Okay, I cleaned up the function with more general support for palettized
and non-palettized modes. I’m attaching the file so you can try it out.
Please let me know if this works. 
Thanks!
-Sam Lantinga, Software Engineer, Blizzard Entertainment
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/*
SDL - Simple DirectMedia Layer
Copyright © 1997-2004 Sam Lantinga
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the Free
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Sam Lantinga
@slouken
*/
#ifdef SAVE_RCSID
static char rcsid =
"@(#) $Id: SDL_pixels.c,v 1.13 2005/01/12 19:38:24 slouken Exp $";
#endif
/* General (mostly internal) pixel/color manipulation routines for SDL */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include “SDL_error.h”
#include “SDL_endian.h”
#include “SDL_video.h”
#include “SDL_sysvideo.h”
#include “SDL_blit.h”
#include “SDL_pixels_c.h”
#include “SDL_RLEaccel_c.h”
/* Helper functions /
/
-
Allocate a pixel format structure and fill it according to the given info.
*/
SDL_PixelFormat *SDL_AllocFormat(int bpp,
Uint32 Rmask, Uint32 Gmask, Uint32 Bmask, Uint32 Amask)
{
SDL_PixelFormat *format;
Uint32 mask;
/* Allocate an empty pixel format structure */
format = malloc(sizeof(*format));
if ( format == NULL ) {
SDL_OutOfMemory();
return(NULL);
}
memset(format, 0, sizeof(*format));
format->alpha = SDL_ALPHA_OPAQUE;
/* Set up the format /
format->BitsPerPixel = bpp;
format->BytesPerPixel = (bpp+7)/8;
if ( Rmask || Bmask || Gmask ) { / Packed pixels with custom mask /
format->palette = NULL;
format->Rshift = 0;
format->Rloss = 8;
if ( Rmask ) {
for ( mask = Rmask; !(mask&0x01); mask >>= 1 )
++format->Rshift;
for ( ; (mask&0x01); mask >>= 1 )
–format->Rloss;
}
format->Gshift = 0;
format->Gloss = 8;
if ( Gmask ) {
for ( mask = Gmask; !(mask&0x01); mask >>= 1 )
++format->Gshift;
for ( ; (mask&0x01); mask >>= 1 )
–format->Gloss;
}
format->Bshift = 0;
format->Bloss = 8;
if ( Bmask ) {
for ( mask = Bmask; !(mask&0x01); mask >>= 1 )
++format->Bshift;
for ( ; (mask&0x01); mask >>= 1 )
–format->Bloss;
}
format->Ashift = 0;
format->Aloss = 8;
if ( Amask ) {
for ( mask = Amask; !(mask&0x01); mask >>= 1 )
++format->Ashift;
for ( ; (mask&0x01); mask >>= 1 )
–format->Aloss;
}
format->Rmask = Rmask;
format->Gmask = Gmask;
format->Bmask = Bmask;
format->Amask = Amask;
} else if ( bpp > 8 ) { / Packed pixels with standard mask /
/ R-G-B /
if ( bpp > 24 )
bpp = 24;
format->Rloss = 8-(bpp/3);
format->Gloss = 8-(bpp/3)-(bpp%3);
format->Bloss = 8-(bpp/3);
format->Rshift = ((bpp/3)+(bpp%3))+(bpp/3);
format->Gshift = (bpp/3);
format->Bshift = 0;
format->Rmask = ((0xFF>>format->Rloss)<Rshift);
format->Gmask = ((0xFF>>format->Gloss)<Gshift);
format->Bmask = ((0xFF>>format->Bloss)<Bshift);
} else { / Palettized mode */
int i, ncolors = 1;
for ( i = 0; i < bpp; ++i ) {
ncolors *= 2;
}
format->palette = (SDL_Palette )malloc(sizeof(SDL_Palette));
if ( format->palette == NULL ) {
SDL_FreeFormat(format);
SDL_OutOfMemory();
return(NULL);
}
(format->palette)->ncolors = ncolors;
(format->palette)->colors = (SDL_Color )malloc(
(format->palette)->ncolorssizeof(SDL_Color));
if ( (format->palette)->colors == NULL ) {
SDL_FreeFormat(format);
SDL_OutOfMemory();
return(NULL);
}
if ( ncolors == 2 ) {
/ Create a black and white bitmap palette /
format->palette->colors[0].r = 0xFF;
format->palette->colors[0].g = 0xFF;
format->palette->colors[0].b = 0xFF;
format->palette->colors[1].r = 0x00;
format->palette->colors[1].g = 0x00;
format->palette->colors[1].b = 0x00;
} else {
/ Create an empty palette /
memset((format->palette)->colors, 0,
(format->palette)->ncolorssizeof(SDL_Color));
}
/* Palettized formats have no mask info */
format->Rloss = 8;
format->Gloss = 8;
