[Mesa-dev] [PATCH] Linking fails when not writing gl_Position.

[Kenneth Graunke]

On Tuesday, September 09, 2014 10:30:16 AM Ian Romanick wrote:
> On 09/08/2014 01:10 AM, Tapani Pälli wrote:
> > From: Kalyan Kondapally <kalyan.kondapally at intel.com>
> > 
> > According to GLSL-ES Spec(i.e. 1.0, 3.0), gl_Position value is undefined
> > after the vertex processing stage if we don't write gl_Position. However,
> > GLSL 1.10 Spec mentions that writing to gl_Position is mandatory. In case
> > of GLSL-ES, it's not an error and atleast the linking should pass.
> > Currently, Mesa throws an linker error in case we dont write to gl_position
> > and Version is less then 140(GLSL) and 300(GLSL-ES). This patch changes
> > it so that we don't report an error in case of GLSL-ES.
> 
> Wow.  We can add this to the list of ways OpenGL ES is just plain
> broken.  Since there is absolutely NO WAY this shader can produce any
> useful results, we should at least do the courtesy of generating a
> warning.  So, keep the first if-condistion the same, but do
> linker_warning instead of linker_error if prog->IsES.

I like that idea.  But what about 1.40 or 1.50?  I'm having a hard time imagining how 1.40 would let you produce any useful results, either (so maybe we should issue a warning there too).  With 1.50, you at least have geometry shaders, so you can produce real output later...

--Ken
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