[SDL] Blitting OpenGL texture.

[Ryan Williams]

Hi, I'm using SDL and OpenGL to make a 2D game. I have my sprites as 1 
long PNG file with all the frames of animation, what I want to do is 
blit the frame I want into an opengl texture. This is the code I'm using:


   SDL_Surface* m_gSprites(IMG_Load("sprites.png"));
   glGenTextures(1, &m_nTextureID);
   glBindTexture(GL_TEXTURE_2D, m_nTextureID);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

   SDL_Rect tSrcRect;
   SDL_Rect tDesRect;
   tSrcRect.x = 0;
   tSrcRect.y = m_iSize*m_iFrame;
   tSrcRect.w = m_iSize;
   tSrcRect.h = m_iSize;
   tDesRect.x = 0;
   tDesRect.y = 0;
     SDL_Surface* tSurface(SDL_CreateRGBSurface(SDL_SWSURFACE, m_iSize, 
m_iSize, 32, rmask, gmask, bmask, amask));
   SDL_BlitSurface(m_gSprites, &tSrcRect, tSurface, &tDesRect);
   glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_iSize, m_iSize, 0, GL_RGBA, 
GL_UNSIGNED_BYTE, tSurface->pixels);

This results in a totally empty texture, but if i add this before blitting:

   SDL_FillRect(tSurface, NULL, 0x55ffffff);

I can see it's copied the texture fine but is semi-transparent like the 
rectangle I filled it with, it seems to be using the alpha from the 
destination surface. Am I missing something I need to apply to the 
destination surface before blitting?

Thanks

-- 
Ryan Williams
http://ryanwilliams.org