format->Bloss = 8;
format->Aloss = 8;
format->Rshift = 0;
format->Gshift = 0;
format->Bshift = 0;
format->Ashift = 0;
format->Rmask = 0;
format->Gmask = 0;
format->Bmask = 0;
format->Amask = 0;
}
return(format);
}
SDL_PixelFormat *SDL_ReallocFormat(SDL_Surface *surface, int bpp,
Uint32 Rmask, Uint32 Gmask, Uint32 Bmask, Uint32 Amask)
{
if ( surface->format ) {
SDL_FreeFormat(surface->format);
SDL_FormatChanged(surface);
}
surface->format = SDL_AllocFormat(bpp, Rmask, Gmask, Bmask, Amask);
return surface->format;
}
/*
-
Change any previous mappings from/to the new surface format
*/
void SDL_FormatChanged(SDL_Surface surface)
{
static int format_version = 0;
++format_version;
if ( format_version < 0 ) { / It wrapped… /
format_version = 1;
}
surface->format_version = format_version;
SDL_InvalidateMap(surface->map);
}
/
-
Free a previously allocated format structure
*/
void SDL_FreeFormat(SDL_PixelFormat format)
{
if ( format ) {
if ( format->palette ) {
if ( format->palette->colors ) {
free(format->palette->colors);
}
free(format->palette);
}
free(format);
}
}
/
-
Calculate an 8-bit (3 red, 3 green, 2 blue) dithered palette of colors
*/
void SDL_DitherColors(SDL_Color colors, int bpp)
{
int i;
if(bpp != 8)
return; / only 8bpp supported right now */
for(i = 0; i < 256; i++) {
int r, g, b;
/* map each bit field to the full [0, 255] interval,
so 0 is mapped to (0, 0, 0) and 255 to (255, 255, 255) /
r = i & 0xe0;
r |= r >> 3 | r >> 6;
colors[i].r = r;
g = (i << 3) & 0xe0;
g |= g >> 3 | g >> 6;
colors[i].g = g;
b = i & 0x3;
b |= b << 2;
b |= b << 4;
colors[i].b = b;
}
}
/
-
Calculate the pad-aligned scanline width of a surface
*/
Uint16 SDL_CalculatePitch(SDL_Surface *surface)
{
Uint16 pitch;
/* Surface should be 4-byte aligned for speed /
pitch = surface->wsurface->format->BytesPerPixel;
switch (surface->format->BitsPerPixel) {
case 1:
pitch = (pitch+7)/8;
break;
case 4:
pitch = (pitch+1)/2;
break;
default:
break;
}
pitch = (pitch + 3) & ~3; /* 4-byte aligning /
return(pitch);
}
/
-
Match an RGB value to a particular palette index
*/
Uint8 SDL_FindColor(SDL_Palette pal, Uint8 r, Uint8 g, Uint8 b)
{
/ Do colorspace distance matching */
unsigned int smallest;
unsigned int distance;
int rd, gd, bd;
int i;
Uint8 pixel=0;
smallest = ~0;
for ( i=0; incolors; ++i ) {
rd = pal->colors[i].r - r;
gd = pal->colors[i].g - g;
bd = pal->colors[i].b - b;
distance = (rdrd)+(gdgd)+(bdbd);
if ( distance < smallest ) {
pixel = i;
if ( distance == 0 ) { / Perfect match! */
break;
}
smallest = distance;
}
}
return(pixel);
}
/* Find the opaque pixel value corresponding to an RGB triple */
Uint32 SDL_MapRGB(SDL_PixelFormat *format, Uint8 r, Uint8 g, Uint8 b)
{
if ( format->palette == NULL ) {
return (r >> format->Rloss) << format->Rshift
| (g >> format->Gloss) << format->Gshift
| (b >> format->Bloss) << format->Bshift
| format->Amask;
} else {
return SDL_FindColor(format->palette, r, g, b);
}
}
/* Find the pixel value corresponding to an RGBA quadruple */
Uint32 SDL_MapRGBA(SDL_PixelFormat *format, Uint8 r, Uint8 g, Uint8 b, Uint8 a)
{
if ( format->palette == NULL ) {
return (r >> format->Rloss) << format->Rshift
| (g >> format->Gloss) << format->Gshift
| (b >> format->Bloss) << format->Bshift
| ((a >> format->Aloss) << format->Ashift & format->Amask);
} else {
return SDL_FindColor(format->palette, r, g, b);
}
}
void SDL_GetRGBA(Uint32 pixel, SDL_PixelFormat *fmt,
Uint8 *r, Uint8 *g, Uint8 *b, Uint8 a)
{
if ( fmt->palette == NULL ) {
/
* This makes sure that the result is mapped to the
* interval [0…255], and the maximum value for each
* component is 255. This is important to make sure
* that white is indeed reported as (255, 255, 255),
* and that opaque alpha is 255.
