#include <SDL2/SDL.h>

// Initialize
SDL_Init(SDL_INIT_VIDEO);
SDL_Window *window;
SDL_Renderer *renderer;
SDL_CreateWindowAndRenderer(300, 300, 0, &window, &renderer);

// Repeat this to update image
SDL_SetRenderDrawColor(renderer, 0x00, 0x80, 0x00, 0xFF);
SDL_Rect rect1 = {.x = 10, .y = 10, .w = 150, .h = 100};
SDL_RenderFillRect(renderer, &rect1);
SDL_SetRenderDrawColor(renderer, 0x80, 0x80, 0x00, 0xFF);
SDL_Rect rect2 = {.x = 20, .y = 20, .w = 100, .h = 50};
SDL_RenderFillRect(renderer, &rect2);
SDL_RenderPresent(renderer);

Waiting for compiler to load... (~55 MiB)