mipmap.c

/*
	DDS GIMP plugin

	Copyright (C) 2004-2012 Shawn Kirst <skirst@gmail.com>,
   with parts (C) 2003 Arne Reuter <homepage@arnereuter.de> where specified.

	This program is free software; you can redistribute it and/or
	modify it under the terms of the GNU General Public
	License as published by the Free Software Foundation; either
	version 2 of the License, or (at your option) any later version.

	This program 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
	General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program; see the file COPYING.  If not, write to
	the Free Software Foundation, 51 Franklin Street, Fifth Floor
	Boston, MA 02110-1301, USA.
*/

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

#include <gtk/gtk.h>

#ifdef _OPENMP
#include <omp.h>
#endif

#include "dds.h"
#include "mipmap.h"
#include "imath.h"
#include "color.h"

typedef float (*filterfunc_t)(float);
typedef int   (*wrapfunc_t)(int, int);
typedef void  (*mipmapfunc_t)(unsigned char *, int, int, unsigned char *, int, int, int, filterfunc_t, float, wrapfunc_t, int, float);
typedef void  (*volmipmapfunc_t)(unsigned char *, int, int, int, unsigned char *, int, int, int, int, filterfunc_t, float, wrapfunc_t, int, float);

/******************************************************************************
 * size functions                                                             *
 ******************************************************************************/

int get_num_mipmaps(int width, int height)
{
   int w = width << 1;
   int h = height << 1;
   int n = 0;

   while(w != 1 || h != 1)
   {
      if(w > 1) w >>= 1;
      if(h > 1) h >>= 1;
      ++n;
   }

   return(n);
}

unsigned int get_mipmapped_size(int width, int height, int bpp,
                                int level, int num, int format)
{
   int w, h, n = 0;
   unsigned int size = 0;

   w = width >> level;
   h = height >> level;
   w = MAX(1, w);
   h = MAX(1, h);
   w <<= 1;
   h <<= 1;

   while(n < num && (w != 1 || h != 1))
   {
      if(w > 1) w >>= 1;
      if(h > 1) h >>= 1;
      if(format == DDS_COMPRESS_NONE)
         size += (w * h);
      else
         size += ((w + 3) >> 2) * ((h + 3) >> 2);
      ++n;
   }

   if(format == DDS_COMPRESS_NONE)
      size *= bpp;
   else
   {
      if(format == DDS_COMPRESS_BC1 || format == DDS_COMPRESS_BC4)
         size *= 8;
      else
         size *= 16;
   }

   return(size);
}

unsigned int get_volume_mipmapped_size(int width, int height,
                                       int depth, int bpp, int level,
                                       int num, int format)
{
   int w, h, d, n = 0;
   unsigned int size = 0;

   w = width >> level;
   h = height >> level;
   d = depth >> level;
   w = MAX(1, w);
   h = MAX(1, h);
   d = MAX(1, d);
   w <<= 1;
   h <<= 1;
   d <<= 1;

   while(n < num && (w != 1 || h != 1))
   {
      if(w > 1) w >>= 1;
      if(h > 1) h >>= 1;
      if(d > 1) d >>= 1;
      if(format == DDS_COMPRESS_NONE)
         size += (w * h * d);
      else
         size += (((w + 3) >> 2) * ((h + 3) >> 2) * d);
      ++n;
   }

   if(format == DDS_COMPRESS_NONE)
      size *= bpp;
   else
   {
      if(format == DDS_COMPRESS_BC1 || format == DDS_COMPRESS_BC4)
         size *= 8;
      else
         size *= 16;
   }

   return(size);
}

int get_next_mipmap_dimensions(int *next_w, int *next_h,
                               int  curr_w, int  curr_h)
{
   if(curr_w == 1 || curr_h == 1)
      return(0);

   if(next_w) *next_w = curr_w >> 1;
   if(next_h) *next_h = curr_h >> 1;

   return(1);
}

/******************************************************************************
 * wrap modes                                                                 *
 ******************************************************************************/

static int wrap_mirror(int x, int max)
{
   if(max == 1) x = 0;
   x = abs(x);
   while(x >= max)
      x = abs(max + max - x - 2);
   return(x);
}

