/*         ______   ___    ___ 
 *        /\  _  \ /\_ \  /\_ \ 
 *        \ \ \L\ \\//\ \ \//\ \      __     __   _ __   ___ 
 *         \ \  __ \ \ \ \  \ \ \   /'__`\ /'_ `\/\`'__\/ __`\
 *          \ \ \/\ \ \_\ \_ \_\ \_/\  __//\ \L\ \ \ \//\ \L\ \
 *           \ \_\ \_\/\____\/\____\ \____\ \____ \ \_\\ \____/
 *            \/_/\/_/\/____/\/____/\/____/\/___L\ \/_/ \/___/
 *                                           /\____/
 *                                           \_/__/
 *
 *      Blitting functions.
 *
 *      By Shawn Hargreaves.
 *
 *      Dithering code by James Hyman.
 *
 *      Transparency preserving code by Elias Pschernig.
 *
 *      See readme.txt for copyright information.
 */


#include <string.h>
#include "allegro.h"
#include "allegro/internal/aintern.h"



/* get_replacement_mask_color:
 *  Helper function to get a replacement color for the bitmap's mask color.
 */
static int get_replacement_mask_color(BITMAP *bmp)
{
   int depth, c, g = 0;

   depth = bitmap_color_depth(bmp);

   if (depth == 8) {
      if (rgb_map)
         return rgb_map->data[31][1][31];
      else
         return bestfit_color(_current_palette, 63, 1, 63);
   }
   else {
      do
         c = makecol_depth(depth, 255, ++g, 255);
      while (c == bitmap_mask_color(bmp));

      return c;
   }
}



/* blit_from_256:
 *  Expands 256 color images onto a truecolor destination.
 */
static void blit_from_256(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   #ifdef ALLEGRO_COLOR8

   int *dest_palette_color;
   uintptr_t s, d;
   unsigned char *ss;
   int x, y, c, rc;

   /* lookup table avoids repeated color format conversions */
   if (_color_conv & COLORCONV_KEEP_TRANS) {
      dest_palette_color = _AL_MALLOC_ATOMIC(256*sizeof(int));
      memcpy(dest_palette_color, _palette_expansion_table(bitmap_color_depth(dest)), 256*sizeof(int));

      rc = get_replacement_mask_color(dest);

      dest_palette_color[MASK_COLOR_8] = bitmap_mask_color(dest);

      for (c=0; c<256; c++) {
         if ((c != MASK_COLOR_8) &&
             (dest_palette_color[c] == bitmap_mask_color(dest)))
            dest_palette_color[c] = rc;
      }
   }
   else
      dest_palette_color = _palette_expansion_table(bitmap_color_depth(dest));

   /* worker macro */
   #define EXPAND_BLIT(bits, dsize)                                          \
   {                                                                         \
      if (is_memory_bitmap(src)) {                                           \
         /* fast version when reading from memory bitmap */                  \
         bmp_select(dest);                                                   \
                                                                             \
         for (y=0; y<h; y++) {                                               \
            ss = src->line[s_y+y] + s_x;                                     \
            d = bmp_write_line(dest, d_y+y) + d_x*dsize;                     \
                                                                             \
            for (x=0; x<w; x++) {                                            \
               bmp_write##bits(d, dest_palette_color[*ss]);                  \
               ss++;                                                         \
               d += dsize;                                                   \
            }                                                                \
         }                                                                   \
                                                                             \
         bmp_unwrite_line(dest);                                             \
      }                                                                      \
      else {                                                                 \
         /* slower version when reading from the screen */                   \
         for (y=0; y<h; y++) {                                               \
            s = bmp_read_line(src, s_y+y) + s_x;                             \
            d = bmp_write_line(dest, d_y+y) + d_x*dsize;                     \
                                                                             \
            for (x=0; x<w; x++) {                                            \
               bmp_select(src);                                              \
               c = bmp_read8(s);                                             \
                                                                             \
               bmp_select(dest);                                             \
               bmp_write##bits(d, dest_palette_color[c]);                    \
                                                                             \
               s++;                                                          \
               d += dsize;                                                   \
            }                                                                \
         }                                                                   \
                                                                             \
         bmp_unwrite_line(src);                                              \
         bmp_unwrite_line(dest);                                             \
      }                                                                      \
   }

   /* expand the above macro for each possible output depth */
   switch (bitmap_color_depth(dest)) {

