[Mesa-dev] [shader-db PATCH 1/5] run: create debug contexts

[Matt Turner]

On Thu, Dec 31, 2015 at 12:25 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Thu, Dec 31, 2015 at 12:17 PM, Matt Turner <mattst88 at gmail.com> wrote:
>> On Thu, Dec 31, 2015 at 9:45 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>> On Dec 31, 2015 9:32 AM, "Matt Turner" <mattst88 at gmail.com> wrote:
>>>>
>>>> On Wed, Dec 30, 2015 at 9:32 PM, Nicolai Hähnle <nhaehnle at gmail.com>
>>>> wrote:
>>>> > For Gallium-based drivers, this is required for receiving shader
>>>> > information
>>>> > via debug messages.
>>>> > ---
>>>>
>>>> But that's a Gallium bug, right?
>>>>
>>>> Ilia sent a similar patch, and in the discussion I think we decided
>>>> that what run.c is doing is perfectly fine.
>>>
>>> It's not a bug at all. Behavioural difference from i965 though. I was happy
>>> to let the matter drop as I was the sole user of it. Sounds like there are
>>> going to be more now, so this has to be addressed one way or the other.
>>
>> Could you summarize what that difference is?
>
> Sure. i965 always generates messages to be sent to KHR_debug
> (potentially restricted by some env vars as well). st/mesa only passes
> the callback info through for GL debug contexts. The drivers, in turn,
> can use the presence/absence of the callback as an indicator as to
> whether to perform extra work. Mildly relatedly, currently GL context
> flags are not made available in pipe contexts.

Okay, I checked the spec again:

    Debug output functionality is controlled with the DEBUG_OUTPUT enable
    state. If the context is created with the CONTEXT_FLAG_DEBUG_BIT set then
    the initial state of DEBUG_OUTPUT is TRUE, otherwise the initial state of
    DEBUG_OUTPUT is FALSE. In a debug context, if DEBUG_OUTPUT is disabled the
    GL will not generate any debug output logs or callbacks. Enabling
    DEBUG_OUTPUT again will enable full debug output functionality. If the
    context was created without the CONTEXT_FLAG_DEBUG_BIT and the
    DEBUG_OUTPUT is later enabled, the level of debug output logging is
    defined by the GL implementation, which may have zero debug output. To
    guarantee the full debug output support of the GL implementation the
    context should be created with CONTEXT_FLAG_DEBUG_BIT context flag bit
    set.

I was somewhat surprised to see that it is implementation-defined
whether *any* debugging information gets out if a debug context is not
created.

I'd rather that the "implementation" be "Mesa" and not "i965" or "Gallium".

Ian, Timothy, others: Are other people okay with changing core-Mesa to
not emit any debug messages if not in a debug context?

This would mean that, even if the program has called
glEnable(GL_DEBUG_OUTPUT), if not in a debug context there are no
debug messages. This is apparently the route Gallium is taking.