, rotation[1]);
    matrix = m4.zRotate(matrix, rotation[2]);
    matrix = m4.scale(matrix, scale[0], scale[1], scale[2]);

    // Set the matrix.
    gl.uniformMatrix4fv(matrixLocation, false, matrix);

    // Draw the geometry.
    var primitiveType = gl.TRIANGLES;
    var offset = 0;
    var count = 18;  // 6 triangles in the 'F', 3 points per triangle
    gl.drawArrays(primitiveType, offset, count);
}

//m4 
var m4 = {

  projection: function(width, height, depth) {
    // Note: This matrix flips the Y axis so 0 is at the top.
    return [
       2 / width, 0, 0, 0,
       0, -2 / height, 0, 0,
       0, 0, 2 / depth, 0,
      -1, 1, 0, 1,
    ];
  },

  multiply: function(a, b) {
    var a00 = a[0 * 4 + 0];
    var a01 = a[0 * 4 + 1];
    var a02 = a[0 * 4 + 2];
    var a03 = a[0 * 4 + 3];
    var a10 = a[1 * 4 + 0];
    var a11 = a[1 * 4 + 1];
    var a12 = a[1 * 4 + 2];
    var a13 = a[1 * 4 + 3];
    var a20 = a[2 * 4 + 0];
    var a21 = a[2 * 4 + 1];
    var a22 = a[2 * 4 + 2];
    var a23 = a[2 * 4 + 3];
    var a30 = a[3 * 4 + 0];
    var a31 = a[3 * 4 + 1];
    var a32 = a[3 * 4 + 2];
    var a33 = a[3 * 4 + 3];
    var b00 = b[0 * 4 + 0];
    var b01 = b[0 * 4 + 1];
    var b02 = b[0 * 4 + 2];
    var b03 = b[0 * 4 + 3];
    var b10 = b[1 * 4 + 0];
    var b11 = b[1 * 4 + 1];
    var b12 = b[1 * 4 + 2];
    var b13 = b[1 * 4 + 3];
    var b20 = b[2 * 4 + 0];
    var b21 = b[2 * 4 + 1];
    var b22 = b[2 * 4 + 2];
    var b23 = b[2 * 4 + 3];
    var b30 = b[3 * 4 + 0];
    var b31 = b[3 * 4 + 1];
    var b32 = b[3 * 4 + 2];
    var b33 = b[3 * 4 + 3];
    return [
      b00 * a00 + b01 * a10 + b02 * a20 + b03 * a30,
      b00 * a01 + b01 * a11 + b02 * a21 + b03 * a31,
      b00 * a02 + b01 * a12 + b02 * a22 + b03 * a32,
      b00 * a03 + b01 * a13 + b02 * a23 + b03 * a33,
      b10 * a00 + b11 * a10 + b12 * a20 + b13 * a30,
      b10 * a01 + b11 * a11 + b12 * a21 + b13 * a31,
      b10 * a02 + b11 * a12 + b12 * a22 + b13 * a32,
      b10 * a03 + b11 * a13 + b12 * a23 + b13 * a33,
      b20 * a00 + b21 * a10 + b22 * a20 + b23 * a30,
      b20 * a01 + b21 * a11 + b22 * a21 + b23 * a31,
      b20 * a02 + b21 * a12 + b22 * a22 + b23 * a32,
      b20 * a03 + b21 * a13 + b22 * a23 + b23 * a33,
      b30 * a00 + b31 * a10 + b32 * a20 + b33 * a30,
      b30 * a01 + b31 * a11 + b32 * a21 + b33 * a31,
      b30 * a02 + b31 * a12 + b32 * a22 + b33 * a32,
      b30 * a03 + b31 * a13 + b32 * a23 + b33 * a33,
    ];
  },

  translation: function(tx, ty, tz) {
    return [
       1,  0,  0,  0,
       0,  1,  0,  0,
       0,  0,  1,  0,
       tx, ty, tz, 1,
    ];
  },

  xRotation: function(angleInRadians) {
    var c = Math.cos(angleInRadians);
    var s = Math.sin(angleInRadians);

    return [
      1, 0, 0, 0,
      0, c, s, 0,
      0, -s, c, 0,
      0, 0, 0, 1,
    ];
  },

