[Public WebGL] WebGL back buffer contents

Tim Johansson [email protected]
Wed Jan 27 00:28:55 PST 2010


On 2010-01-27 01:45, Chris Marrin wrote:
> On Jan 26, 2010, at 3:37 PM, Oliver Hunt wrote:
>
>    
>> On Jan 26, 2010, at 3:28 PM, Chris Marrin wrote:
>>
>>      
>>> On Jan 26, 2010, at 10:00 AM, Vangelis Kokkevis wrote:
>>>
>>>        
>>>>
>>>> ...
>>>> I think we should settle on having the contents of the WebGL drawing
>>>> buffer be persistent, like the 2D context. Having a completely new
>>>> back buffer potentially swapped in unexpectedly will be too surprising
>>>> to the programmer.
>>>>
>>>> -Ken
>>>>
>>>> I like that idea although I'm not sure how we would handle resizing of drawing surface.  What's the expectation then?
>>>>          
>>> Here is what the Canvas element says:
>>>
>>> 	When the canvas element is created, and subsequently whenever the width and height attributes are
>>> 	set (whether to a new value or to the previous value), the bitmap and any associated contexts must
>>> 	be cleared back to their initial state and reinitialized with the newly specified coordinate space
>>> 	dimensions.
>>>
>>> 	When the canvas is initialized, its bitmap must be cleared to transparent black.
>>>
>>> That seems like an appropriate definition for us.
>>>        
>> My only concern with this exact definition is that the 2d canvas is completely reset - all state is clobbered, applying the same logic to webgl would imply that all shaders, etc would be unloaded as well, which seems a little extreme.
>>      
> Yeah, I didn't fully read the "and any associated contexts" part. I think that in the past we agreed that we should not even mess with the viewport coordinates on a size change. So perhaps better wording would be:
>
> 	When the canvas element is created, and subsequently whenever the width and height attributes are
> 	set (whether to a new value or to the previous value), the bitmap must be cleared to transparent black.
> 	Furthermore upon creation of the context its initial state shall be as described in the OpenGL ES 2.0
> 	specification [GLES20].
>
> 	Setting the width and height attributes after initialization shall not change the context state.
>
>    
I thought we said we should change the viewport when resizing, or maybe 
that changed later and I missed it?

I think it would be less confusing, at least in the most common case, if 
the viewport did change on resize.

//Tim

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