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Re: [Public WebGL] Ambiguity and Non-deterministicness in the WebGL Spec



On Dec 16, 2010, at 1:27 AM, Tim Johansson wrote:

>>> ...So I'd rewrite as "By default (what does that mean? ed) after compositing the contents of the drawing buffer are undefined but are guaranteed not to contain information from another process." Then add a non-normative note somewhere that "One way to an implementation can guarantee buffers do not contain information from another process is to clear the buffer to the default values specified in OpenGL ES."
>>> 
>>> This gives maximum flexibility to the implementation while maintaining security.
>> These words sound good. I have incorporated them into the spec in section 2.2.
>> 
> 
> Like I said in a previous mail I think this is a mistake. Leaving it undefined essentially means you will have to check what the most common implementations are doing and do the same thing. If you do anything else there is a high probability that content will not work since it relies on the behavior of the most common implementations.
> 
> Saying something is undefined does not mean implementations can choose to do whatever they want. If most desktop implementations keep the old value, which would be compliant with the spec and not very surprising since you need to be able to do that in the other mode, you can probably not make the optimizations you want on mobile without breaking content, even if you are still compliant with the spec.

I think it's a mistake to "over-spec" this feature just so every browser works the same. As I'm arguing in another thread, iOS uses a different rendering model that most desktop implementations. And I expect that other mobile platforms will have some differences as well. If we over-specify, it can lead to implementations having to do non-optimal things just to comply with the spec. 

I think in most cases the spec needs to be very rigorous in its compliance requirements. But in cases where performance is at stake I think it would be the bigger mistake to require exact compliance.

-----
~Chris
cmarrin@apple.com




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