[Mesa-dev] [PATCH] i965/blorp: Fix hw blending coefficients

[Pohjolainen, Topi]

On Mon, Feb 03, 2014 at 11:30:58AM -0800, Eric Anholt wrote:
> Topi Pohjolainen <topi.pohjolainen at intel.com> writes:
> 
> > Previously the color components where evaluated using formula
> > (src_color * src_color + 1.0 dst_color) and alpha in turn using
>                            ^ 0.0
> > (1.0 * src_alpha + 0.0 * dst_alpha). The intention is to keep
> > source color components unmodified and force alpha channel to
> > fixed value of one regardless of source or destination.
> 
> Not multiplying the source color by source color makes a lot of sense.
> But your CONSTANT_ALPHA with ALPHA of 1.0 is the same as just using ONE.
> (you're still multiplying the src alpha by 1.0 with your change, not
> replacing the source alpha value with 1.0).

Oh, that is true, it is still just a multiplier.

> 
> Basically, I think your original patch is equivalent to this and bettter
> than this, and if we want to actually make the no-alpha-bits-present
> thing work, we need to override the bits in the surface state or in the
> generated code.  In the normal draw path, it's done for sampling by the
> swizzling code in brw_wm_surface_state.c, and the blending overrides is
> just to fix up the alpha blending stage which doesn't pay attention to
> that for the destination surface.
> 
> So, the original patch is:
> 
> Reviewed-by: Eric Anholt <eric at anholt.net>

Ok, thanks for the careful review!