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when dithering, round the alpha channel instead of truncating

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Glenn Maynard
2004-05-02 03:41:33 +00:00
parent 58d63cb476
commit ac81016af4
1 changed files with 14 additions and 2 deletions
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stepmania/src/SDL_dither.cpp
+14 -2
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@@ -125,7 +125,13 @@ void SM_SDL_OrderedDither(const SDL_Surface *src, SDL_Surface *dst)
int out_intensity = colors[3] * conv[3];
/* Truncate, and add e to make sure a value of 14.999998 -> 15. */
colors[3] = Uint8((out_intensity + 1) >> 16);
// colors[3] = Uint8((out_intensity + 1) >> 16);
/* I don't remember why this used to truncate. Doing that causes
* dithering to an image with 1-bit alpha to be transparent on all
* source alpha values except for full-opaque, which is wrong.
* Add .5, so we round. */
colors[3] = Uint8((out_intensity + 32767) >> 16);
}
/* Raw value -> int -> pixel */
@@ -249,7 +255,13 @@ void SM_SDL_ErrorDiffusionDither(const SDL_Surface *src, SDL_Surface *dst)
int out_intensity = colors[3] * conv[3];
/* Truncate, and add e to make sure a value of 14.999998 -> 15. */
colors[3] = Uint8((out_intensity + 1) >> 16);
// colors[3] = Uint8((out_intensity + 1) >> 16);
/* I don't remember why this used to truncate. Doing that causes
* dithering to an image with 1-bit alpha to be transparent on all
* source alpha values except for full-opaque, which is wrong.
* Add .5, so we round. */
colors[3] = Uint8((out_intensity + 32767) >> 16);
}
mySDL_SetRawRGBAV( dstp, dst, colors );