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SDL_rotozoom.c

/*  

SDL_rotozoom.c - rotozoomer for 32bit or 8bit surfaces

LGPL (c) A. Schiffler

*/

#ifdef WIN32
#include <windows.h>
#endif

#include <stdlib.h>
#include <string.h>

#include "SDL_rotozoom.h"

#define MAX(a,b)    (((a) > (b)) ? (a) : (b))
#define MIN(a,b)    (((a) < (b)) ? (a) : (b))


/* 

32bit Zoomer with optional anti-aliasing by bilinear interpolation.

Zoomes 32bit RGBA/ABGR 'src' surface to 'dst' surface.

*/

int zoomSurfaceRGBA(SDL_Surface * src, SDL_Surface * dst, int smooth)
{
  int x, y, sx, sy, *sax, *say, *csax, *csay, csx, csy, ex, ey, t1, t2, sstep;
  tColorRGBA *c00, *c01, *c10, *c11;
  tColorRGBA *sp, *csp, *dp;
  int sgap, dgap;

  /*
  * Variable setup 
  */
  if (smooth) {
    /*
    * For interpolation: assume source dimension is one pixel 
    */
    /*
    * smaller to avoid overflow on right and bottom edge.     
    */
    sx = (int) (65536.0 * (float) (src->w - 1) / (float) dst->w);
    sy = (int) (65536.0 * (float) (src->h - 1) / (float) dst->h);
  } else {
    sx = (int) (65536.0 * (float) src->w / (float) dst->w);
    sy = (int) (65536.0 * (float) src->h / (float) dst->h);
  }

  /*
  * Allocate memory for row increments 
  */
  if ((sax = (int *) malloc((dst->w + 1) * sizeof(Uint32))) == NULL) {
    return (-1);
  }
  if ((say = (int *) malloc((dst->h + 1) * sizeof(Uint32))) == NULL) {
    free(sax);
    return (-1);
  }

  /*
  * Precalculate row increments 
  */
  csx = 0;
  csax = sax;
  for (x = 0; x <= dst->w; x++) {
    *csax = csx;
    csax++;
    csx &= 0xffff;
    csx += sx;
  }
  csy = 0;
  csay = say;
  for (y = 0; y <= dst->h; y++) {
    *csay = csy;
    csay++;
    csy &= 0xffff;
    csy += sy;
  }

  /*
  * Pointer setup 
  */
  sp = csp = (tColorRGBA *) src->pixels;
  dp = (tColorRGBA *) dst->pixels;
  sgap = src->pitch - src->w * 4;
  dgap = dst->pitch - dst->w * 4;

  /*
  * Switch between interpolating and non-interpolating code 
  */
  if (smooth) {

    /*
    * Interpolating Zoom 
    */

    /*
    * Scan destination 
    */
    csay = say;
    for (y = 0; y < dst->h; y++) {
      /*
      * Setup color source pointers 
      */
      c00 = csp;
      c01 = csp;
      c01++;
      c10 = (tColorRGBA *) ((Uint8 *) csp + src->pitch);
      c11 = c10;
      c11++;
      csax = sax;
      for (x = 0; x < dst->w; x++) {

        /*
        * Interpolate colors 
        */
        ex = (*csax & 0xffff);
        ey = (*csay & 0xffff);
        t1 = ((((c01->r - c00->r) * ex) >> 16) + c00->r) & 0xff;
        t2 = ((((c11->r - c10->r) * ex) >> 16) + c10->r) & 0xff;
        dp->r = (((t2 - t1) * ey) >> 16) + t1;
        t1 = ((((c01->g - c00->g) * ex) >> 16) + c00->g) & 0xff;
        t2 = ((((c11->g - c10->g) * ex) >> 16) + c10->g) & 0xff;
        dp->g = (((t2 - t1) * ey) >> 16) + t1;
        t1 = ((((c01->b - c00->b) * ex) >> 16) + c00->b) & 0xff;
        t2 = ((((c11->b - c10->b) * ex) >> 16) + c10->b) & 0xff;
        dp->b = (((t2 - t1) * ey) >> 16) + t1;
        t1 = ((((c01->a - c00->a) * ex) >> 16) + c00->a) & 0xff;
        t2 = ((((c11->a - c10->a) * ex) >> 16) + c10->a) & 0xff;
        dp->a = (((t2 - t1) * ey) >> 16) + t1;

