[Mesa-dev] [PATCH] mesa: Fix render buffer initial internal format type

[Chad Versace]

Brian and Ian, me and Michael have a Mesa TLS question at the message's bottom.


On 01/13/2015 04:41 PM, Mason, Michael W wrote:
>> -----Original Message-----
>> From: Versace, Chad
>> Sent: Tuesday, January 13, 2015 3:42 PM
>> To: Mason, Michael W; mesa-dev at lists.freedesktop.org
>> Subject: Re: [Mesa-dev] [PATCH] mesa: Fix render buffer initial internal format type
>>
>> On 01/13/2015 02:34 PM, Mason, Michael W wrote:
>>>> -----Original Message-----
>>>> From: Versace, Chad
>>>> Sent: Tuesday, January 13, 2015 10:47 AM
>>>> To: Mason, Michael W; mesa-dev at lists.freedesktop.org
>>>> Subject: Re: [Mesa-dev] [PATCH] mesa: Fix render buffer initial
>>>> internal format type
>>>>
>>>> On 01/09/2015 05:21 PM, michael.w.mason at intel.com wrote:
>>>>> From: Mike Mason <michael.w.mason at intel.com>
>>>>>
>>>>> Changes the initial internal format of a render buffer to GL_RGBA4.
>>>>> This fixes a failure in the following DrawElements test:
>>>>>
>>>>> dEQP-GLES3.functional.state_query.rbo.renderbuffer_internal_format
>>>>> ---
>>>>>  src/mesa/main/renderbuffer.c | 6 +++++-
>>>>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/src/mesa/main/renderbuffer.c
>>>>> b/src/mesa/main/renderbuffer.c index 0bc7f2b..b339491 100644
>>>>> --- a/src/mesa/main/renderbuffer.c
>>>>> +++ b/src/mesa/main/renderbuffer.c
>>>>> @@ -53,7 +53,11 @@ _mesa_init_renderbuffer(struct gl_renderbuffer *rb, GLuint name)
>>>>>     rb->Width = 0;
>>>>>     rb->Height = 0;
>>>>>     rb->Depth = 0;
>>>>> -   rb->InternalFormat = GL_RGBA;
>>>>> +   /* Default internal format should be GL_RGBA4, per page 258,
>>>>> +    * table 6.15 of the GLES 3.0.4 spec. Same default is expected
>>>>> +    * in all OpenGL specs that support BindRenderbuffer().
>>>>> +    */
>>>>> +   rb->InternalFormat = GL_RGBA4;
>>>>>     rb->Format = MESA_FORMAT_NONE;
>>>>>  }
>>>>>
>>>>>
>>>> The patch needs to choose the initial internalformat based on the
>>>> context API.  Table 6.26 in the GL 3.3 Core spec says the initial
>>>> renderbuffer internalformat is GL_RGBA. Table 6.15 of the GLES 3.0 spec says GL_RGBA4.
>>>>
>>>> I think this is the correct logic:
>>>>
>>>>   if (_mesa_is_desktop_gl(ctx)) {
>>>>       rb->InternalFormat = GL_RGBA;
>>>>   } else {
>>>>       rb->InternalFormat = GL_RGBA4;
>>>>   }
>>>
>>> "ctx" isn't available in _mesa_init_renderbuffer (where this code resides) and GET_CURRENT_CONTEXT(ctx) gives nil for
>> ctx.  Is there any other way to get a pointer to the gl_context?
>>
>> Drivers call _mesa_init_renderbuffer for 3 reasons, as far as I can tell:
>>
>>     1. To initialize Mesa's gl_renderbuffer structure in response to a real GL
>>        renderbuffer object created with glGenRenderbuffers.
>>
>>     2. To initialize a driver-private renderbuffer in response of the user
>>        attaching a texture to a framebuffer object, such as with glFramebufferTexture2D.
>>
>>     3. To initialize a driver-private renderbuffer that serves as backing storage
>>        for window system surfaces, such as eglCreateWindowSurface or a GLX Window.
>>
>> Only in case 1 will the user have a handle to the renderbuffer object and be able to call glGetRenderbufferParameteriv on
>> it. In case 2, there is always a context present (I think...), but the driver will immediately overwrite the value of rb-
>>> InternalFormat anyway, so it doesn't really matter what value _mesa_init_renderbuffer chooses. In case 3, there may or
>> may not be a context present, but again the internalformat doesn't matter because the driver will immediately overwrite it.
>>
>> From that follows:
>>
>>     - If a context is current, we are in case 1 or 2. Case 1 is the more restrictive
>>       case. It requires that we select the internalformat based on the context's API.
>>
>>     - If a context is not current, we are in case 3, or possibly case 2 if I don't
>>       fully understand the problem space. Either way, in neither case 2 nor 3 does
>>       the value of internalformat matter, so we should just continue to initialize
>>       it to GL_RGBA as we have always done.
>>
> 
> So would something like this be safe?  Is ctx guaranteed to be either nil or a pointer to a valid context?
> 
>    GET_CURRENT_CONTEXT(ctx);
>    if (ctx && _mesa_is_gles3(ctx)) {
>       rb->InternalFormat = GL_RGBA4;
>    } else {
>       rb->InternalFormat = GL_RGBA;
>    }

Brian and Ian, _mesa_init_renderbuffer() sometimes gets called with a current context and
sometimes not, because it's used to initialize winsys renderbuffers. So me and Michael
have arrived at this question:

If no context is current, does Mesa guarantee that GET_CURRENT_CONTEXT(ctx) sets ctx = NULL?

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