static int wrap_repeat(int x, int max)
{
   if(x >= 0) return(x % max);
   return((x + 1) % max + max - 1);
}

static int wrap_clamp(int x, int max)
{
   return(MAX(0, MIN(max - 1, x)));
}

/******************************************************************************
 * gamma-correction                                                           *
 ******************************************************************************/

static int linear_to_gamma(int gc, int v, float gamma)
{
   if(gc == 1)
   {
      v = (int)(powf((float)v / 255.0f, gamma) * 255);
      if(v > 255) v = 255;
   }
   else if(gc == 2)
      v = linear_to_sRGB(v);

   return(v);
}

static int gamma_to_linear(int gc, int v, float gamma)
{
   if(gc == 1)
   {
      v = (int)(powf((float)v / 255.0f, 1.0f / gamma) * 255);
      if(v > 255) v = 255;
   }
   else if(gc == 2)
      v = sRGB_to_linear(v);

   return(v);
}

/******************************************************************************
 * filters                                                                    *
 ******************************************************************************/

static float box_filter(float t)
{
   if((t >= -0.5f) && (t < 0.5f))
      return(1.0f);

   return(0.0f);
}

static float triangle_filter(float t)
{
   if(t < 0.0f) t = -t;
   if(t < 1.0f) return(1.0f - t);
   return(0.0f);
}

static float quadratic_filter(float t)
{
   if(t < 0.0f) t = -t;
   if(t < 0.5f) return(0.75f - t * t);
   if(t < 1.5f)
   {
      t -= 1.5f;
      return(0.5f * t * t);
   }
   return(0.0f);
}

static float bspline_filter(float t)
{
   float tt;

   if(t < 0.0f) t = -t;

   if(t < 1.0f)
   {
      tt = t * t;
      return(((0.5f * tt * t) - tt + (2.0f / 3.0f)));
   }
   else if(t < 2.0f)
   {
      t = 2.0f - t;
      return((1.0f / 6.0f) * (t * t * t));
   }

   return(0.0f);
}

static float mitchell(float t, const float B, const float C)
{
   float tt;

   tt = t * t;
   if(t < 0.0f) t = -t;

   if(t < 1.0f)
   {
      t = (((12.0f - 9.0f * B - 6.0f * C) * (t * tt)) +
         ((-18.0f + 12.0f * B + 6.0f * C) * tt) +
         (6.0f - 2.0f * B));
      return(t / 6.0f);
   }
   else if(t < 2.0f)
   {
      t = (((-1.0f * B - 6.0f * C) * (t * tt)) +
         ((6.0f * B + 30.0f * C) * tt) +
         ((-12.0f * B - 48.0f * C) * t) +
         (8.0f * B + 24.0f * C));
      return(t / 6.0f);
   }

   return(0.0f);
}

static float mitchell_filter(float t)
{
   return(mitchell(t, 1.0f / 3.0f, 1.0f / 3.0f));
}

static float sinc(float x)
{
   x = (x * M_PI);
   if(fabsf(x) < 1e-04f)
      return(1.0f + x * x * (-1.0f / 6.0f + x * x * 1.0f / 120.0f));

   return(sinf(x) / x);
}

static float lanczos_filter(float t)
{
   if(t < 0.0f) t = -t;
   if(t < 3.0f) return(sinc(t) * sinc(t / 3.0f));
   return(0.0f);
}

static float bessel0(float x)
{
   const float EPSILON = 1e-6f;
   float xh, sum, pow, ds;
   int k;

   xh = 0.5f * x;
   sum = 1.0f;
   pow = 1.0f;
   k = 0;
   ds = 1.0f;
   while(ds > sum * EPSILON)
   {
      ++k;
      pow = pow * (xh / k);
      ds = pow * pow;
      sum += ds;
   }

   return(sum);
}

static float kaiser_filter(float t)
{
   if(t < 0.0f) t = -t;

   if(t < 3.0f)
   {
      const float alpha = 4.0f;
      const float rb04 = 0.0884805322f; // 1.0f / bessel0(4.0f);
      const float ratio = t / 3.0f;
      if((1.0f - ratio * ratio) >= 0)
         return(sinc(t) * bessel0(alpha * sqrtf(1.0f - ratio * ratio)) * rb04);
   }
   return(0.0f);
}