        /*
        * Advance source pointers 
        */
        csax++;
        sstep = (*csax >> 16);
        c00 += sstep;
        c01 += sstep;
        c10 += sstep;
        c11 += sstep;
        /*
        * Advance destination pointer 
        */
        dp++;
      }
      /*
      * Advance source pointer 
      */
      csay++;
      csp = (tColorRGBA *) ((Uint8 *) csp + (*csay >> 16) * src->pitch);
      /*
      * Advance destination pointers 
      */
      dp = (tColorRGBA *) ((Uint8 *) dp + dgap);
    }

  } else {

    /*
    * Non-Interpolating Zoom 
    */

    csay = say;
    for (y = 0; y < dst->h; y++) {
      sp = csp;
      csax = sax;
      for (x = 0; x < dst->w; x++) {
        /*
        * Draw 
        */
        *dp = *sp;
        /*
        * Advance source pointers 
        */
        csax++;
        sp += (*csax >> 16);
        /*
        * Advance destination pointer 
        */
        dp++;
      }
      /*
      * Advance source pointer 
      */
      csay++;
      csp = (tColorRGBA *) ((Uint8 *) csp + (*csay >> 16) * src->pitch);
      /*
      * Advance destination pointers 
      */
      dp = (tColorRGBA *) ((Uint8 *) dp + dgap);
    }

  }

  /*
  * Remove temp arrays 
  */
  free(sax);
  free(say);

  return (0);
}

/* 

8bit Zoomer without smoothing.

Zoomes 8bit palette/Y 'src' surface to 'dst' surface.

*/

int zoomSurfaceY(SDL_Surface * src, SDL_Surface * dst)
{
  Uint32 x, y, sx, sy, *sax, *say, *csax, *csay, csx, csy;
  Uint8 *sp, *dp, *csp;
  int dgap;

  /*
  * Variable setup 
  */
  sx = (Uint32) (65536.0 * (float) src->w / (float) dst->w);
  sy = (Uint32) (65536.0 * (float) src->h / (float) dst->h);

  /*
  * Allocate memory for row increments 
  */
  if ((sax = (Uint32 *) malloc(dst->w * sizeof(Uint32))) == NULL) {
    return (-1);
  }
  if ((say = (Uint32 *) malloc(dst->h * sizeof(Uint32))) == NULL) {
    if (sax != NULL) {
      free(sax);
    }
    return (-1);
  }

  /*
  * Precalculate row increments 
  */
  csx = 0;
  csax = sax;
  for (x = 0; x < dst->w; x++) {
    csx += sx;
    *csax = (csx >> 16);
    csx &= 0xffff;
    csax++;
  }
  csy = 0;
  csay = say;
  for (y = 0; y < dst->h; y++) {
    csy += sy;
    *csay = (csy >> 16);
    csy &= 0xffff;
    csay++;
  }

  csx = 0;
  csax = sax;
  for (x = 0; x < dst->w; x++) {
    csx += (*csax);
    csax++;
  }
  csy = 0;
  csay = say;
  for (y = 0; y < dst->h; y++) {
    csy += (*csay);
    csay++;
  }

  /*
  * Pointer setup 
  */
  sp = csp = (Uint8 *) src->pixels;
  dp = (Uint8 *) dst->pixels;
  dgap = dst->pitch - dst->w;

  /*
  * Draw 
  */
  csay = say;
  for (y = 0; y < dst->h; y++) {
    csax = sax;
    sp = csp;
    for (x = 0; x < dst->w; x++) {
      /*
      * Draw 
      */
      *dp = *sp;
      /*
      * Advance source pointers 
      */
      sp += (*csax);
      csax++;
      /*
      * Advance destination pointer 
      */
      dp++;
    }
    /*
    * Advance source pointer (for row) 
    */
    csp += ((*csay) * src->pitch);
    csay++;
    /*
    * Advance destination pointers 
    */
    dp += dgap;
  }

  /*
  * Remove temp arrays 
  */
  free(sax);
  free(say);

  return (0);
}

/* 

32bit Rotozoomer with optional anti-aliasing by bilinear interpolation.

