SDL_FillRect (3) Linux Manual Page
SDL_FillRect – This function performs a fast fill of the given rectangle with some color
Synopsis
#include "SDL.h" int SDL_FillRect(SDL_Surface *dst, SDL_Rect *dstrect, Uint32 color);
Description
This function performs a fast fill of the given rectangle with color. If dstrect is NULL, the whole surface will be filled with color.The color should be a pixel of the format used by the surface, and can be generated by the SDL_MapRGB or SDL_MapRGBA functions. If the color value contains an alpha value then the destination is simply "filled" with that alpha information, no blending takes place.
If there is a clip rectangle set on the destination (set via SDL_SetClipRect) then this function will clip based on the intersection of the clip rectangle and the dstrect rectangle and the dstrect rectangle will be modified to represent the area actually filled.