/******************************************************************************
 * 2D image scaling                                                           *
 ******************************************************************************/

static void scale_image_nearest(unsigned char *dst, int dw, int dh,
                                unsigned char *src, int sw, int sh,
                                int bpp, filterfunc_t filter, float support,
                                wrapfunc_t wrap,
                                int gc, float gamma)
{
   int n, x, y;
   int ix, iy;
   int srowbytes = sw * bpp;
   int drowbytes = dw * bpp;

   for(y = 0; y < dh; ++y)
   {
      iy = (y * sh + sh / 2) / dh;
      for(x = 0; x < dw; ++x)
      {
         ix = (x * sw + sw / 2) / dw;
         for(n = 0; n < bpp; ++n)
         {
            dst[y * drowbytes + (x * bpp) + n] =
               src[iy * srowbytes + (ix * bpp) + n];
         }
      }
   }
}

static void scale_image(unsigned char *dst, int dw, int dh,
                        unsigned char *src, int sw, int sh,
                        int bpp, filterfunc_t filter, float support,
                        wrapfunc_t wrap,
                        int gc, float gamma)
{
   const float blur = 1.0f;
   const float xfactor = (float)dw / (float)sw;
   const float yfactor = (float)dh / (float)sh;

   int x, y, start, stop, nmax, n, i;
   int sstride = sw * bpp;
   float center, contrib, density, s, r, t;

   unsigned char *d, *row, *col;

   float xscale = MIN(xfactor, 1.0f) / blur;
   float yscale = MIN(yfactor, 1.0f) / blur;
   float xsupport = support / xscale;
   float ysupport = support / yscale;

   if(xsupport <= 0.5f)
   {
      xsupport = 0.5f + 1e-10f;
      xscale = 1.0f;
   }
   if(ysupport <= 0.5f)
   {
      ysupport = 0.5f + 1e-10f;
      yscale = 1.0f;
   }

   unsigned char *tmp;

#ifdef _OPENMP
   tmp = g_malloc(sw * bpp * omp_get_max_threads());
#else
   tmp = g_malloc(sw * bpp);
#endif

#ifdef _OPENMP
   #pragma omp parallel for schedule(dynamic) \
      private(x, y, d, row, col, center, start, stop, nmax, s, i, n, density, r, t, contrib)
#endif
   for(y = 0; y < dh; ++y)
   {
      /* resample in Y direction to temp buffer */
      d = tmp;
#ifdef _OPENMP
      d += (sw * bpp * omp_get_thread_num());
#endif

      center = ((float)y + 0.5f) / yfactor;
      start = (int)(center - ysupport + 0.5f);
      stop  = (int)(center + ysupport + 0.5f);
      nmax = stop - start;
      s = (float)start - center + 0.5f;

      for(x = 0; x < sw; ++x)
      {
         col = src + (x * bpp);

         for(i = 0; i < bpp; ++i)
         {
            density = 0.0f;
            r = 0.0f;

            for(n = 0; n < nmax; ++n)
            {
               contrib = filter((s + n) * yscale);
               density += contrib;
               if(i == 3)
                  t = col[(wrap(start + n, sh) * sstride) + i];
               else
                  t = linear_to_gamma(gc, col[(wrap(start + n, sh) * sstride) + i], gamma);
               r += t * contrib;
            }

            if(density != 0.0f && density != 1.0f)
               r /= density;

            r = MIN(255, MAX(0, r));

            if(i != 3)
               r = gamma_to_linear(gc, r, gamma);

            d[(x * bpp) + i] = (unsigned char)r;
         }
      }

      /* resample in X direction using temp buffer */
      row = d;
      d = dst;

      for(x = 0; x < dw; ++x)
      {
         center = ((float)x + 0.5f) / xfactor;
         start = (int)(center - xsupport + 0.5f);
         stop  = (int)(center + xsupport + 0.5f);
         nmax = stop - start;
         s = (float)start - center + 0.5f;

