SDL2 Animation in ANSI C

sdlanim.c

// to compile and run: gcc -o Mikas t.c -lsdl2 && ./Mikas
//
#include <stdio.h>
#include <stdbool.h>
#include <SDL2/SDL.h>
#include <stdlib.h>

#define WINDOW_WIDTH 800
#define WINDOW_HEIGHT 600
#define RECT_SIZE 64
#define FPS 90

#define MIN(a,b) (((a)<(b))?(a):(b))
#define MAX(a,b) (((a)>(b))?(a):(b))

/*
 * Produces a random int x, min <= x <= max
 * following a uniform distribution
 */
int randomInt(int min, int max) {
  return min + rand() % abs(max - min + 1);
}

int clamp(int n, int a, int b) {
  return MAX(a, MIN(n, b));
}

int main(int argc, char **argv) {
  SDL_Window *window;
  SDL_Renderer *renderer;

  const Uint8 *keyboard;

  int renderW;
  int renderH;
  int frame = 0;
  
  bool quit_flag = false;
  
  if (SDL_Init(SDL_INIT_VIDEO) < 0) {
    SDL_Log("Unable to initialize SDL: %s", SDL_GetError());
    return -1;
  }

  if ((window = SDL_CreateWindow("Mikas Play", 0, 0, WINDOW_WIDTH, WINDOW_HEIGHT, 0 /* SDL_WINDOW_FULLSCREEN */ )) == 0)
    goto do_exit;

  if ((renderer = SDL_CreateRenderer(window, -1,
				     SDL_RENDERER_ACCELERATED |
				     SDL_RENDERER_PRESENTVSYNC)) == 0)
    goto do_exit;

  SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "2");
  
  SDL_DisplayMode mode;
  int res = SDL_GetCurrentDisplayMode(2, &mode);
  int real_fps = mode.refresh_rate !=0 ? mode.refresh_rate : 60;
  printf("Reported FPS: %d\n", mode.refresh_rate);
  
  /* Come up with a random color */
  int r = 128; //randomInt(50, 255);
  int g = 128; //randomInt(50, 255);
  int b = 128; //randomInt(50, 255);

  SDL_RenderGetLogicalSize(renderer, &renderW, &renderH);
  
  keyboard = SDL_GetKeyboardState(NULL);

  while (!quit_flag) {
    frame++;
    
    SDL_Event event;
    while (SDL_PollEvent(&event)) {
      
      if (event.type == SDL_QUIT) {
	quit_flag = true;
      }
      else if (event.type == SDL_KEYDOWN && keyboard[SDL_SCANCODE_Q] != 0) {
	quit_flag = true;
      }
    }

    SDL_SetRenderDrawColor(renderer, 0x18, 0x18, 0x18, 0xff);
    SDL_RenderClear(renderer);

    /*  Fill the rectangle in the color */
    for(int i=15; i > 0; i-=1) {
      SDL_Rect rect;
      rect.w = RECT_SIZE;
      rect.h = RECT_SIZE;
      rect.x = (WINDOW_WIDTH  / 2 - 50) * sin(1.0 * 3.14 * (frame-i*4) / FPS) + (WINDOW_WIDTH  - RECT_SIZE) / 2;
      rect.y = (WINDOW_HEIGHT / 2 - 50) * cos(1.2 * 3.14 * (frame-i*4) / FPS) + (WINDOW_HEIGHT - RECT_SIZE) / 2;
      SDL_SetRenderDrawColor(renderer,
			     clamp(r - i*10, 0, 255),
			     clamp(g - i*10, 0, 255),
			     clamp(b - i*10, 0, 255),
			     clamp(255-i*20, 0, 255));
      SDL_RenderFillRect(renderer, &rect);
    }

    r = clamp(r + randomInt(-1, 1), 0, 255);
    g = clamp(g + randomInt(-1, 1), 0, 255);
    b = clamp(b + randomInt(-1, 1), 0, 255);

    SDL_RenderPresent(renderer);
    SDL_Delay(1000 / real_fps);
  }
  
 do_exit:
  if (renderer != NULL) SDL_DestroyRenderer(renderer);
  if (window != NULL) SDL_DestroyWindow(window);
  SDL_Quit();
  
  return 0;
}