[Public WebGL] Null return values from create*

Gregg Tavares (勤) [email protected]
Thu Apr 5 17:11:33 PDT 2012


On Thu, Apr 5, 2012 at 4:46 PM, Glenn Maynard <[email protected]> wrote:

> On Thu, Apr 5, 2012 at 5:50 PM, Gregg Tavares (勤) <[email protected]> wrote:
>
>> The issue for me is, it seems like we're fixing createXXX because people
>> currently write code like this
>>
>> tex = gl.createTexture();
>> tex.url = urlOfImageImGoingToPutInTexture;  // crash
>>
>>
>> and that second line will fail if the context is lost. This type of
>> currently invalid code is all over learningwebgl.com :-(
>>
>> Well, that same problem exists with getUniformLocation and, as Glenn
>> pointed out in my own code, with getActiveAttrib and getActiveUniform.
>>
>
> Right, it can happen in a lot of places.  The reason we're focusing on the
> WebGLObject-creating functions right now is that there's a single,
> universal fix we can apply to all of them at once, without affecting any
> (non-pathological, at least) existing user code, since from the user's
> perspecitve, it just makes a particular rare case no longer happen.
>
> I agree that we should look at other functions and see if we can at least
> reduce the number of cases where they return null if the context is lost,
> but that'll become a case-by-case thing, so it's a lot more work.  This
> should probably happen in parallel to further fixing the nullable return
> values.  (For example, getSupportedExtensions should probably always return
> the last-known supported extensions, not null.)
>
> Many functions still have neither a nullable nor "any" return value, nor
> explicit context lost handling, which isn't valid.  A sample:
> getSupportedExtensions, getProgramInfoLog, getShaderPrecisionFormat,
> getShaderSource.  It's bad that it's so hard to detect these.  It would be
> a lot nicer if the "explicit context lost handling" was something we could
> annotate in WebIDL, eg. something like
>
> boolean isContextLost() annotate(explicit_context_loss=True);
>
> so these invalid cases could be detected automatically.  It might be
> useful for people generating bindings, too.
>
> +CC Cameron: Is there any way to do this now, or could something like this
> be added, so we can annotate functions with arbitrary, API-specific
> strings?  This would have no effect on the IDL; it would just be for
> API-specific flags.
>
>
>> For getUniformLocation it's certainly possible that people are attaching
>> things to the location object (though less common)
>>
>> var mvpLoc = gl.getUniformLocation(prg, "u_modelViewProjection");
>> mvpLoc.name = "u_modelViewProjection"  // crash
>>
>>
>> And of course getActiveAttrib and getActiveUniform are guaranteed to have
>> this problem.
>>
>> var info = getActiveAttrib(program, index);
>> if (info.size > 1 && endsWith(info.name, "[0]")) {  // crash
>>    ...
>> }
>>
>>
>> so all I'm saying is if we're trying to fix these issues shouldn't we fix
>> them everywhere?
>>
>> The thing is, even that won't save you. Lots of people do stuff this
>>
>
> This is still worth doing even if we can't do it everywhere; a 50%
> reduction in null-reference bugs is still an improvement, even if we can't
> reach 0% (which we probably can't, short of a broad switch to exceptions).
>
> On Thu, Apr 5, 2012 at 6:16 PM, Kenneth Russell <[email protected]> wrote:
>
>> As I see it, the main reason for changing the createXXX routines to
>> return non-null, invalidated objects after context loss is not really
>> to protect developers from dereferencing null.
>
>
> It's the main reason I suggested it (the nullable simplification is what
> made me think of it, but it's just a nice side-effect to me).  Returning
> null for errors, especially for rare errors, is one of the biggest source
> of obscure bugs in all languages.  It's not normally a problem in
> JavaScript--this is why everyone has switched to exceptions--but WebGL
> reintroduced it by using nulls.  I definitely wish WebGL had used
> exceptions like other APIs for synchronous errors like these (as we've
> discussed before), but if we can't fix that, then let's at least try to
> minimize the problem.
>

Wait what? How would exceptions help here? Is it even possible to use
exceptions AND get performance AND get no surprises during context lost?


>
>
>> There is definitely an argument that the current behavior is uniform.
>> Every entry point, including the creation entry points, can start
>> returning null essentially at any time. Also, if the behavior is
>> changed, the 1.0.1 conformance suite will no longer run on future
>> WebGL implementations, because it tests passing null for WebGLObjects
>> and expects that no exceptions are thrown.
>>
>
> "It'll break the test suite" is a very bad reason not to improve
> something.  Test suites are meant to improve APIs and implementations; if
> they're preventing us from improving them, they're doing the opposite.  We
> should only be concerned with whether a change improves the API, and what
> its web-compatibility effects are.  If it breaks the tests, then the tests
> get updated; that shouldn't be a consideration.
>
> --
> Glenn Maynard
>
>
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