actions/itgmania212121
1
0
Fork 0
Code Issues Pull Requests Actions 1 Packages Projects Releases Wiki Activity

dither in integer space (faster)

Browse Source 
(started to write another resize filter and ended up doing this instead)
This commit is contained in:
Glenn Maynard
2002-10-30 06:03:38 +00:00
parent 7958f06c11
commit f49876b23e
1 changed files with 28 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files
stepmania/src/SDL_dither.cpp
+28 -11
View File
@@ -6,17 +6,20 @@
#define DitherMatDim 4
/* Scale these to [0..1): */
static const float DitherMatCalc[DitherMatDim][DitherMatDim] =
/* Fractions, 0/16 to 15/16: */
static const int DitherMat[DitherMatDim][DitherMatDim] =
{
0/16., 8/16., 2/16., 10/16.,
12/16., 4/16., 14/16., 6/16.,
3/16., 11/16., 1/16., 9/16.,
15/16., 7/16., 13/16., 5/16.
0, 8, 2, 10,
12, 4, 14, 6,
3, 11, 1, 9,
15, 7, 13, 5
};
static int DitherMatCalc[DitherMatDim][DitherMatDim];
static bool DitherMatCalc_initted = false;
/* conv is the ratio from the input to the output. */
static Uint8 DitherPixel(int x, int y, int intensity, float conv)
static Uint8 DitherPixel(int x, int y, int intensity, int conv)
{
/* The intensity matrix wraps. This assumes the matrix dims are a power of 2. */
x &= DitherMatDim-1;
@@ -33,17 +36,31 @@ static Uint8 DitherPixel(int x, int y, int intensity, float conv)
* the number is to the next value. */
/* Convert the number to the destination range. */
float out_intensity = intensity * conv;
int out_intensity = intensity * conv;
/* Add bias. */
out_intensity += DitherMatCalc[y][x];
/* Truncate, and add e to make sure a value of 14.999998 -> 15. */
return Uint8(out_intensity + 0.00001f);
return Uint8((out_intensity + 1) >> 16);
}
void SM_SDL_OrderedDither(const SDL_Surface *src, SDL_Surface *dst)
{
if(!DitherMatCalc_initted) {
for(int i = 0; i < DitherMatDim; ++i) {
for(int j = 0; j < DitherMatDim; ++j) {
/* Each value is 0..15. They represent 0/16 through 15/16.
* Set DitherMatCalc to that value * 65536, so we can do it
* with integer calcs. */
DitherMatCalc[i][j] = DitherMat[i][j] * 65536 / 16;
}
}
DitherMatCalc_initted = true;
}
/* We can't dither to paletted surfaces. */
ASSERT(dst->format->BytesPerPixel > 1);
@@ -52,12 +69,12 @@ void SM_SDL_OrderedDither(const SDL_Surface *src, SDL_Surface *dst)
mySDL_GetBitsPerChannel(dst->format, dst_cbits);
/* Calculate the ratio from the old bit depth to the new for each color channel. */
float conv[4];
int conv[4];
for(int i = 0; i < 4; ++i)
{
int MaxInputIntensity = (1 << src_cbits[i])-1;
int MaxOutputIntensity = (1 << dst_cbits[i])-1;
conv[i] = MaxOutputIntensity / float(MaxInputIntensity);
conv[i] = MaxOutputIntensity * 65536 / MaxInputIntensity;
}
/* For each row: */