No subject

(Sorry if quoting the spec doesn't help, since you may have read it
already, but now that I looked up the relevant parts for the questions I
probably wouldn't formulate it much differently myself.)

"When interpolating variables declared using centroid in, the variable
is sampled at a location within the pixel covered by the primitive
generating the fragment."
"When interpolating variables declared using sample in when MULTISAMPLE
is enabled, the fragment shader will be invoked separately for each (!)
covered sample and the variable will be sampled at the corresponding
sample point."

> 
> Fourth question: how does gl_SampleMask interact with all that when
> more than one sample is evaluated.  And what does gl_SampleMaskIn look
> like in the same case?

"If the fragment shader is being evaluated at any frequency other than
per-fragment, bits of the sample mask not corresponding to the current
fragment shader invocation are ignored."

"When per-sample shading is active due to the use of a fragment input
qualified by sample, only the bit for the current sample is set in
gl_SampleMaskIn. When GL state specifies multiple fragment shader
invocations for a given fragment, the sample mask for any single
fragment shader invocation may specify a subset of the covered samples
for the fragment. In this case, the bit corresponding to each covered
sample will be set in exactly one fragment shader invocation."

> 
> I hope you people can help me clarify all that stuff :-)
> 
> Best,
> 
>   OG.
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