Re: [Public WebGL] WebGLArray iterator proposal

[Patrick Baggett <baggett.patrick@gmail.com>]

My understanding was that the constructors would create a copy of the buffer:

5.13.3.1 Shared Constructors

Constructor(array)
Create a new WebGLTypeNameArray object with a new underlying
            WebGLArrayBuffer large enough to hold the given data, then 
copy the passed
            data into the buffer.
        

If so, that kills your example. =(

If not, I think the wording on 5.13.3.1 needs to be seriously changed.

Patrick Baggett

On Sun, Jan 10, 2010 at 3:25 AM, Kenneth Russell <kbr@google.com> wrote:

A crucial piece you're missing is the fact that multiple WebGLArrays can refer to the same region of memory. To do so, use the WebGL[T]Array constructor taking a WebGLArrayBuffer. You can either create the WebGLArrayBuffer separately, or fetch it from a previously created WebGLArray.

To implement your first example, you would do something like

  var numVertices = 100; // for example

  var floatSize = gl.sizeInBytes(gl.FLOAT);

  var vertexSize = 3 * floatSize + 4 * gl.sizeInBytes(gl.UNSIGNED_BYTE);

  // Round up to sizeInBytes(gl.FLOAT) -- just in case it isn't 4 on some platforms

  vertexSize = ((vertexSize + floatSize - 1) / floatSize) * floatSize;

  var vertexSizeInFloats = vertexSize / floatSize;

  var buf = new WebGLArrayBuffer(numVertices * vertexSize);

  var floatArray = new WebGLFloatArray(buf);

  var byteArray = new WebGLUnsignedByteArray(buf);

  var floatIdx = 0;

  // Set up the initial offset of the bytes within the vertex data

  var byteIdx = 3 * floatSize;

  for (var i = 0; i < numVertices; i++) {

    floatArray[floatIdx] = ...;

    floatArray[floatIdx + 1] = ...;

    floatArray[floatIdx + 2] = ...;

    byteArray[byteIdx] = ...;

    byteArray[byteIdx + 1] = ...;

    byteArray[byteIdx + 2] = ...;

    byteArray[byteIdx + 3] = ...;

    floatIdx += vertexSizeInFloats;

    byteIdx += vertexSize;

  }

We certainly need to provide examples of this. Right now I don't think there are any examples of heterogeneous interleaved data in the demos.

You should be able to implement the sort of iterators you have in mind in pure _javascript_, hiding these details from the casual programmer. Please take another look at the spec and give it a try.

-Ken