         for(i = 0; i < bpp; ++i)
         {
            density = 0.0f;
            r = 0.0f;

            for(n = 0; n < nmax; ++n)
            {
               contrib = filter((s + n) * xscale);
               density += contrib;
               if(i == 3)
                  t = row[(wrap(start + n, sw) * bpp) + i];
               else
                  t = linear_to_gamma(gc, row[(wrap(start + n, sw) * bpp) + i], gamma);
               r += t * contrib;
            }

            if(density != 0.0f && density != 1.0f)
               r /= density;

            r = MIN(255, MAX(0, r));

            if(i != 3)
               r = gamma_to_linear(gc, r, gamma);

            d[(y * (dw * bpp)) + (x * bpp) + i] = (unsigned char)r;
         }
      }
   }

   g_free(tmp);
}

/******************************************************************************
 * 3D image scaling                                                           *
 ******************************************************************************/

static void scale_volume_image_nearest(unsigned char *dst, int dw, int dh, int dd,
                                       unsigned char *src, int sw, int sh, int sd,
                                       int bpp, filterfunc_t filter, float support,
                                       wrapfunc_t wrap,
                                       int gc, float gamma)
{
   int n, x, y, z;
   int ix, iy, iz;

   for(z = 0; z < dd; ++z)
   {
      iz = (z * sd + sd / 2) / dd;
      for(y = 0; y < dh; ++y)
      {
         iy = (y * sh + sh / 2) / dh;
         for(x = 0; x < dw; ++x)
         {
            ix = (x * sw + sw / 2) / dw;
            for(n = 0; n < bpp; ++n)
            {
               dst[(z * (dw * dh)) + (y * dw) + (x * bpp) + n] =
                  src[(iz * (sw * sh)) + (iy * sw) + (ix * bpp) + n];
            }
         }
      }
   }
}

static void scale_volume_image(unsigned char *dst, int dw, int dh, int dd,
                               unsigned char *src, int sw, int sh, int sd,
                               int bpp, filterfunc_t filter, float support,
                               wrapfunc_t wrap,
                               int gc, float gamma)
{
   /* down to a 2D image, use the faster 2D image resampler */
   if(dd == 1 && sd == 1)
   {
      scale_image(dst, dw, dh, src, sw, sh, bpp, filter, support, wrap, gc, gamma);
      return;
   }

   const float blur = 1.0f;
   const float xfactor = (float)dw / (float)sw;
   const float yfactor = (float)dh / (float)sh;
   const float zfactor = (float)dd / (float)sd;

   int x, y, z, start, stop, nmax, n, i;
   int sstride = sw * bpp;
   int zstride = sh * sw * bpp;
   float center, contrib, density, s, r, t;

   unsigned char *d, *row, *col, *slice;

   float xscale = MIN(xfactor, 1.0f) / blur;
   float yscale = MIN(yfactor, 1.0f) / blur;
   float zscale = MIN(zfactor, 1.0f) / blur;
   float xsupport = support / xscale;
   float ysupport = support / yscale;
   float zsupport = support / zscale;

   if(xsupport <= 0.5f)
   {
      xsupport = 0.5f + 1e-10f;
      xscale = 1.0f;
   }
   if(ysupport <= 0.5f)
   {
      ysupport = 0.5f + 1e-10f;
      yscale = 1.0f;
   }
   if(zsupport <= 0.5f)
   {
      zsupport = 0.5f + 1e-10f;
      zscale = 1.0f;
   }

   unsigned char *tmp1, *tmp2;

   tmp1 = g_malloc(sh * sw * bpp);
   tmp2 = g_malloc(dh * sw * bpp);

   for(z = 0; z < dd; ++z)
   {
      /* resample in Z direction */
      d = tmp1;

      center = ((float)z + 0.5f) / zfactor;
      start = (int)(center - zsupport + 0.5f);
      stop =  (int)(center + zsupport + 0.5f);
      nmax = stop - start;
      s = (float)start - center + 0.5f;

