571054 - emulate vertex attrib 0 on desktop GL

Status: RESOLVED FIXED

(Core :: Graphics: CanvasWebGL, defect)

Description

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

See "vertex attribute 0" at http://khronos.org/webgl/wiki/WebGL_and_OpenGL_Differences

We need to essentially create a dummy array of the appropriate size and bind it there, and we need to keep track of VertexAttrib[1234]* calls for attribute 0.

Comment 1

[Benoit Jacob [:bjacob] (mostly away)]

Attachment: Handle vertex attrib 0 on desktop GL

At long last, here it is.

Comment 2

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Comment on attachment 470578 [details] [diff] [review]
Handle vertex attrib 0 on desktop GL

Ack.. like we discussed, don't use a VBO; there's no reason to, and there's unnecessary overhead and complexity in creating/managing it.  Just create a client-side buffer (via new) and use glVertexAttribPointer directly with no VBO bound (0), and the only thing you have to do is restore the pointer and current VBO binding.

Looks good other than that (though keep the same indentation style in your new VertexAttrib* methods -- e.g. NS_IMETHODIMP on its own line, WebGLContext:: at the start of a new one etc.).

Comment 3

[Benoit Jacob [:bjacob] (mostly away)]

Attachment: Handle vertex attrib 0 on desktop GL, not using a VBO anymore

Right, here's the new version.

Comment 4

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Why make this so complicated?  It's unnecessary and premature optimization that complicates the code.  There's no need for a WebGLVector4f type, and there's no need to keep this vector around in between calls to optimize for using the same value.

float mAttrib0Value[4];
nsAutoArrayPtr<float> mVector;

mVector = new float[length * 4];
float *fp = &mVector[0];
for (int i = 0; i < length; ++i) {
  *fp++ = mAttrib0Value[0];
  *fp++ = mAttrib0Value[1];
  *fp++ = mAttrib0Value[2];
  *fp++ = mAttrib0Value[3];
}

vertexAttribPointer(... mVector);


And then after vertexAttribPointer has been reset, just

mVector = nsnull;

Comment 5

[Benoit Jacob [:bjacob] (mostly away)]

But keeping the buffer around had another use: it allowed to avoid doing a malloc() on every draw-call. We're talking about 16 bytes per vertex here, and a typical complex scene would draw 1e+6 vertices per second, so we're talking about avoiding a traffic of 1e+7 bytes malloc'd and free'd per second. Is that really negligible?

Comment 6

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Yes, because this situation will be extremely rare and easy to work around.  Assigning constants to vertex attrib 0 is very uncommon, and if the shader compiler happens to pick 0 for an attrib that you want a constant for (say, a color), you can use bindAttribLocation to force something like your vertex coords to be 0.

Comment 7

[Benoit Jacob [:bjacob] (mostly away)]

Attachment: Handle vertex attrib 0 on desktop GL, version 3

Here you go!

Comment 8

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Comment on attachment 470877 [details] [diff] [review]
Handle vertex attrib 0 on desktop GL, version 3

Looks good, thanks!

Comment 9

[Benoit Jacob [:bjacob] (mostly away)]

http://hg.mozilla.org/mozilla-central/rev/8d80930e10f3