      #ifdef ALLEGRO_COLOR16
      case 15:
      case 16:
         EXPAND_BLIT(16, sizeof(int16_t));
         break;
      #endif

      #ifdef ALLEGRO_COLOR24
      case 24:
         EXPAND_BLIT(24, 3);
         break;
      #endif

      #ifdef ALLEGRO_COLOR32
      case 32:
         EXPAND_BLIT(32, sizeof(int32_t));
         break;
      #endif
   }

   if (_color_conv & COLORCONV_KEEP_TRANS)
      _AL_FREE(dest_palette_color);

   #endif
}



/* worker macro for converting between two color formats, possibly with dithering */
#define CONVERT_BLIT_EX(sbits, ssize, dbits, dsize, MAKECOL)                 \
{                                                                            \
   if (_color_conv & COLORCONV_KEEP_TRANS) {                                 \
      int rc = get_replacement_mask_color(dest);                             \
      int src_mask = bitmap_mask_color(src);                                 \
      int dest_mask = bitmap_mask_color(dest);                               \
                                                                             \
      for (y=0; y<h; y++) {                                                  \
	 s = bmp_read_line(src, s_y+y) + s_x*ssize;                          \
	 d = bmp_write_line(dest, d_y+y) + d_x*dsize;                        \
                                                                             \
         for (x=0; x<w; x++) {                                               \
            bmp_select(src);                                                 \
            c = bmp_read##sbits(s);                                          \
                                                                             \
            if (c == src_mask)                                               \
               c = dest_mask;                                                \
            else {                                                           \
	       r = getr##sbits(c);                                           \
	       g = getg##sbits(c);                                           \
	       b = getb##sbits(c);                                           \
               c = MAKECOL;                                                  \
               if (c == dest_mask)                                           \
		 c = rc;			\
            }                                                                \
                                                                             \
            bmp_select(dest);                                                \
            bmp_write##dbits(d, c);                                          \
                                                                             \
            s += ssize;                                                      \
            d += dsize;                                                      \
         }                                                                   \
      }                                                                      \
   }                                                                         \
   else {                                                                    \
      for (y=0; y<h; y++) {                                                  \
	 s = bmp_read_line(src, s_y+y) + s_x*ssize;                          \
	 d = bmp_write_line(dest, d_y+y) + d_x*dsize;                        \
                                                                             \
         for (x=0; x<w; x++) {                                               \
            bmp_select(src);                                                 \
            c = bmp_read##sbits(s);                                          \
                                                                             \
            r = getr##sbits(c);                                              \
            g = getg##sbits(c);                                              \
            b = getb##sbits(c);                                              \
                                                                             \
            bmp_select(dest);                                                \
            bmp_write##dbits(d, MAKECOL);                                    \
                                                                             \
            s += ssize;                                                      \
            d += dsize;                                                      \
         }                                                                   \
      }                                                                      \
   }                                                                         \
                                                                             \
   bmp_unwrite_line(src);                                                    \
   bmp_unwrite_line(dest);                                                   \
}

#define CONVERT_BLIT(sbits, ssize, dbits, dsize) \
   CONVERT_BLIT_EX(sbits, ssize, dbits, dsize, makecol##dbits(r, g, b))
#define CONVERT_DITHER_BLIT(sbits, ssize, dbits, dsize) \
   CONVERT_BLIT_EX(sbits, ssize, dbits, dsize, \
                   makecol##dbits##_dither(r, g, b, x, y))



#if (defined ALLEGRO_COLOR8) || (defined GFX_HAS_VGA)

/* dither_blit:
 *  Blits with Floyd-Steinberg error diffusion.
 */
static void dither_blit(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   int prev_drawmode = _drawing_mode;
   int *errline[3];
   int *errnextline[3];
   int errpixel[3];
   int v[3], e[3], n[3];
   int x, y, i;
   int c, nc, rc;

   /* allocate memory for the error buffers */
   for (i=0; i<3; i++) {
      errline[i] = _AL_MALLOC_ATOMIC(sizeof(int) * w);
      errnextline[i] = _AL_MALLOC_ATOMIC(sizeof(int) * w);
   }

   /* free the buffers if there was an error allocating one */
   for (i=0; i<3; i++) {
      if ((!errline[i]) || (!errnextline[i]))
      goto getout;
   }

