[PATCH 5/5] user32: Select more appropriate stretch mode for colored images interpolation.

[Alexandre Julliard]

Paul Gofman <gofmanp at gmail.com> writes:

> My tests show that the full color images (24bpp) are downsampled using
> HALFTONE stretch mode, 1 bit images use BLACKONWHITE (as it works now
> in Wine), and anything between works like COLORONCOLOR mode. HALFTONE
> mode is not currently supported by gdi32 and falls back to
> COLORONCOLOR (STRECTH_DELETESCANS). This still makes more sense than
> using BLACKONWHITE for color images, but does not allow to fit the
> test for 24bpp bitmap. It could probably look more appropriate to set
> COLORONCOLOR mode for color images with less than 24bpp, but this way
> it won't fit any of my tests at all by now without changing gdi32
> stretch code. If STRECTH_DELETESCANS mode is used,
> stretch_bitmapinfo() in gdi32/dibdrv/bitblt.c takes a bit different
> (optimized) path and drops wrong scans (not those dropped on Windows
> or when HALFTONE mode is used). This difference should not matter much
> in practice in most cases though. I see the following possible ways:
>
> 1. Use a more appropriate stretch mode in CopyImage() / LoadImage()
> for color images regardless of gdi32 stuff. It will eliminate major
> image colors distortions currently introduced when ANDing color values
> during stretch.

We can certainly change this first, even if gdi32 doesn't do the right
thing yet.  But probably not during code freeze...

-- 
Alexandre Julliard
julliard at winehq.org