[Scummvm-devel] 16bit alpha blending

[Johannes Schickel]

On 02/20/2011 01:16 PM, Marcus Comstedt wrote:
> This is probably a non-issue for the main game surface, because there
> is nothing to blend it against (I disable alpha blending for this
> surface in the DC backend), but for the cursor surface it could make
> a difference.
>

I agree that for the game surface we should just ignore the alpha bits.

> So should we take some kind of policy decision on which kind of alpha
> blending a pixelformat with alpha has, or allow the backend to provide
> multiple and let the engine choose?
>

I am not sure whether we should really allow more alpha blending on the 
cursor surface than either drawing a pixel (full alpha) or not drawing 
it (alpha is zero). That of course still requires some checking by the 
backend that the cursor surface data does not use alpha values in 
between. On the other hand IIRC even the 16bpp engines are using a 
colorkey for the cursor at the moment.

Since there is currently no engine (that I am aware of), which wants to 
take advantage of an alpha value on the cursor, it feels like over 
engineering if we would add support for multiple blending modes now.

// Johannes