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Re: [Public WebGL] ANGLE_instanced_arrays extension proposal





----- Original Message -----
> On Tue, Mar 6, 2012 at 4:01 PM, Florian BÃsch <pyalot@gmail.com>
> wrote:
> > On Wed, Mar 7, 2012 at 12:57 AM, John Bauman <jbauman@chromium.org>
> > wrote:
> >>
> >> If you want you could do that only on the first instanced draw
> >> from a
> >> buffer, and keep a shadow copy afterwards, but it might be
> >> difficult to make
> >> that perform well.
> >
> > No nead for readbacks, if you intercept bufferData calls and create
> > a shadow
> > copy then which you manage, you can do the right thing once before
> > draw.
> 
> This implies that the WebGL implementation maintains a copy of all
> vertex data that's been uploaded. As I mentioned above I think this
> is
> impractical on mobile devices.

Not just on mobile devices, but on desktop too, given that our desktop users care about memory usage too.

In Firefox, you can see how much (video) memory WebGLBuffers use by going to about:memory, and scrolling down to webgl-buffer-memory. It's often large enough that we'd need a very good reason to keep a copy of it on the heap. For example, this simple Quake3 level renderer,
    http://media.tojicode.com/q3bsp/
uses 1.66 MB of buffer data, and that's just an idle empty level.

Opera's Odin demo,
    http://operasoftware.github.com/Odin/demo.html
uses 2.05 MB of buffer data, with just one animated character and some objects around it.

Benoit

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