code/bouncing-ball/bouncing.c

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#include <SDL2/SDL.h>
#define WIDTH 800
#define HEIGHT 600

typedef struct {
        int x;
        int y;
} vec2d;

typedef struct {
        vec2d pos;
        vec2d speed;
        vec2d acc;
        int size;
} ball;

vec2d add_vec2d(vec2d a, vec2d b){
        vec2d c = { .x = 0, .y = 0 };
        c.x = a.x + b.x;
        c.y = a.y + b.y;

        return c;
}

void bounce_ball(ball *b, int x, int y) {
        if (b->pos.x >= x || b->pos.x < 0) 
                b->speed.x *= -1;
        if (b->pos.y >= y || b->pos.y < 0)
                b->speed.y *= -1;
}


void update_ball(ball *b) {
        b->pos = add_vec2d(b->pos, b->speed);
        b->speed = add_vec2d(b->speed, b->acc);
        bounce_ball(b, WIDTH, HEIGHT);
}

void update(SDL_Renderer *ren, unsigned int ticks, ball *b){
        SDL_SetRenderDrawColor(ren, 128, 128, 128, 255);
        SDL_RenderClear(ren);


        SDL_SetRenderDrawColor(ren, 255, 0, 0, 255);
        SDL_Rect ballrect = {
                .x = b->pos.x,
                .y = b->pos.y,
                .w = b->size / 2,
                .h = b->size / 2
        };

        SDL_RenderFillRect(ren, &ballrect);
        update_ball(b);

}


int main(int argc, char** argv) {
        if (SDL_Init(SDL_INIT_VIDEO) != 0) {
                fprintf(stderr, "Error initializing SDL");
                return 1;
        }
        ball b;
        b.pos.x = 100;
        b.pos.y = 100;
        b.speed.x = 5;
        b.speed.y = 1;
        b.acc.x = 0;
        b.acc.y = 0;
        b.size = 30;

        SDL_Window *win = SDL_CreateWindow("New Window", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, WIDTH, HEIGHT, SDL_WINDOW_OPENGL);
        SDL_Renderer *ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
        bool running = true;
        SDL_Event ev;
        unsigned int ticks = 0;
        while (running) {
                while (SDL_PollEvent(&ev)){
                        ticks = SDL_GetTicks();
                        if (ev.type == SDL_QUIT){
                                running = false;
                                break;
                        }
                        unsigned int newticks = SDL_GetTicks();
                        ticks = (newticks - ticks) / 1000;
                }

                update(ren, ticks, &b);
                SDL_RenderPresent(ren);

        }
        SDL_DestroyRenderer(ren);
        SDL_DestroyWindow(win);
        SDL_Quit();

        return (0);
}