Rotates and zoomes 32bit RGBA/ABGR 'src' surface to 'dst' surface.

*/

void transformSurfaceRGBA(SDL_Surface * src, SDL_Surface * dst, int cx, int cy, int isin, int icos, int smooth)
{
  int x, y, t1, t2, dx, dy, xd, yd, sdx, sdy, ax, ay, ex, ey, sw, sh;
  tColorRGBA c00, c01, c10, c11;
  tColorRGBA *pc, *sp;
  int gap;

  /*
  * Variable setup 
  */
  xd = ((src->w - dst->w) << 15);
  yd = ((src->h - dst->h) << 15);
  ax = (cx << 16) - (icos * cx);
  ay = (cy << 16) - (isin * cx);
  sw = src->w - 1;
  sh = src->h - 1;
  pc = (tColorRGBA*)dst->pixels;
  gap = dst->pitch - dst->w * 4;

  /*
  * Switch between interpolating and non-interpolating code 
  */
  if (smooth) {
    for (y = 0; y < dst->h; y++) {
      dy = cy - y;
      sdx = (ax + (isin * dy)) + xd;
      sdy = (ay - (icos * dy)) + yd;
      for (x = 0; x < dst->w; x++) {
        dx = (sdx >> 16);
        dy = (sdy >> 16);
        if ((dx >= -1) && (dy >= -1) && (dx < src->w) && (dy < src->h)) {
          if ((dx >= 0) && (dy >= 0) && (dx < sw) && (dy < sh)) {
            sp = (tColorRGBA *) ((Uint8 *) src->pixels + src->pitch * dy);
            sp += dx;
            c00 = *sp;
            sp += 1;
            c01 = *sp;
            sp = (tColorRGBA *) ((Uint8 *) sp + src->pitch);
            sp -= 1;
            c10 = *sp;
            sp += 1;
            c11 = *sp;
          } else if ((dx == sw) && (dy == sh)) {
            sp = (tColorRGBA *) ((Uint8 *) src->pixels + src->pitch * dy);
            sp += dx;
            c00 = *sp;
            c01 = *sp;
            c10 = *sp;
            c11 = *sp;
          } else if ((dx == -1) && (dy == -1)) {
            sp = (tColorRGBA *) (src->pixels);
            c00 = *sp;
            c01 = *sp;
            c10 = *sp;
            c11 = *sp;
          } else if ((dx == -1) && (dy == sh)) {
            sp = (tColorRGBA *) (src->pixels);
            sp = (tColorRGBA *) ((Uint8 *) src->pixels + src->pitch * dy);
            c00 = *sp;
            c01 = *sp;
            c10 = *sp;
            c11 = *sp;
          } else if ((dx == sw) && (dy == -1)) {
            sp = (tColorRGBA *) (src->pixels);
            sp += dx;
            c00 = *sp;
            c01 = *sp;
            c10 = *sp;
            c11 = *sp;
          } else if (dx == -1) {
            sp = (tColorRGBA *) ((Uint8 *) src->pixels + src->pitch * dy);
            c00 = *sp;
            c01 = *sp;
            c10 = *sp;
            sp = (tColorRGBA *) ((Uint8 *) sp + src->pitch);
            c11 = *sp;
          } else if (dy == -1) {
            sp = (tColorRGBA *) (src->pixels);
            sp += dx;
            c00 = *sp;
            c01 = *sp;
            c10 = *sp;
            sp += 1;
            c11 = *sp;
          } else if (dx == sw) {
            sp = (tColorRGBA *) ((Uint8 *) src->pixels + src->pitch * dy);
            sp += dx;
            c00 = *sp;
            c01 = *sp;
            sp = (tColorRGBA *) ((Uint8 *) sp + src->pitch);
            c10 = *sp;
            c11 = *sp;
          } else if (dy == sh) {
            sp = (tColorRGBA *) ((Uint8 *) src->pixels + src->pitch * dy);
            sp += dx;
            c00 = *sp;
            sp += 1;
            c01 = *sp;
            c10 = *sp;
            c11 = *sp;
          }
          /*
          * Interpolate colors 
          */
          ex = (sdx & 0xffff);
          ey = (sdy & 0xffff);
          t1 = ((((c01.r - c00.r) * ex) >> 16) + c00.r) & 0xff;
          t2 = ((((c11.r - c10.r) * ex) >> 16) + c10.r) & 0xff;
          pc->r = (((t2 - t1) * ey) >> 16) + t1;
          t1 = ((((c01.g - c00.g) * ex) >> 16) + c00.g) & 0xff;
          t2 = ((((c11.g - c10.g) * ex) >> 16) + c10.g) & 0xff;
          pc->g = (((t2 - t1) * ey) >> 16) + t1;
          t1 = ((((c01.b - c00.b) * ex) >> 16) + c00.b) & 0xff;
          t2 = ((((c11.b - c10.b) * ex) >> 16) + c10.b) & 0xff;
          pc->b = (((t2 - t1) * ey) >> 16) + t1;
          t1 = ((((c01.a - c00.a) * ex) >> 16) + c00.a) & 0xff;
          t2 = ((((c11.a - c10.a) * ex) >> 16) + c10.a) & 0xff;
          pc->a = (((t2 - t1) * ey) >> 16) + t1;
        }
        sdx += icos;
        sdy += isin;
        pc++;
      }
      pc = (tColorRGBA *) ((Uint8 *) pc + gap);
    }
  } else {
    for (y = 0; y < dst->h; y++) {
      dy = cy - y;
      sdx = (ax + (isin * dy)) + xd;
      sdy = (ay - (icos * dy)) + yd;
      for (x = 0; x < dst->w; x++) {
        dx = (short) (sdx >> 16);
        dy = (short) (sdy >> 16);
        if ((dx >= 0) && (dy >= 0) && (dx < src->w) && (dy < src->h)) {
          sp = (tColorRGBA *) ((Uint8 *) src->pixels + src->pitch * dy);
          sp += dx;
          *pc = *sp;
        }
        sdx += icos;
        sdy += isin;
        pc++;
      }
      pc = (tColorRGBA *) ((Uint8 *) pc + gap);
    }
  }
}

