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Re: [Public WebGL] using the same context with multiple canvases






On Wed, Dec 12, 2012 at 3:02 AM, Ian Hickson <ian@hixie.ch> wrote:
On Tue, 11 Dec 2012, Gregg Tavares (社ç~T¨) wrote:
>
> So to continue this discussion we still need to figure out what we plan to
> do for WebGL 1 context, multiple canvases
>
> IIRC the current thinking is this
>
>     gl = new WebGLRenderingContext();
>     db1 = new Drawingbuffer(creationAttributes1);
>     db2 = new Drawingbuffer(creationAttributes2);
>     canvas1 = document.createElement("canvas");
>     canvas2 = document.createElement("canvas");
>     canvas1.setDrawingbuffer(db1);
>     canvas2.setDrawingbuffer(db2);
>     gl.bindDrawingbuffer(db1);
>     gl.drawXXX(...);
>     gl.bindDrawingbuffer(db2);
>     gl.drawXXX(...);

I don't really understand what a drawing buffer is in this API.

Why wouldn't you just do:

   gl = new WebGLRenderingContext();
   canvas1.setContext(gl);
   gl.drawXXX(...);
   canvas2.setContext(gl);
   gl.drawXXX(...);


Because

 (1) your example is missing the creation attributes required for WebGL on setContext.

   (a) those should only be supplied once
   (b) as I pointed out they would be useful for canvas 2d as well

(2) we need a way to create drawing surfaces in Workers with creation parameters

 
...?

In any case, I think it can be made any number of ways, the only important
thing at this point to make sure it works consistently with the 2D context
and in particular to make sure it works in Worker threads is to use the
API described here:

   http://lists.w3.org/Archives/Public/public-whatwg-archive/2012Nov/0199.html

Specifically, the bit starting "it will require some additions to WebGL".

I still think that API needs to be informed by the decisions here. Specifically as I mentioned there is a desire for 2D canvases to have creation parameters similar to WebGL contexts. If nothing else to to be able to choose double buffered canvases (fast) vs the current single buffered canvases (slow)
 

HTH,
--
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
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