Re: [pygame] Pygame alpha blits and self blitting

[Lenard Lindstrom <len-l@xxxxxxxxx>]

I have refined overlapping blit detection so that SDL is used whenever 
possible. However, there is a slight difference between the SDL and 
Pygame blit blends. This means a blit to self differs from a blit to 
another surface with same format and image. The color differences are 
small, but noticeable when compared side-by-side. I have attached a 
small program that displays comparable colors from a Pygame and SDL blit 
using 16 bit surfaces. 32 bit surfaces give almost identical results. 
The  Pygame colors, on top, are lighter. Note the colors don't differ in 
all cases.

Lenard

Lenard Lindstrom wrote:
> True, but I have already done it the hard way. Now to thoroughly test.
>
> Lenard
>
>
> Brian Fisher wrote:
> > A simple shotgun fix to bad blitters when blitting a surface to 
> > itself could be blitting to itself from a copy.
> >
> > On Sat, Feb 14, 2009 at 5:10 PM, Lenard Lindstrom <len-l@xxxxxxxxx 
> > <mailto:len-l@xxxxxxxxx>> wrote:
> >
> >     The SDL blitters are used when the destination has no SRCALPHA and
> >     colorkey or a different pixel size from the source. As I mentioned
> >     earlier, it is tricky  identifying a problematic self blit. It is
> >     done by PygameSoftBlit in alphablit.c, but at that point Pygame
> >     has committed to doing the blit itself. Of course SDL_Blit could
> >     be called from PyGameSoftBlit or the address calculations --
> >     involving resolving Rect boundaries -- can be moved to
> >     PySurface_Blit in surface.c. For the moment I just want to get it
> >     working correctly. It can be tweaked later. Besides, if the SDL
> >     blit bugs are fixed, then this patch becomes unnecessary. A search
> >     in their Bugzille didn't show any bug reports on colorkey blit
> >     problems though. I only found a one bug report on a problems
> >     blitting one part of a large surface onto another part.
> >
> >     Lenard
> >
> >
> >
> >     René Dudfield wrote:
> >
> >         Hi,
> >
> >         I was seeing if it's possible to use the SDL color key
> >         blitters for
> >         the cases where they work?  Since they are all mostly
> >         optimized mmx...
> >         but maybe I'm missunderstanding what you've done.
> >
> >         nice work on all the blitter fix-ups by the way :)
> >
> >
> >         cheers!


--
Lenard Lindstrom
<len-l@xxxxxxxxx>

Attachment: colordif.py
Description: application/python