   /* initialize the error buffers */
   for (i=0; i<3; i++) {
      memset(errline[i], 0, sizeof(int) * w);
      memset(errnextline[i], 0, sizeof(int) * w);
      errpixel[i] = 0;
   }

   /* get the replacement color */
   rc = get_replacement_mask_color(dest);

   _drawing_mode = DRAW_MODE_SOLID;

   /* dither!!! */
   for (y =0; y<h; y++) {
      for (x =0; x<w; x++) {
         /* get the colour from the source bitmap */
         c = getpixel(src, s_x+x, s_y+y);
         v[0] = getr_depth(bitmap_color_depth(src), c);
         v[1] = getg_depth(bitmap_color_depth(src), c);
         v[2] = getb_depth(bitmap_color_depth(src), c);

         /* add the error from previous pixels */
         for (i=0; i<3; i++) {
            n[i] = v[i] + errline[i][x] + errpixel[i];

            if (n[i] > 255)
               n[i] = 255;

            if (n[i] < 0)
               n[i] = 0;
         }

         /* find the nearest matching colour */
         nc = makecol8(n[0], n[1], n[2]);
         if (_color_conv & COLORCONV_KEEP_TRANS) {
            if (c == bitmap_mask_color(src))
               putpixel(dest, d_x+x, d_y+y, bitmap_mask_color(dest));
            else if (nc == bitmap_mask_color(dest))
               putpixel(dest, d_x+x, d_y+y, rc);
            else
               putpixel(dest, d_x+x, d_y+y, nc);
         }
         else {
            putpixel(dest, d_x+x, d_y+y, nc);
         }
         v[0] = getr8(nc);
         v[1] = getg8(nc);
         v[2] = getb8(nc);

         /* calculate the error and store it */
         for (i=0; i<3; i++) {
            e[i] = n[i] - v[i];
            errpixel[i] = (int)((e[i] * 3)/8);
            errnextline[i][x] += errpixel[i];

            if (x != w-1)
               errnextline[i][x+1] = (int)(e[i]/4);
         }
      }

      /* update error buffers */
      for (i=0; i<3; i++) {
         memcpy(errline[i], errnextline[i], sizeof(int) * w);
         memset(errnextline[i], 0, sizeof(int) * w);
      }
   }

   _drawing_mode = prev_drawmode;

 getout:

   for (i=0; i<3; i++) {
      if (errline[i])
         _AL_FREE(errline[i]);

      if (errnextline[i])
         _AL_FREE(errnextline[i]);
   }
}

#endif



/* blit_from_15:
 *  Converts 15 bpp images onto some other destination format.
 */
static void blit_from_15(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   #ifdef ALLEGRO_COLOR16

   int x, y, c, r, g, b;
   uintptr_t s, d;

   switch (bitmap_color_depth(dest)) {

      #ifdef ALLEGRO_COLOR8
      case 8:
         if (_color_conv & COLORCONV_DITHER_PAL)
            dither_blit(src, dest, s_x, s_y, d_x, d_y, w, h);
         else 
            CONVERT_BLIT(15, sizeof(int16_t), 8, 1)
         break;
      #endif

      case 16:
         CONVERT_BLIT(15, sizeof(int16_t), 16, sizeof(int16_t))
         break;

      #ifdef ALLEGRO_COLOR24
      case 24:
         CONVERT_BLIT(15, sizeof(int16_t), 24, 3)
         break;
      #endif

      #ifdef ALLEGRO_COLOR32
      case 32:
         CONVERT_BLIT(15, sizeof(int16_t), 32, sizeof(int32_t))
         break;
      #endif
   }

   #endif
}



/* blit_from_16:
 *  Converts 16 bpp images onto some other destination format.
 */
static void blit_from_16(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   #ifdef ALLEGRO_COLOR16

   int x, y, c, r, g, b;
   uintptr_t s, d;

   switch (bitmap_color_depth(dest)) {

      #ifdef ALLEGRO_COLOR8
      case 8:
         if (_color_conv & COLORCONV_DITHER_PAL)
            dither_blit(src, dest, s_x, s_y, d_x, d_y, w, h);
         else 
            CONVERT_BLIT(16, sizeof(int16_t), 8, 1)
         break;
      #endif

      case 15:
         CONVERT_BLIT(16, sizeof(int16_t), 15, sizeof(int16_t))
         break;