* This only works for RGB bit fields at least 4 bit
* wide, which is almost always the case.
*/
unsigned v;
v = (pixel & fmt->Rmask) >> fmt->Rshift;
*r = (v << fmt->Rloss) + (v >> (8 - (fmt->Rloss << 1)));
v = (pixel & fmt->Gmask) >> fmt->Gshift;
*g = (v << fmt->Gloss) + (v >> (8 - (fmt->Gloss << 1)));
v = (pixel & fmt->Bmask) >> fmt->Bshift;
*b = (v << fmt->Bloss) + (v >> (8 - (fmt->Bloss << 1)));
if(fmt->Amask) {
v = (pixel & fmt->Amask) >> fmt->Ashift;
*a = (v << fmt->Aloss) + (v >> (8 - (fmt->Aloss << 1)));
} else {
*a = SDL_ALPHA_OPAQUE;
}
} else {
*r = fmt->palette->colors[pixel].r;
*g = fmt->palette->colors[pixel].g;
*b = fmt->palette->colors[pixel].b;
*a = SDL_ALPHA_OPAQUE;
}
}
void SDL_GetRGB(Uint32 pixel, SDL_PixelFormat *fmt, Uint8 *r,Uint8 *g,Uint8 b)
{
if ( fmt->palette == NULL ) {
/ the note for SDL_GetRGBA above applies here too */
unsigned v;
v = (pixel & fmt->Rmask) >> fmt->Rshift;
*r = (v << fmt->Rloss) + (v >> (8 - (fmt->Rloss << 1)));
v = (pixel & fmt->Gmask) >> fmt->Gshift;
*g = (v << fmt->Gloss) + (v >> (8 - (fmt->Gloss << 1)));
v = (pixel & fmt->Bmask) >> fmt->Bshift;
*b = (v << fmt->Bloss) + (v >> (8 - (fmt->Bloss << 1)));
} else {
*r = fmt->palette->colors[pixel].r;
*g = fmt->palette->colors[pixel].g;
*b = fmt->palette->colors[pixel].b;
}
}
/* Apply gamma to a set of colors - this is easy. */
void SDL_ApplyGamma(Uint16 *gamma, SDL_Color *colors, SDL_Color *output,
int ncolors)
{
int i;
for ( i=0; i<ncolors; ++i ) {
output[i].r = gamma[0*256 + colors[i].r] >> 8;
output[i].g = gamma[1*256 + colors[i].g] >> 8;
output[i].b = gamma[2*256 + colors[i].b] >> 8;
}
}
/* Map from Palette to Palette */
static Uint8 *Map1to1(SDL_Palette *src, SDL_Palette *dst, int *identical)
{
Uint8 *map;
int i;
if ( identical ) {
if ( src->ncolors <= dst->ncolors ) {
/* If an identical palette, no need to map */
if ( memcmp(src->colors, dst->colors, src->ncolors*
sizeof(SDL_Color)) == 0 ) {
*identical = 1;
return(NULL);
}
}
*identical = 0;
}
map = (Uint8 *)malloc(src->ncolors);
if ( map == NULL ) {
SDL_OutOfMemory();
return(NULL);
}
for ( i=0; i<src->ncolors; ++i ) {
map[i] = SDL_FindColor(dst,
src->colors[i].r, src->colors[i].g, src->colors[i].b);
}
return(map);
}
/* Map from Palette to BitField */
static Uint8 *Map1toN(SDL_Palette *src, SDL_PixelFormat *dst)
{
Uint8 *map;
int i;
int bpp;
unsigned alpha;
bpp = ((dst->BytesPerPixel == 3) ? 4 : dst->BytesPerPixel);
map = (Uint8 *)malloc(src->ncolors*bpp);
if ( map == NULL ) {
SDL_OutOfMemory();
return(NULL);
}
alpha = dst->Amask ? SDL_ALPHA_OPAQUE : 0;
/* We memory copy to the pixel map so the endianness is preserved */
for ( i=0; i<src->ncolors; ++i ) {
ASSEMBLE_RGBA(&map[i*bpp], dst->BytesPerPixel, dst,
src->colors[i].r, src->colors[i].g,
src->colors[i].b, alpha);
}
return(map);
}
/* Map from BitField to Dithered-Palette to Palette */
