you might try

sdl_gfx

zoomSurface()

Zoomes a 32bit or 8bit 'src' surface to newly created 'dst' surface.
'zoomx' and 'zoomy' are scaling factors for width and height. If 'smooth' is 1
then the destination 32bit surface is anti-aliased. If the surface is not 8bit
or 32bit RGBA/ABGR it will be converted into a 32bit RGBA format on the fly.