/* 

8bit Rotozoomer without smoothing

Rotates and zoomes 8bit palette/Y 'src' surface to 'dst' surface.

*/

void transformSurfaceY(SDL_Surface * src, SDL_Surface * dst, int cx, int cy, int isin, int icos)
{
  int x, y, dx, dy, xd, yd, sdx, sdy, ax, ay, sw, sh;
  tColorY *pc, *sp;
  int gap;

  /*
  * Variable setup 
  */
  xd = ((src->w - dst->w) << 15);
  yd = ((src->h - dst->h) << 15);
  ax = (cx << 16) - (icos * cx);
  ay = (cy << 16) - (isin * cx);
  sw = src->w - 1;
  sh = src->h - 1;
  pc = (tColorY*)dst->pixels;
  gap = dst->pitch - dst->w;
  /*
  * Clear surface to colorkey 
  */
  memset(pc, (unsigned char) (src->format->colorkey & 0xff), dst->pitch * dst->h);
  /*
  * Iterate through destination surface 
  */
  for (y = 0; y < dst->h; y++) {
    dy = cy - y;
    sdx = (ax + (isin * dy)) + xd;
    sdy = (ay - (icos * dy)) + yd;
    for (x = 0; x < dst->w; x++) {
      dx = (short) (sdx >> 16);
      dy = (short) (sdy >> 16);
      if ((dx >= 0) && (dy >= 0) && (dx < src->w) && (dy < src->h)) {
        sp = (tColorY *) (src->pixels);
        sp += (src->pitch * dy + dx);
        *pc = *sp;
      }
      sdx += icos;
      sdy += isin;
      pc++;
    }
    pc += gap;
  }
}

/* 

rotozoomSurface()

Rotates and zoomes a 32bit or 8bit 'src' surface to newly created 'dst' surface.
'angle' is the rotation in degrees. 'zoom' a scaling factor. If 'smooth' is 1
then the destination 32bit surface is anti-aliased. If the surface is not 8bit
or 32bit RGBA/ABGR it will be converted into a 32bit RGBA format on the fly.

