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Re: [Public WebGL] Some WebGL draft feedback
On Dec 23, 2009, at 2:04 PM, Tim Johansson wrote:
On 12/23/09 11:53 AM, Gregg Tavares wrote:
The opera-2dgame context was something I added because it was
required to move some demos we had in a technology similar to
<canvas> to <canvas>. It does not say much about the intent of the
Having more than one context has apparently been around since 2006
And the HTML5 spec certainly doesn't discourage multiple contexts
It seems like that's the design they intended as it's by far the
Almost all of the functionality of that context has since been added
to the main 2d context.
The only reliable way I see of doing that is to have some kind of
present function which copies the pixels to the <canvas>. Doing that
would make writing webgl content more complicated and potentially
make it much harder to write an implementation which performs well.
That suggests a few different paths
1) Support multiple contexts including webgl.
I certainly understand the issues here though it wouldn't be all
that hard to implement it in such a way that there is no
performance penalty if not used. WebGL already has to support
canvas.toDataURL so the code to support that could easily be called
if a draw function in a different context is used and visa-versa.
It might be OK for us to drop opera-2dgame if it is not widely used,
have to check that though. Most of the functionality from
opera-2dgame is in 2d anyway.
2) Don't support multiple contexts.
That seems like bad choice given that there is already precedent
and it's extremely useful. If canvas is by design, a bucket of
pixels then it certainly makes sense that it would be possible to
effect those pixels in multiple ways and as more ways come up use
them all together.
It would also be possible to distinguish between "main" contexts and
"extension" contexts and just not allow multiple "main" contexts. I
would say opera-2dgame is an extension to 2d.
Thanks, Tim. Ok, so it sounds like opera-2dgame is really just an
extension to the 2d context. So that makes it reasonable to use both
contexts to render to the canvas at the same time. The same can't be
said for 2D vs WebGL. The API's are radically different and mixing API
calls on many platforms can be difficult or impossible. More on that
in my response to Gregg's post.
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