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

[Mason, Michael W]

> -----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;
   }

> 
> >> Please add both spec references in your patch.