      #ifdef _OPENMP
      #pragma omp parallel for schedule(dynamic) \
      private(x, y, slice, i, n, density, r, t, contrib)
      #endif
      for(y = 0; y < sh; ++y)
      {
         for(x = 0; x < sw; ++x)
         {
            slice = src + (y * (sw * bpp)) + (x * bpp);

            for(i = 0; i < bpp; ++i)
            {
               density = 0.0f;
               r = 0.0f;

               for(n = 0; n < nmax; ++n)
               {
                  contrib = filter((s + n) * zscale);
                  density += contrib;
                  if(i == 3)
                     t = slice[(wrap(start + n, sd) * zstride) + i];
                  else
                     t = linear_to_gamma(gc, slice[(wrap(start + n, sd) * zstride) + i], gamma);
                  r += t * contrib;
               }

               if(density != 0.0f && density != 1.0f)
                  r /= density;

               r = MIN(255, MAX(0, r));

               if(i != 3)
                  r = gamma_to_linear(gc, r, gamma);

               d[((y * sw) + x) * bpp + i] = (unsigned char)r;
            }
         }
      }

      /* resample in Y direction */
      d = tmp2;
      #ifdef _OPENMP
      #pragma omp parallel for schedule(dynamic) \
      private(x, y, col, center, start, stop, nmax, s, i, n, density, r, t, contrib)
      #endif
      for(y = 0; y < dh; ++y)
      {
         center = ((float)y + 0.5f) / yfactor;
         start = (int)(center - ysupport + 0.5f);
         stop =  (int)(center + ysupport + 0.5f);
         nmax = stop - start;
         s = (float)start - center + 0.5f;

         for(x = 0; x < sw; ++x)
         {
            col = tmp1 + (x * bpp);

            for(i = 0; i < bpp; ++i)
            {
               density = 0.0f;
               r = 0.0f;

               for(n = 0; n < nmax; ++n)
               {
                  contrib = filter((s + n) * yscale);
                  density += contrib;
                  if(i == 3)
                     t = col[(wrap(start + n, sh) * sstride) + i];
                  else
                     t = linear_to_gamma(gc, col[(wrap(start + n, sh) * sstride) + i], gamma);
                  r += t * contrib;
               }

               if(density != 0.0f && density != 1.0f)
                  r /= density;

               r = MIN(255, MAX(0, r));

               if(i != 3)
                  r = gamma_to_linear(gc, r, gamma);

               d[((y * sw) + x) * bpp + i] = (unsigned char)r;
            }
         }
      }

      /* resample in X direction */
      d = dst;
      #ifdef _OPENMP
      #pragma omp parallel for schedule(dynamic) \
      private(x, y, row, center, start, stop, nmax, s, i, n, density, r, t, contrib)
      #endif
      for(y = 0; y < dh; ++y)
      {
         row = tmp2 + (y * sstride);

         for(x = 0; x < dw; ++x)
         {
            center = ((float)x + 0.5f) / xfactor;
            start = (int)(center - xsupport + 0.5f);
            stop =  (int)(center + xsupport + 0.5f);
            nmax = stop - start;
            s = (float)start - center + 0.5f;

            for(i = 0; i < bpp; ++i)
            {
               density = 0.0f;
               r = 0.0f;

               for(n = 0; n < nmax; ++n)
               {
                  contrib = filter((s + n) * xscale);
                  density += contrib;
                  if(i == 3)
                     t = row[(wrap(start + n, sw) * bpp) + i];
                  else
                     t = linear_to_gamma(gc, row[(wrap(start + n, sw) * bpp) + i], gamma);
                  r += t * contrib;
               }

               if(density != 0.0f && density != 1.0f)
                  r /= density;

               r = MIN(255, MAX(0, r));

               if(i != 3)
                  r = gamma_to_linear(gc, r, gamma);

               d[((z * dh * dw) + (y * dw) + x) * bpp + i] = (unsigned char)r;
            }
         }
      }
   }

   g_free(tmp1);
   g_free(tmp2);
}

/******************************************************************************
 * filter lookup table                                                        *
 ******************************************************************************/

