[Mesa-dev] [PATCH v2] mesa: Fix swizzling for luminance/intensity in _mesa_readpixels

[Chris Wilson]

Quoting Chris Wilson (2017-07-31 22:51:25)
> Luminance/Intensity when converted to RGB should be replicated to fill
> the RGB channels, but they differ on how the alpha channel is filled, as
> luminance is set to 1 (unless alpha is supplied) and intensity is
> replicated into alpha as well.
> 
> https://www.khronos.org/opengl/wiki/Image_Format:
> 
>     Legacy Image Formats
> 
>     Warning: This section describes legacy OpenGL APIs that have been
>     removed from core OpenGL 3.1 and above (they are only deprecated in
>     OpenGL 3.0). It is recommended that you not use this functionality in
>     your programs.
> 
>     As with other deprecated functionality, it is advised that you not rely
>     on these features.
> 
>     Luminance and intensity formats are color formats. They are one or two
>     channel formats like RED or RG, but they specify particular behavior.
> 
>     When a GL_RED format is sampled in a shader, the resulting vec4 is (Red,
>     0, 0, 1). When a GL_INTENSITY format is sampled, the resulting vec4 is
>     (I, I, I, I). The single intensity value is read into all four
>     components. For GL_LUMINANCE, the result is (L, L, L, 1). There is also
>     a two-channel GL_LUMINANCE_ALPHA format, which gives (L, L, L, A).
> 
> v2: luminance -> xxx1, intensity -> xxxx, luminance_alpha -> xxxw

If that quote is the expected behaviour for glReadPixels and
glGetTexSubImage, there's a similar stanza to fix in texgetimage.c
(As well as the piglit tests to update.)

With a quick grep through VK-GL-CTS I didn't anything to refer to.
-Chris