*/

#define VALUE_LIMIT     0.001


/* Local rotozoom-size function with trig result return */

void rotozoomSurfaceSizeTrig(int width, int height, double angle, double zoom, int *dstwidth, int *dstheight,
                             double *canglezoom, double *sanglezoom)
{
  double x, y, cx, cy, sx, sy;
  double radangle;
  int dstwidthhalf, dstheighthalf;

  /*
  * Determine destination width and height by rotating a centered source box 
  */
  radangle = angle * (M_PI / 180.0);
  *sanglezoom = sin(radangle);
  *canglezoom = cos(radangle);
  *sanglezoom *= zoom;
  *canglezoom *= zoom;
  x = width / 2;
  y = height / 2;
  cx = *canglezoom * x;
  cy = *canglezoom * y;
  sx = *sanglezoom * x;
  sy = *sanglezoom * y;
  dstwidthhalf = MAX((int)
    ceil(MAX(MAX(MAX(fabs(cx + sy), fabs(cx - sy)), fabs(-cx + sy)), fabs(-cx - sy))), 1);
  dstheighthalf = MAX((int)
    ceil(MAX(MAX(MAX(fabs(sx + cy), fabs(sx - cy)), fabs(-sx + cy)), fabs(-sx - cy))), 1);
  *dstwidth = 2 * dstwidthhalf;
  *dstheight = 2 * dstheighthalf;
}


/* Publically available rotozoom-size function */

void rotozoomSurfaceSize(int width, int height, double angle, double zoom, int *dstwidth, int *dstheight)
{
  double dummy_sanglezoom, dummy_canglezoom;

  rotozoomSurfaceSizeTrig(width, height, angle, zoom, dstwidth, dstheight, &dummy_sanglezoom, &dummy_canglezoom);
}


/* Publically available rotozoom function */

SDL_Surface *rotozoomSurface(SDL_Surface * src, double angle, double zoom, int smooth)
{
  SDL_Surface *rz_src;
  SDL_Surface *rz_dst;
  double zoominv;
  double sanglezoom, canglezoom, sanglezoominv, canglezoominv;
  int dstwidthhalf, dstwidth, dstheighthalf, dstheight;
  int is32bit;
  int i, src_converted;

  /*
  * Sanity check 
  */
  if (src == NULL)
    return (NULL);

  /*
  * Determine if source surface is 32bit or 8bit 
  */
  is32bit = (src->format->BitsPerPixel == 32);
  if ((is32bit) || (src->format->BitsPerPixel == 8)) {
    /*
    * Use source surface 'as is' 
    */
    rz_src = src;
    src_converted = 0;
  } else {
    /*
    * New source surface is 32bit with a defined RGBA ordering 
    */
    rz_src =
      SDL_CreateRGBSurface(SDL_SWSURFACE, src->w, src->h, 32, 0x000000ff, 0x0000ff00, 0x00ff0000, 0xff000000);
    SDL_BlitSurface(src, NULL, rz_src, NULL);
    src_converted = 1;
    is32bit = 1;
  }

  /*
  * Sanity check zoom factor 
  */
  if (zoom < VALUE_LIMIT) {
    zoom = VALUE_LIMIT;
  }
  zoominv = 65536.0 / (zoom * zoom);

  /*
  * Check if we have a rotozoom or just a zoom 
  */
  if (fabs(angle) > VALUE_LIMIT) {

    /*
    * Angle!=0: full rotozoom 
    */
    /*
    * ----------------------- 
    */

    /* Determine target size */
    rotozoomSurfaceSizeTrig(rz_src->w, rz_src->h, angle, zoom, &dstwidth, &dstheight, &canglezoom, &sanglezoom);

    /*
    * Calculate target factors from sin/cos and zoom 
    */
    sanglezoominv = sanglezoom;
    canglezoominv = canglezoom;
    sanglezoominv *= zoominv;
    canglezoominv *= zoominv;

    /* Calculate half size */
    dstwidthhalf = dstwidth / 2;
    dstheighthalf = dstheight / 2;

    /*
    * Alloc space to completely contain the rotated surface 
    */
    rz_dst = NULL;
    if (is32bit) {
      /*
      * Target surface is 32bit with source RGBA/ABGR ordering 
      */
      rz_dst =
        SDL_CreateRGBSurface(SDL_SWSURFACE, dstwidth, dstheight, 32,
        rz_src->format->Rmask, rz_src->format->Gmask,
        rz_src->format->Bmask, rz_src->format->Amask);
    } else {
      /*
      * Target surface is 8bit 
      */
      rz_dst = SDL_CreateRGBSurface(SDL_SWSURFACE, dstwidth, dstheight, 8, 0, 0, 0, 0);
    }