static struct
{
   int filter;
   filterfunc_t func;
   float support;
} filters[] =
{
   {DDS_MIPMAP_FILTER_BOX,       box_filter,       0.5f},
   {DDS_MIPMAP_FILTER_TRIANGLE,  triangle_filter,  1.0f},
   {DDS_MIPMAP_FILTER_QUADRATIC, quadratic_filter, 1.5f},
   {DDS_MIPMAP_FILTER_BSPLINE,   bspline_filter,   2.0f},
   {DDS_MIPMAP_FILTER_MITCHELL,  mitchell_filter,  2.0f},
   {DDS_MIPMAP_FILTER_LANCZOS,   lanczos_filter,   3.0f},
   {DDS_MIPMAP_FILTER_KAISER,    kaiser_filter,    3.0f},
   {DDS_MIPMAP_FILTER_MAX,       NULL,             0.0f}
};

/*
 * Alpha test coverage - portion of visible texels after alpha test:
 *   if (texel_alpha < alpha_test_threshold)
 *      discard;
 */
float calc_alpha_test_coverage(unsigned char *src,
                               unsigned int width, unsigned int height, int bpp,
                               float alpha_test_threshold,
                               float alpha_scale)
{
   unsigned int x, y;
   int rowbytes = width * bpp;
   int coverage = 0;
   const int alpha_channel_idx = 3;

   if(bpp <= alpha_channel_idx)
   {
      /* No alpha channel */
      return 1.f;
   }

   for(y = 0; y < height; ++y)
   {
      for(x = 0; x < width; ++x)
      {
         const float alpha = src[y * rowbytes + (x * bpp) + alpha_channel_idx];
         if((alpha * alpha_scale) >= (alpha_test_threshold * 255))
         {
            ++coverage;
         }
      }
   }

   return (float)coverage / (width * height);
}

void scale_alpha_to_coverage(unsigned char *img,
                             unsigned int width, unsigned int height, int bpp,
                             float desired_coverage,
                             float alpha_test_threshold)
{
   int i;
   unsigned int x, y;
   const int rowbytes = width * bpp;
   const int alpha_channel_idx = 3;
   float min_alpha_scale = 0.0f;
   float max_alpha_scale = 4.0f;
   float alpha_scale = 1.0f;

   if(bpp <= alpha_channel_idx)
   {
      /* No alpha channel */
      return;
   }

   /* Binary search */
   for(i = 0; i < 10; i++)
   {
      float cur_coverage = calc_alpha_test_coverage(img, width, height, bpp, alpha_test_threshold, alpha_scale);

      if(cur_coverage < desired_coverage)
      {
         min_alpha_scale = alpha_scale;
      }
      else if (cur_coverage > desired_coverage)
      {
         max_alpha_scale = alpha_scale;
      }
      else
      {
         break;
      }

      alpha_scale = (min_alpha_scale + max_alpha_scale) / 2;
   }

   /* Scale alpha channel */
   for(y = 0; y < height; ++y)
   {
      for(x = 0; x < width; ++x)
      {
         float new_alpha = img[y * rowbytes + (x * bpp) + alpha_channel_idx] * alpha_scale;
         if(new_alpha > 255.0f)
         {
            new_alpha = 255.0f;
         }

         img[y * rowbytes + (x * bpp) + alpha_channel_idx] = (unsigned char)new_alpha;
      }
   }
}

/******************************************************************************
 * mipmap generation                                                          *
 ******************************************************************************/

int generate_mipmaps(unsigned char *dst, unsigned char *src,
                     unsigned int width, unsigned int height, int bpp,
                     int indexed, int mipmaps, int filter, int wrap,
                     int gc, float gamma,
                     int preserve_alpha_coverage, float alpha_test_threshold)
{
   int i;
   unsigned int sw, sh, dw, dh;
   unsigned char *s, *d;
   mipmapfunc_t mipmap_func = NULL;
   filterfunc_t filter_func = NULL;
   wrapfunc_t wrap_func = NULL;
   float support = 0.0f;
   const int has_alpha = (bpp >= 3);
   float alpha_test_coverage = 1;

   if(indexed || filter == DDS_MIPMAP_FILTER_NEAREST)
   {
      mipmap_func = scale_image_nearest;
   }
   else
   {
      if((filter <= DDS_MIPMAP_FILTER_DEFAULT) ||
         (filter >= DDS_MIPMAP_FILTER_MAX))
         filter = DDS_MIPMAP_FILTER_BOX;

