[igt-dev] [PATCH v6 05/13] fb: Fix ARGB8888 color depth

[Ville Syrjälä]

On Wed, Sep 05, 2018 at 11:35:49AM +0200, Maxime Ripard wrote:
> On Fri, Aug 31, 2018 at 04:42:18PM +0300, Ville Syrjälä wrote:
> > On Fri, Aug 31, 2018 at 03:12:14PM +0200, Maxime Ripard wrote:
> > > The ARGB8888 has been listed as having a 32 bits depth, while it actually
> > > is a 24 bits format. Fix this.
> > 
> > I think 32 is the more usual definition for this.
> 
> Isn't color depth about the color itself? I guess alpha wouldn't apply
> in this case.

Not according to X at least.

  visual:
    visual id:    0x6d
    class:    TrueColor
    depth:    32 planes
    available colormap entries:    256 per subfield
    red, green, blue masks:    0xff0000, 0xff00, 0xff
    significant bits in color specification:    8 bits

Same for eg. drm_mode_legacy_fb_format().

> 
> In the same format list:
>   - RGB565 has a depth of 16
>   - XRGB8888 has a depth of 24
>   - XRGB2101010 has a depth of 30
>   - ARGB8888 has a depth of 32
> 
> Which seems to indicate that the list indeed meant that the color
> depth is about the color, and that ARGB8888 is wrong.

None of those other things have alpha, so they are still
consistent with the depth==32 definition for ARGB888.

-- 
Ville Syrjälä
Intel