    /*
    * Lock source surface 
    */
    SDL_LockSurface(rz_src);
    /*
    * Check which kind of surface we have 
    */
    if (is32bit) {
      /*
      * Call the 32bit transformation routine to do the rotation (using alpha) 
      */
      transformSurfaceRGBA(rz_src, rz_dst, dstwidthhalf, dstheighthalf,
        (int) (sanglezoominv), (int) (canglezoominv), smooth);
      /*
      * Turn on source-alpha support 
      */
      SDL_SetAlpha(rz_dst, SDL_SRCALPHA, 255);
    } else {
      /*
      * Copy palette and colorkey info 
      */
      for (i = 0; i < rz_src->format->palette->ncolors; i++) {
        rz_dst->format->palette->colors[i] = rz_src->format->palette->colors[i];
      }
      rz_dst->format->palette->ncolors = rz_src->format->palette->ncolors;
      /*
      * Call the 8bit transformation routine to do the rotation 
      */
      transformSurfaceY(rz_src, rz_dst, dstwidthhalf, dstheighthalf,
        (int) (sanglezoominv), (int) (canglezoominv));
      SDL_SetColorKey(rz_dst, SDL_SRCCOLORKEY | SDL_RLEACCEL, rz_src->format->colorkey);
    }
    /*
    * Unlock source surface 
    */
    SDL_UnlockSurface(rz_src);

  } else {

    /*
    * Angle=0: Just a zoom 
    */
    /*
    * -------------------- 
    */

    /*
    * Calculate target size
    */
    zoomSurfaceSize(rz_src->w, rz_src->h, zoom, zoom, &dstwidth, &dstheight);

    /*
    * Alloc space to completely contain the zoomed surface 
    */
    rz_dst = NULL;
    if (is32bit) {
      /*
      * Target surface is 32bit with source RGBA/ABGR ordering 
      */
      rz_dst =
        SDL_CreateRGBSurface(SDL_SWSURFACE, dstwidth, dstheight, 32,
        rz_src->format->Rmask, rz_src->format->Gmask,
        rz_src->format->Bmask, rz_src->format->Amask);
    } else {
      /*
      * Target surface is 8bit 
      */
      rz_dst = SDL_CreateRGBSurface(SDL_SWSURFACE, dstwidth, dstheight, 8, 0, 0, 0, 0);
    }

    /*
    * Lock source surface 
    */
    SDL_LockSurface(rz_src);
    /*
    * Check which kind of surface we have 
    */
    if (is32bit) {
      /*
      * Call the 32bit transformation routine to do the zooming (using alpha) 
      */
      zoomSurfaceRGBA(rz_src, rz_dst, smooth);
      /*
      * Turn on source-alpha support 
      */
      SDL_SetAlpha(rz_dst, SDL_SRCALPHA, 255);
    } else {
      /*
      * Copy palette and colorkey info 
      */
      for (i = 0; i < rz_src->format->palette->ncolors; i++) {
        rz_dst->format->palette->colors[i] = rz_src->format->palette->colors[i];
      }
      rz_dst->format->palette->ncolors = rz_src->format->palette->ncolors;
      /*
      * Call the 8bit transformation routine to do the zooming 
      */
      zoomSurfaceY(rz_src, rz_dst);
      SDL_SetColorKey(rz_dst, SDL_SRCCOLORKEY | SDL_RLEACCEL, rz_src->format->colorkey);
    }
    /*
    * Unlock source surface 
    */
    SDL_UnlockSurface(rz_src);
  }

  /*
  * Cleanup temp surface 
  */
  if (src_converted) {
    SDL_FreeSurface(rz_src);
  }

  /*
  * Return destination surface 
  */
  return (rz_dst);
}

/* 

zoomSurface()

Zoomes a 32bit or 8bit 'src' surface to newly created 'dst' surface.
'zoomx' and 'zoomy' are scaling factors for width and height. If 'smooth' is 1
then the destination 32bit surface is anti-aliased. If the surface is not 8bit
or 32bit RGBA/ABGR it will be converted into a 32bit RGBA format on the fly.