  yRotation: function(angleInRadians) {
    var c = Math.cos(angleInRadians);
    var s = Math.sin(angleInRadians);

    return [
      c, 0, -s, 0,
      0, 1, 0, 0,
      s, 0, c, 0,
      0, 0, 0, 1,
    ];
  },

  zRotation: function(angleInRadians) {
    var c = Math.cos(angleInRadians);
    var s = Math.sin(angleInRadians);

    return [
       c, s, 0, 0,
      -s, c, 0, 0,
       0, 0, 1, 0,
       0, 0, 0, 1,
    ];
  },

  scaling: function(sx, sy, sz) {
    return [
      sx, 0,  0,  0,
      0, sy,  0,  0,
      0,  0, sz,  0,
      0,  0,  0,  1,
    ];
  },

  translate: function(m, tx, ty, tz) {
    return m4.multiply(m, m4.translation(tx, ty, tz));
  },

  xRotate: function(m, angleInRadians) {
    return m4.multiply(m, m4.xRotation(angleInRadians));
  },

  yRotate: function(m, angleInRadians) {
    return m4.multiply(m, m4.yRotation(angleInRadians));
  },

  zRotate: function(m, angleInRadians) {
    return m4.multiply(m, m4.zRotation(angleInRadians));
  },

  scale: function(m, sx, sy, sz) {
    return m4.multiply(m, m4.scaling(sx, sy, sz));
  },

};
// m4 ends


  /*
   * https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API/Tutorial/Adding_2D_content_to_a_WebGL_context
   */
  function getShader(gl, id) {
    var shaderScript, theSource, currentChild, shader;

    shaderScript = document.getElementById(id);

    if (!shaderScript) {
      return null;
    }

    theSource = "";
    currentChild = shaderScript.firstChild;

    while (currentChild) {
      if (currentChild.nodeType == currentChild.TEXT_NODE) {
        theSource += currentChild.textContent;
      }

      currentChild = currentChild.nextSibling;
    }
    if (shaderScript.type == "x-shader/x-fragment") {
      shader = gl.createShader(gl.FRAGMENT_SHADER);
    } else if (shaderScript.type == "x-shader/x-vertex") {
      shader = gl.createShader(gl.VERTEX_SHADER);
    } else {
      // Unknown shader type
      return null;
    }
    gl.shaderSource(shader, theSource);

// Compile the shader program
    gl.compileShader(shader);

// See if it compiled successfully
    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
      alert("An error occurred compiling the shaders: " + gl.getShaderInfoLog(shader));
      return null;
    }

    return shader;
  }

<canvas id="canvas"></canvas>


<!-- vertex shader -->
<script id="3d-vertex-shader" type="x-shader/x-vertex">
attribute vec4 a_position;

uniform mat4 u_matrix;

void main() {
  // Multiply the position by the matrix.
  gl_Position = u_matrix * a_position;
}
</script>
<!-- fragment shader -->
<script id="3d-fragment-shader" type="x-shader/x-fragment">
precision mediump float;

uniform vec4 u_color;

void main() {
   gl_FragColor = u_color;
}
</script>
<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See http://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and http://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="https://webglfundamentals.org/webgl/resources/webgl-utils.js"></script>
<script src="https://webglfundamentals.org/webgl/resources/webgl-lessons-ui.js"></script>
<script src="https://webglfundamentals.org/webgl/resources/webgl-lessons-helper.js"></script>

我的笔是here.

如果有人能帮我解决这个错误，那就太好了。

Answer 1

错误信息

无法读取 createVertices 处未定义的属性“投影”。

表示projection 在您尝试使用时未定义。这是因为m4.projection是稍后在脚本中定义的。

要解决这个问题，你应该在脚本的开头做声明，在结尾做函数调用。
将以下代码移到脚本的最前面：

initGL();
createShaders();
createVertices();

当你这样做时，你会得到下一个错误：

GL ERROR :GL_INVALID_OPERATION : glDrawArrays: 尝试访问属性 0 中超出范围的顶点

这是因为当你调用

gl.drawArrays(primitiveType, offset, count);

当前的 ARRAY_BUFFER 是 positionBuffer，它是空的。我假设你想绑定buffer。
删除以下行来解决这个问题：

var positionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);