[Scummvm-devel] Overlay handling

[Max Horn]

Am 22.01.2009 um 05:35 schrieb Johannes Schickel:

> Max Horn schrieb:
>>>> And in fact, nothing uses the alpha channel anymore,
>>>>
>>> Huh?  So the DC is nothing then?
>>>
>>
>> Of course the DC port is not "nothing" -- sorry, didn't mean for it  
>> to
>> come across like that. Let me rephrase the two statements:
>>
>> (1) The DC port is currently the only port providing support for an
>> overlay with an alpha channel.
>>
>
> Not quite true AFAIK. The PSP backend has an 1bit alpha channel in its
> overlay, at least when I remember it correctly. I had some talk about
> that with joostp, when I was working on the old "new gui". Of course  
> one
> might want to argue whether to call it "alpha channel" or not :-).
> (Seeing that you're talking about 1bit alpha channels later on I guess
> you would call it "alpha channel")

It was meant in the sense of the following "definition":

		/**
		 * Set to true if the overlay pixel format has an alpha channel.
		 * This should only be set if it offers at least 3-4 bits of accuracy,
		 * as opposed to a single alpha bit.
		 */
		kFeatureOverlaySupportsAlpha,


In later parts of the email, I indeed used it in a more liberal  
meaning :). Anyway, now that we have an overlay PixelFormat, we don't  
need kFeatureOverlaySupportsAlpha anymore -- one can accurately  
determine from the overlay format whether an alpha channel exists and  
how many bits it has. Of course that wasn't possible until very  
recently (in particular it wasn't while the new GUI code was created).


Cheers,
Max