*/

#define VALUE_LIMIT     0.001

void zoomSurfaceSize(int width, int height, double zoomx, double zoomy, int *dstwidth, int *dstheight)
{
  /*
  * Sanity check zoom factors 
  */
  if (zoomx < VALUE_LIMIT) {
    zoomx = VALUE_LIMIT;
  }
  if (zoomy < VALUE_LIMIT) {
    zoomy = VALUE_LIMIT;
  }

  /*
  * Calculate target size 
  */
  *dstwidth = (int) ((double) width * zoomx);
  *dstheight = (int) ((double) height * zoomy);
  if (*dstwidth < 1) {
    *dstwidth = 1;
  }
  if (*dstheight < 1) {
    *dstheight = 1;
  }
}

SDL_Surface *zoomSurface(SDL_Surface * src, double zoomx, double zoomy, int smooth)
{
  SDL_Surface *rz_src;
  SDL_Surface *rz_dst;
  int dstwidth, dstheight;
  int is32bit;
  int i, src_converted;

  /*
  * Sanity check 
  */
  if (src == NULL)
    return (NULL);

  /*
  * Determine if source surface is 32bit or 8bit 
  */
  is32bit = (src->format->BitsPerPixel == 32);
  if ((is32bit) || (src->format->BitsPerPixel == 8)) {
    /*
    * Use source surface 'as is' 
    */
    rz_src = src;
    src_converted = 0;
  } else {
    /*
    * New source surface is 32bit with a defined RGBA ordering 
    */
    rz_src =
      SDL_CreateRGBSurface(SDL_SWSURFACE, src->w, src->h, 32, 0x000000ff, 0x0000ff00, 0x00ff0000, 0xff000000);
    SDL_BlitSurface(src, NULL, rz_src, NULL);
    src_converted = 1;
    is32bit = 1;
  }

  /* Get size if target */
  zoomSurfaceSize(rz_src->w, rz_src->h, zoomx, zoomy, &dstwidth, &dstheight);

  /*
  * Alloc space to completely contain the zoomed surface 
  */
  rz_dst = NULL;
  if (is32bit) {
    /*
    * Target surface is 32bit with source RGBA/ABGR ordering 
    */
    rz_dst =
      SDL_CreateRGBSurface(SDL_SWSURFACE, dstwidth, dstheight, 32,
      rz_src->format->Rmask, rz_src->format->Gmask,
      rz_src->format->Bmask, rz_src->format->Amask);
  } else {
    /*
    * Target surface is 8bit 
    */
    rz_dst = SDL_CreateRGBSurface(SDL_SWSURFACE, dstwidth, dstheight, 8, 0, 0, 0, 0);
  }

  /*
  * Lock source surface 
  */
  SDL_LockSurface(rz_src);
  /*
  * Check which kind of surface we have 
  */
  if (is32bit) {
    /*
    * Call the 32bit transformation routine to do the zooming (using alpha) 
    */
    zoomSurfaceRGBA(rz_src, rz_dst, smooth);
    /*
    * Turn on source-alpha support 
    */
    SDL_SetAlpha(rz_dst, SDL_SRCALPHA, 255);
  } else {
    /*
    * Copy palette and colorkey info 
    */
    for (i = 0; i < rz_src->format->palette->ncolors; i++) {
      rz_dst->format->palette->colors[i] = rz_src->format->palette->colors[i];
    }
    rz_dst->format->palette->ncolors = rz_src->format->palette->ncolors;
    /*
    * Call the 8bit transformation routine to do the zooming 
    */
    zoomSurfaceY(rz_src, rz_dst);
    SDL_SetColorKey(rz_dst, SDL_SRCCOLORKEY | SDL_RLEACCEL, rz_src->format->colorkey);
  }
  /*
  * Unlock source surface 
  */
  SDL_UnlockSurface(rz_src);

  /*
  * Cleanup temp surface 
  */
  if (src_converted) {
    SDL_FreeSurface(rz_src);
  }

  /*
  * Return destination surface 
  */
  return (rz_dst);
}

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