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Re: [Public WebGL] Exceptions in WebGL



Resurrecting this thread to propose spec patch [1] to act on what
(seems to) have been agreed upon :
- use verb "generate" instead of "raise" for GL errors (not exceptions)

Additionally :
- for visual/semantic consistency, always use <code> with error names


Cheers,

[1] : http://neonux.com/webgl/errors-cleanup.patch.txt


On Thu, Apr 8, 2010 at 02:45, Kenneth Russell <kbr@google.com> wrote:
> On Tue, Apr 6, 2010 at 12:52 AM, Gregg Tavares <gman@google.com> wrote:
>>
>>
>> On Tue, Apr 6, 2010 at 6:08 AM, Kenneth Russell <kbr@google.com> wrote:
>>>
>>> On Mon, Apr 5, 2010 at 12:23 AM, Gregg Tavares <gman@google.com> wrote:
>>> > Maybe I'm skimming over it but it doesn't appear there is any language
>>> > in
>>> > the current spec about what WebGL functions should throw an exception
>>> > and
>>> > under what conditions even though every function is specified has able
>>> > to
>>> > throw one.
>>> >
>>> > for example.
>>> >
>>> > ctx.getActiveUniform(validProgram, invalidIndex);ÂÂ exception or
>>> > INVALID_VALUE?
>>> > ctx.getActiveUniform(null, 0);ÂÂ // This must be INVALID_VALUE but the
>>> > spec
>>> > doesn't stay
>>> > ctx.getActiveUniform(validProgramFromDifferenceContext, 0);Â //
>>> > exception or
>>> > INVALID_VALUE
>>> > ctx.getActiveUniform(deletedProgram, 0);Â // exception or INVALID_VALUE?
>>> > ctx.getActiveUniform(undefined, 0);Â // exception or INVALID_VALUE?
>>> > ctx.getActiveUniform(texture, 0);Â // exception or INVALID_OPERATION
>>> >
>>> > Pretty much every function has the same issues.
>>> >
>>> > Should this be nailed down? Am I just missing the section that covers
>>> > it?
>>>
>>> Earlier in the development of the WebGL spec it wasn't well defined
>>> which sorts of invalid inputs throw exceptions and which synthesize
>>> OpenGL errors. A few months ago after much discussion it was decided
>>> that the error handling would be unified to always synthesize OpenGL
>>> errors, and not throw exceptions. This unifies the error handling
>>> behavior and makes it easier to write things like debug GL wrappers
>>> which turn OpenGL errors into exceptions.
>>>
>>> The fact that the IDL still states that all of the entry points raise
>>> DOMException is basically an artifact. The best explanation for why
>>> this hasn't changed is so that the option is available in the future
>>> to throw DOMException if necessary.
>>>
>>> Some of the situations above (where you're passing an object of the
>>> wrong type) should be defined by Web IDL, I think, and should throw a
>>> SYNTAX_ERR DOMException. However, if the call makes it through the
>>> JavaScript binding, it should never throw an exception.
>>>
>>> -Ken
>>
>>
>> Sounds good.
>>
>> So that still brings up the question of what specific errors to synthesize
>> and adding these to the docs. For example.
>>
>> ctx.getActiveUniform(null, 0);
>>
>> This seems like it should generate INVALID_VALUE but some might argue for
>> INVALID_OPERATION. The argument for INVALID_VALUE is that's what the C api
>> would generate for an unknown value. The C api only generates
>> INVALID_OPERATION when the value passed in for program is something other
>> than a program. In WebGL that would raise an exception that a
>> non-WebGLProgram object was passed as the first parameter. On the other
>> hand, we know his is an invalid operation.
>
> I think this should generate INVALID_VALUE. Null is never a valid
> value to pass to this function. INVALID_OPERATION may imply that under
> different OpenGL state conditions, the given value might sometimes be
> valid.
>
>> ctx.getActiveUniform(validProgramFromDifferenceContext, 0);
>>
>> This one as well, INVALID_VALUE or INVALID_OPERATION. In the C api, again,
>> an unknown value would generate INVALID_VALUE and only passing in the ID of
>> something not a program would generate INVALID_OPERATION. On the other hand,
>> we know that it's an invalid operation to use a program from a different
>> context.
>
> I think this should generate INVALID_OPERATION. Future revisions of
> the WebGL specification will likely support sharing resources between
> WebGL contexts. In this case, if the contexts shared resources, the
> same program from a different context would be a valid argument to
> this call. Therefore the value isn't always invalid, so it should
> produce INVALID_OPERATION instead of INVALID_VALUE.
>
>> ctx.getActiveUniform(deletedProgram, 0);
>>
>> Same question. INVALID_OPERATION or INVALID_VALUE
>
> WebGL should match the C semantics here. I'm not sure based on reading
> the glGetActiveUniform man page which is produced. I suspect
> INVALID_VALUE.
>
>> ctx.getActiveUniform(undefined, 0);
>>
>> It's not clear to me if undefined converts to a value and should therefore
>> generate an error or undefined is marked at the WebIDL level as an
>> exception.
>
> I'm pretty sure Web IDL and the JavaScript bindings will convert
> undefined to NULL and not throw any exception.
>
>> ctx.getActiveUniform(texture, 0);
>>
>> This at least is clear. The WebIDL spec requires this to throw a TypeError
>> exception
>
> Agreed.
>
> -Ken
>
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