      #ifdef ALLEGRO_COLOR24
      case 24:
         CONVERT_BLIT(16, sizeof(int16_t), 24, 3)
         break;
      #endif

      #ifdef ALLEGRO_COLOR32
      case 32:
         CONVERT_BLIT(16, sizeof(int16_t), 32, sizeof(int32_t))
         break;
      #endif
   }

   #endif 
}



/* blit_from_24:
 *  Converts 24 bpp images onto some other destination format.
 */
static void blit_from_24(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   #ifdef ALLEGRO_COLOR24

   int x, y, c, r, g, b;
   uintptr_t s, d;

   switch (bitmap_color_depth(dest)) {

      #ifdef ALLEGRO_COLOR8
      case 8:
         if (_color_conv & COLORCONV_DITHER_PAL)
            dither_blit(src, dest, s_x, s_y, d_x, d_y, w, h);
         else 
            CONVERT_BLIT(24, 3, 8, 1);
         break;
      #endif

      #ifdef ALLEGRO_COLOR16
      case 15:
         if (_color_conv & COLORCONV_DITHER_HI)
            CONVERT_DITHER_BLIT(24, 3, 15, sizeof(int16_t))
         else
            CONVERT_BLIT(24, 3, 15, sizeof(int16_t))
         break;

      case 16:
         if (_color_conv & COLORCONV_DITHER_HI)
            CONVERT_DITHER_BLIT(24, 3, 16, sizeof(int16_t))
         else
            CONVERT_BLIT(24, 3, 16, sizeof(int16_t))
         break;
      #endif

      #ifdef ALLEGRO_COLOR32
      case 32:
         CONVERT_BLIT(24, 3, 32, sizeof(int32_t))
         break;
      #endif
   }

   #endif 
}



/* blit_from_32:
 *  Converts 32 bpp images onto some other destination format.
 */
static void blit_from_32(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   #ifdef ALLEGRO_COLOR32

   int x, y, c, r, g, b;
   uintptr_t s, d;

   switch (bitmap_color_depth(dest)) {

      #ifdef ALLEGRO_COLOR8
      case 8:
         if (_color_conv & COLORCONV_DITHER_PAL)
            dither_blit(src, dest, s_x, s_y, d_x, d_y, w, h);
         else 
            CONVERT_BLIT(32, sizeof(int32_t), 8, 1)
         break;
      #endif

      #ifdef ALLEGRO_COLOR16
      case 15:
         if (_color_conv & COLORCONV_DITHER_HI)
            CONVERT_DITHER_BLIT(32, sizeof(int32_t), 15, sizeof(int16_t))
         else
            CONVERT_BLIT(32, sizeof(int32_t), 15, sizeof(int16_t))
         break;

      case 16:
         if (_color_conv & COLORCONV_DITHER_HI)
            CONVERT_DITHER_BLIT(32, sizeof(int32_t), 16, sizeof(int16_t))
         else
            CONVERT_BLIT(32, sizeof(int32_t), 16, sizeof(int16_t))
         break;
      #endif

      #ifdef ALLEGRO_COLOR24
      case 24:
         CONVERT_BLIT(32, sizeof(int32_t), 24, 3)
         break;
      #endif
   }

   #endif 
}



/* blit_to_or_from_modex:
 *  Converts between truecolor and planar mode-X bitmaps. This function is 
 *  painfully slow, but I don't think it is something that people will need
 *  to do very often...
 */
static void blit_to_or_from_modex(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   #ifdef GFX_HAS_VGA

   int x, y, c, r, g, b;
   int src_depth = bitmap_color_depth(src);
   int dest_depth = bitmap_color_depth(dest);

   int prev_drawmode = _drawing_mode;
   _drawing_mode = DRAW_MODE_SOLID;

   if ((src_depth != 8) && (_color_conv & COLORCONV_DITHER_PAL))
      dither_blit(src, dest, s_x, s_y, d_x, d_y, w, h);
   else {
      for (y=0; y<h; y++) {
         for (x=0; x<w; x++) {
            c = getpixel(src, s_x+x, s_y+y);
            r = getr_depth(src_depth, c);
            g = getg_depth(src_depth, c);
            b = getb_depth(src_depth, c);
            c = makecol_depth(dest_depth, r, g, b);
            putpixel(dest, d_x+x, d_y+y, c);
         }
      }
   }

   _drawing_mode = prev_drawmode;

