[Public WebGL] Why does the set of pname arguments for which the behavior of getShaderParameter is defined not match GL ES?

Glenn Maynard [email protected]
Tue Apr 17 21:16:16 PDT 2012


On Tue, Apr 17, 2012 at 10:56 PM, Boris Zbarsky <[email protected]> wrote:

>  Constant values not mentioned in the spec should always be invalid
>>
>
> Saying that in a normative statement somewhere would cover this case, yes.
>  Makes for slightly confusing reading, of course, given the spec's "defer
> to ES" general structure: you have to know that you're supposed to defer to
> ES except in these various cases which are defined somewhere far far away
> from the definition of the actual method you're implementing....


It could be specified in each function that takes an enum argument, eg.
replace the getShaderParameter definition with something like:

"If *pname* is not present in the following table, generate
GL_INVALID_ENUM.  Otherwise, return the value for *pname* given *shader*,
using the specified type."

This makes it explicit that only the listed enums are supported, puts that
requirement where it'll be seen (in the function definition), and is brief
enough that this language can be used in all functions like this.

(That language is a little awkward, and can probably be improved a bit.)

 It's probably worth having tests to make sure the typical underlying
>> constants for those intentionally-unsupported enums are actually
>> disallowed, at least.
>>
>
> Yes, like every normative requirement.
>

Not exactly: to test this fully, you'd need to test every value which isn't
explicitly supported.  (For example, ES extensions might add enums to these
tables beyond those in the core spec.  With WebGL, that is only permitted
if the extension is explicitly enabled with getExtension.)  That would make
for unreasonably expensive tests.

It's probably reasonable to test every unsupported [0, 0xFFFF] value,
though, for every function that takes an enum.

-- 
Glenn Maynard
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