Re: [Pysdl-devel] Comparison of blit speed by file format

[Mark B. <mb...@0x...>]

On Thu, 20 Apr 2000, Eric Jacobs wrote:
> > 
> > Wow! Not only did that make the PNG and BMP times the same, it cut
> > them by about 40%! Very nice. Thanks for your help.
> 
> I second that wow! However, I'm having a little problem. Whenever I
> call either convert() or convert_display(), the alpha channel seems
> to be lost. This is coming off of PNGs. If I don't call the convert,
> the blit is much slower, but the alpha is preserved. Any ideas?

When you convert a surface to the format of the video surface, you're going to
lose your per-pixel alpha information. This is because the image is literally
converted to the format of the display image. So a 32-bit RGBA PNG is converted
to a 16-bit 5-5|6-5 video surface, or a 24-bit surface, or so on and so forth.

If you want to preserve the per-pixel alpha information, don't convert the
surface.