WebGL drawElements out of range?

Question

I am playing around with WebGL trying to learn it, so I took some code from a webgl tutorial, and tried to add my own lines, but whenever I run it, it gives me this error:

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

Note: attribute 0 is my vertex buffer

My buffer initialization code is (obviously assume global vars if there is no definition)

    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;

And here's my drawing code

// 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

Actually I figured it out. Being the WebGL newb that I am, I managed to forget to add the indexes for each vertex in my color buffer. It just never came across my mind that my shaders required each vertex to have a color. (It would have been nice though, if WebGL had said it was an error in attribute 1 (my color attribute) and not attribute 0 (my vertex position attribute).

Answer 2

The problem can also occur if the bufferData you have allocated in:

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

is too short (See second parameter).

This can happen if the creation of vertices happen programmatically. At least, that's the way it happened to me.