// Src = a precached surface, dest = surf_game

DestR.x = Origin.X - g_pApp->m_pGame->m_nCameraEnt.X;
DestR.y = Origin.Y - g_pApp->m_pGame->m_nCameraEnt.Y;

SDL_BlitSurface(Src, &SrcR, Dest, &DestR);