static Uint8 *MapNto1(SDL_PixelFormat *src, SDL_Palette *dst, int identical)
{
/ Generate a 256 color dither palette */
SDL_Palette dithered;
SDL_Color colors[256];
/* SDL_DitherColors does not initialize the 'unused' component of colors,
but Map1to1 compares it against dst, so we should initialize it. */
memset(colors, 0, sizeof(colors));
dithered.ncolors = 256;
SDL_DitherColors(colors, 8);
dithered.colors = colors;
return(Map1to1(&dithered, dst, identical));
}
SDL_BlitMap *SDL_AllocBlitMap(void)
{
SDL_BlitMap *map;
/* Allocate the empty map */
map = (SDL_BlitMap *)malloc(sizeof(*map));
if ( map == NULL ) {
SDL_OutOfMemory();
return(NULL);
}
memset(map, 0, sizeof(*map));
/* Allocate the software blit data */
map->sw_data = (struct private_swaccel *)malloc(sizeof(*map->sw_data));
if ( map->sw_data == NULL ) {
SDL_FreeBlitMap(map);
SDL_OutOfMemory();
return(NULL);
}
memset(map->sw_data, 0, sizeof(*map->sw_data));
/* It's ready to go */
return(map);
}
void SDL_InvalidateMap(SDL_BlitMap *map)
{
if ( ! map ) {
return;
}
map->dst = NULL;
map->format_version = (unsigned int)-1;
if ( map->table ) {
free(map->table);
map->table = NULL;
}
}
int SDL_MapSurface (SDL_Surface *src, SDL_Surface *dst)
{
SDL_PixelFormat *srcfmt;
SDL_PixelFormat *dstfmt;
SDL_BlitMap *map;
/* Clear out any previous mapping */
map = src->map;
if ( (src->flags & SDL_RLEACCEL) == SDL_RLEACCEL ) {
SDL_UnRLESurface(src, 1);
}
SDL_InvalidateMap(map);
/* Figure out what kind of mapping we're doing */
map->identity = 0;
srcfmt = src->format;
dstfmt = dst->format;
switch (srcfmt->BytesPerPixel) {
case 1:
switch (dstfmt->BytesPerPixel) {
case 1:
/* Palette --> Palette */
/* If both SDL_HWSURFACE, assume have same palette */
if ( ((src->flags & SDL_HWSURFACE) == SDL_HWSURFACE) &&
((dst->flags & SDL_HWSURFACE) == SDL_HWSURFACE) ) {
map->identity = 1;
} else {
map->table = Map1to1(srcfmt->palette,
dstfmt->palette, &map->identity);
}
if ( ! map->identity ) {
if ( map->table == NULL ) {
return(-1);
}
}
if (srcfmt->BitsPerPixel!=dstfmt->BitsPerPixel)
map->identity = 0;
break;
default:
/* Palette --> BitField */
map->table = Map1toN(srcfmt->palette, dstfmt);
if ( map->table == NULL ) {
return(-1);
}
break;
}
break;
default:
switch (dstfmt->BytesPerPixel) {
case 1:
/* BitField --> Palette */
map->table = MapNto1(srcfmt,
dstfmt->palette, &map->identity);
if ( ! map->identity ) {
if ( map->table == NULL ) {
return(-1);
}
}
map->identity = 0; /* Don't optimize to copy */
break;
default:
/* BitField --> BitField */
if ( FORMAT_EQUAL(srcfmt, dstfmt) )
map->identity = 1;
break;
}
break;
}
map->dst = dst;
map->format_version = dst->format_version;
/* Choose your blitters wisely */
return(SDL_CalculateBlit(src));
}
void SDL_FreeBlitMap(SDL_BlitMap *map)
{
if ( map ) {
SDL_InvalidateMap(map);
if ( map->sw_data != NULL ) {
free(map->sw_data);
}
free(map);
}
}