dds_opengl_loader.c

#define FOURCC(s)  (((uint32)s[0]<<0) | ((uint32)s[1]<<8) | ((uint32)s[2]<<16) | ((uint32)s[3]<<24))

// this is not the public function, see following two functions after this one
static GLuint load_dds_bc_only_raw(GLuint tex, int slice, int total_slices, char *filename)
{
   int target = slice < 0 ? GL_TEXTURE_2D : GL_TEXTURE_2D_ARRAY, i, mips;
   GLenum fmt_for_bc[8] = { 0, 0x83F0, 0x83F2, 0x83F3, 0x8DBB, 0x8DBD, 0x8E8E, 0x8E8F }; 
   int bytes_per_4x4block[8] = { 0, 8,16,16,8,16,16,16 };
   uint32 width,height,flags,size,fourcc,depth,fflags,caps,caps2,dim=0;
   int len, bc=0, fmt=1, intfmt;
   uint32 *data = (uint32 *) stb_file(filename, &len);
   char *pixels;
   if (data == 0 || len < 128) goto fail; // file too small or non-existant
   if (data[0] != 0x20534444) goto fail; // dwMagic
   if (data[1] != 124       ) goto fail; // dwSize
   flags = data[2];
   width = data[3];
   height = data[4];
   if (width > 65536 || height > 65536) goto fail; // probably corrupted
   if ((width>>2) * (height>>2) > (1u<<24)) goto fail; // total pixels > 2^28, probably corrupted
   size = data[5]; // dwPitchOrLinearSize
   depth = data[6];
   if (flags & 0x20000) //  DDSD_MIPMAPCOUNT
      mips = (int) data[7];
   else
      mips = 1;
   // data[8]..data[18] dwReserved
   if (data[19] != 32) goto fail; // dwSize
   fflags = data[20]; // dwFlags
   if (fflags & 0x40) goto fail; // uncompressed
   if (!(fflags & 0x4)) goto fail; // no FOURCC
   fourcc = data[21];
   // data[21] dwRGBBitCount
   // data[22..25] R/G/B/A mask
   caps = data[26];
   caps2 = data[27];
   pixels = (char*) &data[32];
   if (fourcc == FOURCC("DXT1")) bc=1;
   if (fourcc == FOURCC("DXT5")) bc=3;
   if (fourcc == FOURCC("ATI2")) bc=5;
   if (fourcc == FOURCC("BC5S")) bc=5, fmt=3; // SNORM
   if (fourcc == FOURCC("DX10")) {
      uint32 dxgifmt;
      if (len < 148) goto fail;
      dxgifmt = data[32];
      if (dxgifmt >= 70 && dxgifmt <= 84) {
         bc = 1 + (dxgifmt-70)/3;
         fmt = (dxgifmt-70)%3; // TYPELESS, UNORM, UNORM_SRGB
      } else if (dxgifmt >= 94 && dxgifmt <= 99) {
         bc = 6 + (dxgifmt-94)/3;
         fmt = (dxgifmt-70)%3; // bc6 is actually different meaning for fmt=1,2
      } else
         goto fail; // unhandled format, we only do BC1..BC7
      dim = data[33];
      pixels = (char*) &data[37];
   }
   if (bc == 0) goto fail;
   // @TODO mipmaps, arrays, cubemaps -- maybe use ktx for those!

   if (size != ((width+3)/4)*((height+3)/4)*bytes_per_4x4block[bc]) goto fail; // size isn't correct
   if (pixels - (char*)data + size > (unsigned) len) goto fail; // size goes past EOF
   intfmt = fmt_for_bc[bc];
   if (bc == 4 && fmt == 3) intfmt = 0x8DBC; // GL_COMPRESSED_SIGNED_RED_RGTC1
   if (bc == 5 && fmt == 3) intfmt = 0x8DBE; // GL_COMPRESSED_SIGNED_RG_RGTC2

   if (tex == 0) {
      assert(slice >= 0);
      glGenTextures(1, &tex);
      glBindTexture(target, tex);
      for (i=0; i < mips; ++i)
         glTexImage3D(target, i, intfmt, width>>i,height>>i,total_slices,0,GL_RGB,GL_UNSIGNED_BYTE,0);
      if (mips)
         glTexParameteri(target, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
      else
         glTexParameteri(target, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
      glTexParameteri(target, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
   }

   glBindTexture(target, tex);

   for (i=0; i < mips; ++i) {
      if (pixels - (char*)data + size > (unsigned) len) goto fail; // size goes past EOF
      if (target == GL_TEXTURE_2D)
         glCompressedTexImage2D(target, i, intfmt, width, height, 0, size, pixels);
      else
         glCompressedTexSubImage3D(target, i, 0,0,slice,width,height,1,intfmt,size,pixels);
      pixels += size;
      width = width>>1;
      height = height>>1;
      size = ((width+3)/4)*((height+3)/4)*bytes_per_4x4block[bc];
   }

   glBindTexture(target, 0);
   free(data);
   return tex;
fail:
   free(data);
   return tex;
}

// caller has to set GL_LINEAR_MIPMAP_LINEAR if there are mipmaps
static GLuint load_dds_bc_only(char *filename)
{
   GLuint tex;
   glGenTextures(1, &tex);
   glBindTexture(GL_TEXTURE_2D, tex);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
   return load_dds_bc_only_raw(tex,-1,0, filename);
}

static GLuint load_dds_bc_only_array(char *filename, GLuint tex, int total_slices, int slice)
{
   return load_dds_bc_only_raw(tex, slice, total_slices, filename);
}