   #endif
}



/* blit_between_formats:
 *  Blits an (already clipped) region between two bitmaps of different
 *  color depths, doing the appopriate format conversions.
 */
void _blit_between_formats(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   if ((is_planar_bitmap(src)) || (is_planar_bitmap(dest))) {
      blit_to_or_from_modex(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else {
      switch (bitmap_color_depth(src)) {

	 case 8:
	    blit_from_256(src, dest, s_x, s_y, d_x, d_y, w, h);
	    break;

	 case 15:
	    blit_from_15(src, dest, s_x, s_y, d_x, d_y, w, h);
	    break;

	 case 16:
	    blit_from_16(src, dest, s_x, s_y, d_x, d_y, w, h);
	    break;

	 case 24:
	    blit_from_24(src, dest, s_x, s_y, d_x, d_y, w, h);
	    break;

	 case 32:
	    blit_from_32(src, dest, s_x, s_y, d_x, d_y, w, h);
	    break;
      }
   }
}



/* blit_to_self:
 *  Blits an (already clipped) region between two areas of the same bitmap,
 *  checking which way around to do the blit.
 */
static void blit_to_self(BITMAP *src, BITMAP *dest, int s_x, int s_y, int d_x, int d_y, int w, int h)
{
   unsigned long sx, sy, dx, dy;
   BITMAP *tmp;

   if (dest->id & BMP_ID_NOBLIT) {
      /* with single-banked cards we have to use a temporary bitmap */
      tmp = create_bitmap(w, h);
      if (tmp) {
         src->vtable->blit_to_memory(src, tmp, s_x, s_y, 0, 0, w, h);
         dest->vtable->blit_from_memory(tmp, dest, 0, 0, d_x, d_y, w, h);
         destroy_bitmap(tmp);
      }
   }
   else {
      /* check which way round to do the blit */
      sx = s_x + src->x_ofs;
      sy = s_y + src->y_ofs;

      dx = d_x + dest->x_ofs;
      dy = d_y + dest->y_ofs;

      if ((sx+w <= dx) || (dx+w <= sx) || (sy+h <= dy) || (dy+h <= sy))
         dest->vtable->blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
      else if ((sy > dy) || ((sy == dy) && (sx > dx)))
         dest->vtable->blit_to_self_forward(src, dest, s_x, s_y, d_x, d_y, w, h);
      else if ((sx != dx) || (sy != dy))
         dest->vtable->blit_to_self_backward(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
}



/* helper for clipping a blit rectangle */
#define BLIT_CLIP()                                                          \
   /* check for ridiculous cases */                                          \
   if ((s_x >= src->w) || (s_y >= src->h) ||                                 \
       (d_x >= dest->cr) || (d_y >= dest->cb))                               \
      return;                                                                \
                                                                             \
   /* clip src left */                                                       \
   if (s_x < 0) {                                                            \
      w += s_x;                                                              \
      d_x -= s_x;                                                            \
      s_x = 0;                                                               \
   }                                                                         \
                                                                             \
   /* clip src top */                                                        \
   if (s_y < 0) {                                                            \
      h += s_y;                                                              \
      d_y -= s_y;                                                            \
      s_y = 0;                                                               \
   }                                                                         \
                                                                             \
   /* clip src right */                                                      \
   if (s_x+w > src->w)                                                       \
      w = src->w - s_x;                                                      \
                                                                             \
   /* clip src bottom */                                                     \
   if (s_y+h > src->h)                                                       \
      h = src->h - s_y;                                                      \
                                                                             \
   /* clip dest left */                                                      \
   if (d_x < dest->cl) {                                                     \
      d_x -= dest->cl;                                                       \
      w += d_x;                                                              \
      s_x -= d_x;                                                            \
      d_x = dest->cl;                                                        \
   }                                                                         \
                                                                             \
   /* clip dest top */                                                       \
   if (d_y < dest->ct) {                                                     \
      d_y -= dest->ct;                                                       \
      h += d_y;                                                              \
      s_y -= d_y;                                                            \
      d_y = dest->ct;                                                        \
   }                                                                         \
                                                                             \
   /* clip dest right */                                                     \
   if (d_x+w > dest->cr)                                                     \
      w = dest->cr - d_x;                                                    \
                                                                             \
   /* clip dest bottom */                                                    \
   if (d_y+h > dest->cb)                                                     \
      h = dest->cb - d_y;                                                    \
                                                                             \
   /* bottle out if zero size */                                             \
   if ((w <= 0) || (h <= 0))                                                 \
      return;



