Question

我正在玩WebGL尝试学习它，所以我从webgl教程中获取了一些代码，并尝试添加自己的行，但每当我运行它时，它都会给我这个错误：

.WebGLRenderingContext: GL ERROR :GL_INVALID_OPERATION : glDrawElements: attempt to access out of range vertices in attribute 0

注意：属性0是我的顶点缓冲区

我的缓冲区初始化代码（如果没有定义，显然会假设全局变量）

    cubeVertexPositionBuffer = gl.createBuffer(); // create a buffer
gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);

//for laziness
var _f=1.0/3.0;

vertices = [ // this is code from the tutorial
// Front face
-1.0, -1.0, 1.0, 1.0, -1.0, 1.0, 1.0, 1.0, 1.0, -1.0, 1.0, 1.0,
// Back face
-1.0, -1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0, -1.0, 1.0, -1.0, -1.0,
// Top face
-1.0, 1.0, -1.0, -1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, -1.0,
// Bottom face
-1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, -1.0, 1.0, -1.0, -1.0, 1.0,
// Right face
1.0, -1.0, -1.0, 1.0, 1.0, -1.0, 1.0, 1.0, 1.0, 1.0, -1.0, 1.0,
// Left face
-1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0, -1.0, 1.0, -1.0, 

// this is my own code
-1.0+  _f, -1.0, 1.0,   -1.0+  _f, -1.0, -1.0,
-1.0+2*_f, -1.0, 1.0,   -1.0+2*_f, -1.0, -1.0,
-1.0+3*_f, -1.0, 1.0,   -1.0+3*_f, -1.0, -1.0,
-1.0+4*_f, -1.0, 1.0,   -1.0+4*_f, -1.0, -1.0,
-1.0+5*_f, -1.0, 1.0,   -1.0+5*_f, -1.0, -1.0


];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices),
        gl.STATIC_DRAW);
cubeVertexPositionBuffer.itemSize = 3;
cubeVertexPositionBuffer.numItems = 34;

    // color buffer code is irrelevant because my color buffer is attribute 1 not 0
    // plus it's all copied from the tutorial

    // index buffer 
    // note I changed some code so the cube drawn is wireframe instead of solid
    // I tested that without extra vertex or index buffer data and it worked
    cubeVertexIndexBuffer = gl.createBuffer(); // this modified a bit from the tutorial
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
cubeVertexIndices = 
    [ 0, 1, 2, 3, 0, // Front face 
      4, 5, 6, 7, 4, // Back face 
      8, 9, 10, 11, 8, // Top face 
      12, 13, 14, 15, 12, // Bottom face 
      16, 17, 18, 19, 16, // Right face 
      20, 21, 22, 23, 20, // Left face

      // this is my code
      24, 25, 26, 27, 28, 29, 30, 31, 32, 33
    ];
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(
        cubeVertexIndices), gl.STATIC_DRAW);
cubeVertexIndexBuffer.itemSize = 1;
cubeVertexIndexBuffer.numItems = 40;

这是我的绘图代码

// set up perspective and stuff
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
        cubeVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);

gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexColorBuffer);
gl.vertexAttribPointer(shaderProgram.vertexColorAttribute,
        cubeVertexColorBuffer.itemSize, gl.FLOAT, false, 0, 0);

gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);

gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix); // perspective matrix
gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix); // model view matrix

gl.lineWidth(1.0);
gl.drawElements(gl.LINES, cubeVertexIndexBuffer.numItems,
        gl.UNSIGNED_SHORT, 0);

Answer 1

其实我弄清楚了。作为我的WebGL新手，我设法忘记在我的颜色缓冲区中为每个顶点添加索引。我从未想到我的着色器需要每个顶点都有颜色。（如果WebGL说属性1（我的颜色属性）中的错误而不是属性0（我的顶点位置属性），那就太好了。

Answer 2

如果您在以下位置分配了bufferData，也会出现此问题：

gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(
    cubeVertexIndices), gl.STATIC_DRAW);

太短（参见第二个参数）。

如果以编程方式创建顶点，则会发生这种情况。至少，这就是发生在我身上的方式。

WebGL drawElements超出范围？

2 个答案: