(src/sdl_stretch.h)
#include <SDL_stretch.h>
extern DECLSPEC int SDL_StretchSurface_23(SDL_Surface *src, SDL_Rect *srcrect, SDL_Surface *dst, SDL_Rect *dstrect);
The SDL_StretchSurface_23 function will stretch to 150%. This is not only a fast function but it is also safe to call from multiple threads. If the srcrect is given then only that rect is copied. Otherwise the full src surface is copied to the full dst surface. The dstrect is ignored.