[Mesa-dev] MESA_EXTENSION_OVERRIDE problem

[Ian Romanick]

On 11/19/2015 12:30 PM, Ilia Mirkin wrote:
> On Thu, Nov 19, 2015 at 3:25 PM, Brian Paul <brianp at vmware.com> wrote:
>> On 11/19/2015 01:19 PM, Ilia Mirkin wrote:
>>> On Thu, Nov 19, 2015 at 3:13 PM, Brian Paul <brianp at vmware.com> wrote:
>>>>
>>>> Hi Nanley,
>>>>
>>>> Maybe you can fix an issue I have with the new extension code.
>>>>
>>>> Previously, I could do something like export
>>>> MESA_EXTENSION_OVERRIDE="-ARB_clear_buffer_object" and I would no longer
>>>> see
>>>> it in the GL_EXTENSIONS string, even if it was an "always on" extension.
>>>
>>> How sure are you that this worked?
>>
>> I'm pretty sure it worked that way when I first wrote it.
>>
>>> AFAIK there was no way to
>>> enable/disable an always-on ext.
>>
>> That's not the point.  The point is to change what
>> glGetString(GL_EXTENSIONS) (or the glGetStringi() method) returns to the
>> application.  I don't care if the underlying functionality is still working
>> in Mesa.  We're trying to tell the application to not use a feature.  I've
>> found this extremely helpful when debugging some apps.
>>
>>> That env var never affected the
>>> extension strings, but only the actual ctx->Extensions struct, which
>>> would indirectly modify the ext string. If the entry in that ext table
>>> was a dummy one, it had logic to not futz with it. (But it did so
>>> silently.)
>>
>> Yeah, I don't care about the table.  I only care about the return value of
>> glGetString(GL_EXTENSIONS).
> 
> I was pretty annoyed at that too -- having it affect exts returned by
> the driver seemed to be the important bit, but I think I investigated
> why it didn't work ~6 months ago, and came to the above conclusion
> [that it only futzed with the table]. In fact recently someone was
> unable to work around an ARB_dsa shortcoming in nouveau by disabling
> it with an override.

Ugh... How much should this work?  Extensions are used to determine GL
versions, and compute_version can't check that "always on" extensions
have been disabled.  If you try to disable GL_EXT_texture, you'll still
get at least OpenGL 1.1. :)  Is it okay that the version override is
still needed to disable newer versions?

> IMHO it makes sense for it to affect both the table and the ext
> string... i.e. if there's a ctx->Extensions.foo listed, it should turn
> that on/off, but if there isn't, it should still touch up the returned
> ext list.
> 
>   -ilia
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