/* al_blit:
 * Copies a rectangular area of the source bitmap to the destination bitmap.
 * The dest_x and dest_y are the coordinates of the top-left corner in the
 * destination bitmap where the source bitmap will be drawn.
 */
void al_blit(int method, BITMAP *src, BITMAP *dest, int d_x, int d_y)
{
   int w, h;
   int s_x = 0, s_y = 0;
   ASSERT(src);
   ASSERT(dest);

   /* If method!=0, then bitmaps must be of the same colour depth */
   ASSERT(method !=0 || src->vtable->color_depth == dest->vtable->color_depth);
   
   w = src->w;
   h = src->h;
   BLIT_CLIP();
   

   
   /* Masked blit */
   if (method == AL_MASK_SOURCE) {
      dest->vtable->masked_blit(src, dest, s_x, s_y, d_x, d_y, w, h);
      return;
   }

   if (src->vtable->color_depth != dest->vtable->color_depth) {
      /* need to do a color conversion */
      dest->vtable->blit_between_formats(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else if (is_same_bitmap(src, dest)) {
      /* special handling for overlapping regions */
      blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else if (is_video_bitmap(dest)) {
      /* drawing onto video bitmaps */
      if (is_video_bitmap(src))
         dest->vtable->blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
      else if (is_system_bitmap(src))
         dest->vtable->blit_from_system(src, dest, s_x, s_y, d_x, d_y, w, h);
      else
         dest->vtable->blit_from_memory(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else if (is_system_bitmap(dest)) {
      /* drawing onto system bitmaps */
      if (is_video_bitmap(src))
         src->vtable->blit_to_system(src, dest, s_x, s_y, d_x, d_y, w, h);
      else if (is_system_bitmap(src))
         dest->vtable->blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
      else
         dest->vtable->blit_from_memory(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else {
      /* drawing onto memory bitmaps */
      if ((is_video_bitmap(src)) || (is_system_bitmap(src)))
         src->vtable->blit_to_memory(src, dest, s_x, s_y, d_x, d_y, w, h);
      else
         dest->vtable->blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
}

END_OF_FUNCTION(al_blit);


/* al_blit_region:
 * Copies a rectangular area of the source bitmap to the destination bitmap.
 * The dest_x and dest_y are the coordinates of the top-left corner in the
 * destination bitmap where the source bitmap will be drawn.
 */
void al_blit_region(int method, BITMAP *src, int s_x, int s_y, int w, int h, BITMAP *dest, int d_x, int d_y)
{
   ASSERT(src);
   ASSERT(dest);
   BLIT_CLIP();
   
   /* Masked blit */
   if (method == AL_MASK_SOURCE) {
      ASSERT(src->vtable->color_depth == dest->vtable->color_depth);

      dest->vtable->masked_blit(src, dest, s_x, s_y, d_x, d_y, w, h);
      return;
   }

   if (src->vtable->color_depth != dest->vtable->color_depth) {
      /* need to do a color conversion */
      dest->vtable->blit_between_formats(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else if (is_same_bitmap(src, dest)) {
      /* special handling for overlapping regions */
      blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else if (is_video_bitmap(dest)) {
      /* drawing onto video bitmaps */
      if (is_video_bitmap(src))
         dest->vtable->blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
      else if (is_system_bitmap(src))
         dest->vtable->blit_from_system(src, dest, s_x, s_y, d_x, d_y, w, h);
      else
         dest->vtable->blit_from_memory(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else if (is_system_bitmap(dest)) {
      /* drawing onto system bitmaps */
      if (is_video_bitmap(src))
         src->vtable->blit_to_system(src, dest, s_x, s_y, d_x, d_y, w, h);
      else if (is_system_bitmap(src))
         dest->vtable->blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
      else
         dest->vtable->blit_from_memory(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
   else {
      /* drawing onto memory bitmaps */
      if ((is_video_bitmap(src)) || (is_system_bitmap(src)))
         src->vtable->blit_to_memory(src, dest, s_x, s_y, d_x, d_y, w, h);
      else
         dest->vtable->blit_to_self(src, dest, s_x, s_y, d_x, d_y, w, h);
   }
}

END_OF_FUNCTION(al_blit_region);
