private
   data: array of byte; // RGBARGBARGBA
   width: word;
   height: word;
   procedure load8888(f: string);     // mode = 1
   procedure load888(f: string);      // mode = 2
   procedure load4444(f: string);     // mode = 3
   procedure load5551(f: string);     // mode = 4
   procedure save8888(f: string);
   procedure save888(f: string);
   procedure save4444(f: string);
   procedure save5551(f: string);
 public
   procedure LoadBitMap(bmp, alpha: string);
   procedure LoadTexture(file_name: string; var texture: GLuint);
   procedure SaveTexture(file_name: string; mode: byte = 1);
 end;

procedure tGTexture.LoadTexture(file_name: string; var texture: GLuint);
var
 f: file of byte;
 mode: byte;
 pData: Pointer;
begin
 AssignFile(f, file_name);
 Reset(f);
 Read(f, mode);
 CloseFile(f);
 case mode of
   1: load8888(file_name);
   2: load888(file_name);
   3: load4444(file_name);
   4: load5551(file_name);
 end;

 GetMem(pData, length(data));
 move(data, pData^, length(data));

 glGenTextures(1, Texture);
 glBindTexture(GL_TEXTURE_2D, Texture);
 glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);  {Texture blends with object background}

 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); { only first two can be used }
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); { all of the above can be used }

 gluBuild2DMipmaps(GL_TEXTURE_2D, 4, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pData);
end;