uses
  SDLImage, ...;

// OpenGL-Textur erstellen
function CreateTexture(SDL_Surface : PSDL_Surface) : Integer;
var tmpInitial : PSDL_Surface;
     Texture    : GluInt;
    MaxAni     : Real;
begin
  // Es ist nicht klar, ob die Funktion erfolgreich durchläuft.
  Result := -1;
  if Assigned(SDL_Surface) then
  begin
    // Für Alphakanal
    tmpInitial := SDL_DisplayFormatAlpha(SDL_Surface);
    SDL_FreeSurface(SDL_Surface);
    // Da der Alphakanal die Farben vertauscht, muss dies über SwapRGB gerade gebogen werden.
    SwapBGR(tmpInitial);

    glGenTextures(1, @Texture);
    glBindTexture(GL_TEXTURE_2D, Texture);
    // Die Größen werden automatisch berechnet. Sonst wären nur Potenzen von 2 möglich (16x16, 32x32, usw.).
    if tmpInitial.format.BytesPerPixel > 3 then
      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tmpInitial^.w, tmpInitial^.h, 0, GL_RGBA, GL_UNSIGNED_BYTE, tmpInitial^.pixels)
    else
      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, tmpInitial^.w, tmpInitial^.h, 0, GL_RGB, GL_UNSIGNED_BYTE, tmpInitial^.pixels);
    // Textureigenschaften setzen
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR);
    if IsExtensionSupported('GL_EXT_texture_filter_anisotropic') then
    begin
      glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, @MaxAni);
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, MaxAni/2);
    end;
    glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);
    glGenerateMipmap(GL_TEXTURE_2D);
    // Mipmaps generieren
    if tmpInitial.format.BytesPerPixel > 3 then
      gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGBA, tmpInitial^.w, tmpInitial^.h, GL_RGBA, GL_UNSIGNED_BYTE, tmpInitial^.pixels)
    else
      gluBuild2DMipmaps(GL_TEXTURE_2D, GL_RGB, tmpInitial^.w, tmpInitial^.h, GL_RGB, GL_UNSIGNED_BYTE, tmpInitial^.pixels);
    // Freigabe
    SDL_FreeSurface(tmpInitial);
    // Rückgabe
    Result := Texture;
  end;
end;

// Textur aus Datei laden und mit definierten Index in Texturarray schreiben
function LoadTexture(Filename : String; aId : Integer) : Boolean;
begin
  Result := False;
  if FileExists(Filename) then
  begin
    SetLength(Tex, High(Tex)+2);
    with Tex[High(Tex)] do
    begin
      Id     := Succ(aId);
      Textur := CreateTexture(IMG_Load(PChar(Filename)));
    end;
    Result := True;
  end;
end;

// Farben vertauschen
procedure SwapBGR(SDLSurface : PSDL_Surface);
var x, y           : Integer;
    p              : UInt32;
    pR, pG, pB, pA : PUInt8;
    r, g, b, a     : UInt8;
begin
  for y := 0 to Pred(SDLSurface.h) do
    for x := 0 to Pred(SDLSurface.w) do
    begin
      p := SDL_GetPixel(SDLSurface, x, y);

      pR := @r;
      pG := @g;
      pB := @b;
      pA := @a;

      SDL_GetRGBA(p, SDLSurface.format, pR, pG, pB, pA);
      p := SDL_MapRGBA(SDLSurface.format, b, g, r, a);

      SDL_PutPixel(SDLSurface, x, y, p);
    end;
end;

function LoadTexture(name : String) : GLuint;
var surface : PSDL_Surface;
    texture : GLuint;
begin
  surface:=IMG_Load(@name[1]);
  glGenTextures(1,@texture);
  glBindTexture(GL_TEXTURE_2D,texture);
  glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_LINEAR); 
  gluBuild2DMipmaps(GL_TEXTURE_2D,4,surface^.w,surface^.h,GL_RGBA,GL_UNSIGNED_BYTE,surface^.pixels);
  SDL_FreeSurface(surface);
  exit(texture);
end;

function LoadTexture(name : String) : GLuint;
var surface : PSDL_Surface;
    texture : GLuint;
    buffer  : pchar;
begin
  surface:=IMG_Load(@name[1]);
  if surface=nil then
  begin
    buffer:= SDL_GetError;
    writeln(buffer);
  end;
  glGenTextures(1,@texture);
  glBindTexture(GL_TEXTURE_2D,texture);
  glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR_MIPMAP_LINEAR); 
  gluBuild2DMipmaps(GL_TEXTURE_2D,4,surface^.w,surface^.h,GL_RGBA,GL_UNSIGNED_BYTE,surface^.pixels);
  SDL_FreeSurface(surface);
  exit(texture);
end;

  glEnable(GL_BLEND);
  glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);