      mipmap_func = scale_image;

      for(i = 0; filters[i].filter != DDS_MIPMAP_FILTER_MAX; ++i)
      {
         if(filter == filters[i].filter)
         {
            filter_func = filters[i].func;
            support = filters[i].support;
            break;
         }
      }
   }

   switch(wrap)
   {
      case DDS_MIPMAP_WRAP_MIRROR: wrap_func = wrap_mirror; break;
      case DDS_MIPMAP_WRAP_REPEAT: wrap_func = wrap_repeat; break;
      case DDS_MIPMAP_WRAP_CLAMP:  wrap_func = wrap_clamp;  break;
      default:                     wrap_func = wrap_clamp;  break;
   }

   if(has_alpha && preserve_alpha_coverage)
   {
      alpha_test_coverage = calc_alpha_test_coverage(src, width, height, bpp,
                                                     alpha_test_threshold,
                                                     1.0f);
   }

   memcpy(dst, src, width * height * bpp);

   s = dst;
   d = dst + (width * height * bpp);

   sw = width;
   sh = height;

   for(i = 1; i < mipmaps; ++i)
   {
      dw = MAX(1, sw >> 1);
      dh = MAX(1, sh >> 1);

      mipmap_func(d, dw, dh, s, sw, sh, bpp, filter_func, support, wrap_func, gc, gamma);

      if(has_alpha && preserve_alpha_coverage)
      {
         scale_alpha_to_coverage(d, dw, dh, bpp, alpha_test_coverage, alpha_test_threshold);
      }

      s = d;
      sw = dw;
      sh = dh;
      d += (dw * dh * bpp);
   }

   return(1);
}

int generate_volume_mipmaps(unsigned char *dst, unsigned char *src,
                            unsigned int width, unsigned int height,
                            unsigned int depth, int bpp, int indexed,
                            int mipmaps, int filter, int wrap,
                            int gc, float gamma)
{
   int i;
   unsigned int sw, sh, sd;
   unsigned int dw, dh, dd;
   unsigned char *s, *d;
   volmipmapfunc_t mipmap_func = NULL;
   filterfunc_t filter_func = NULL;
   wrapfunc_t wrap_func = NULL;
   float support = 0.0f;

   if(indexed || filter == DDS_MIPMAP_FILTER_NEAREST)
   {
      mipmap_func = scale_volume_image_nearest;
   }
   else
   {
      if((filter <= DDS_MIPMAP_FILTER_DEFAULT) ||
         (filter >= DDS_MIPMAP_FILTER_MAX))
         filter = DDS_MIPMAP_FILTER_BOX;

      mipmap_func = scale_volume_image;

      for(i = 0; filters[i].filter != DDS_MIPMAP_FILTER_MAX; ++i)
      {
         if(filter == filters[i].filter)
         {
            filter_func = filters[i].func;
            support = filters[i].support;
            break;
         }
      }
   }

   switch(wrap)
   {
      case DDS_MIPMAP_WRAP_MIRROR: wrap_func = wrap_mirror; break;
      case DDS_MIPMAP_WRAP_REPEAT: wrap_func = wrap_repeat; break;
      case DDS_MIPMAP_WRAP_CLAMP:  wrap_func = wrap_clamp;  break;
      default:                     wrap_func = wrap_clamp;  break;
   }

   memcpy(dst, src, width * height * depth * bpp);

   s = dst;
   d = dst + (width * height * depth * bpp);

   sw = width;
   sh = height;
   sd = depth;

   for(i = 1; i < mipmaps; ++i)
   {
      dw = MAX(1, sw >> 1);
      dh = MAX(1, sh >> 1);
      dd = MAX(1, sd >> 1);

      mipmap_func(d, dw, dh, dd, s, sw, sh, sd, bpp, filter_func, support, wrap_func, gc, gamma);

      s = d;
      sw = dw;
      sh = dh;
      sd = dd;
      d += (dw * dh * dd * bpp);
   }

   return(1);
}