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optimize SM_SDL_ErrorDiffusionDither: takes about half as long now

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(but it still takes 3x as long as SM_SDL_OrderedDither, and I still
see banding in both vertical and horizontal gradients ...)
This commit is contained in:
Glenn Maynard
2004-04-10 23:09:41 +00:00
parent 668be17204
commit fd839eb946
1 changed files with 24 additions and 1 deletions
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stepmania/src/SDL_dither.cpp
+24 -1
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@@ -1,5 +1,6 @@
#include "global.h"
#include "RageUtil.h"
#include "SDL.h"
#include "SDL_dither.h"
#include "SDL_utils.h"
@@ -139,6 +140,26 @@ void SM_SDL_OrderedDither(const SDL_Surface *src, SDL_Surface *dst)
#define CLAMP(x, l, h) {if (x > h) x = h; else if (x < l) x = l;}
/* Return "random" numbers in [0,2]; this is for SM_SDL_ErrorDiffusionDither (rand() is too slow). */
static inline int GetFastRand()
{
static int RandomNumbers[] =
{
2, 1, 0, 2, 0, 2, 2, 1, 0, 1, 1, 2, 2, 0, 1, 1, 2, 2, 1, 0, 1, 0, 1, 2, 1, 0, 2, 1, 0, 1, 1, 0,
2, 1, 1, 2, 1, 0, 0, 1, 1, 2, 0, 2, 0, 1, 0, 1, 2, 0, 0, 1, 1, 2, 0, 2, 1, 2, 2, 2, 2, 1, 1, 1,
1, 0, 2, 1, 2, 1, 1, 1, 2, 1, 0, 0, 1, 0, 0, 2, 0, 1, 0, 1, 2, 2, 0, 0, 0, 2, 2, 1, 2, 2, 2, 2,
1, 2, 1, 0, 2, 0, 1, 0, 2, 1, 2, 1, 1, 0, 1, 1, 2, 0, 0, 2, 2, 2, 1, 0, 0, 1, 2, 1, 2, 0, 0, 2,
2, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 2, 2, 2, 0, 0, 0, 1, 2, 0, 1, 1, 0, 0, 0, 2, 1, 2, 0, 0, 1,
1, 2, 0, 1, 1, 2, 2, 1, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1, 2, 0, 0, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 2,
0, 1, 2, 0, 2, 2, 0, 2, 1, 0, 0, 2, 2, 2, 2, 2, 2, 1, 1, 2, 2, 2, 0, 1, 0, 1, 2, 1, 2, 1, 0, 0,
1, 0, 0, 0, 2, 2, 2, 2, 1, 2, 1, 0, 0, 2, 1, 0, 1, 2, 0, 2, 2, 0, 0, 0, 2, 2, 0, 0, 2, 0, 1, 1
};
static int iNextNumber = 0;
if( iNextNumber == ARRAYSIZE(RandomNumbers) )
iNextNumber = 0;
return RandomNumbers[ iNextNumber++ ];
}
void SM_SDL_ErrorDiffusionDither(const SDL_Surface *src, SDL_Surface *dst)
{
/* We can't dither to paletted surfaces. */
@@ -194,7 +215,9 @@ void SM_SDL_ErrorDiffusionDither(const SDL_Surface *src, SDL_Surface *dst)
CLAMP( accumError[c], -128, +128 );
// Keep only a fraction of the error to make the effect more subtle.
accumError[c] /= (rand()%4)+1;
// This used to divide by [1,4]; shift right by [0,2] to get a similar
// (but much faster) effect.
accumError[c] >>= (GetFastRand())+1;
}
srcp += src->format->BytesPerPixel;