kaizen/examples/renderer/04-points/points.c

/*
 * This example creates an SDL window and renderer, and then draws some points
 * to it every frame.
 *
 * This code is public domain. Feel free to use it for any purpose!
 */

#define SDL_MAIN_USE_CALLBACKS 1  /* use the callbacks instead of main() */
#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>

/* We will use this renderer to draw into this window every frame. */
static SDL_Window *window = NULL;
static SDL_Renderer *renderer = NULL;
static Uint64 last_time = 0;

#define WINDOW_WIDTH 640
#define WINDOW_HEIGHT 480

#define NUM_POINTS 500
#define MIN_PIXELS_PER_SECOND 30  /* move at least this many pixels per second. */
#define MAX_PIXELS_PER_SECOND 60  /* move this many pixels per second at most. */

/* (track everything as parallel arrays instead of a array of structs,
   so we can pass the coordinates to the renderer in a single function call.) */

/* Points are plotted as a set of X and Y coordinates.
   (0, 0) is the top left of the window, and larger numbers go down
   and to the right. This isn't how geometry works, but this is pretty
   standard in 2D graphics. */
static SDL_FPoint points[NUM_POINTS];
static float point_speeds[NUM_POINTS];

/* This function runs once at startup. */
SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
{
    int i;

    if (!SDL_Init(SDL_INIT_VIDEO)) {
        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't initialize SDL!", SDL_GetError(), NULL);
        return SDL_APP_FAILURE;
    }

    if (!SDL_CreateWindowAndRenderer("examples/renderer/points", WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &renderer)) {
        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create window/renderer!", SDL_GetError(), NULL);
        return SDL_APP_FAILURE;
    }

    SDL_srand(0);  /* seed the random number generator */

    /* set up the data for a bunch of points. */
    for (i = 0; i < SDL_arraysize(points); i++) {
        points[i].x = SDL_randf() * ((float) WINDOW_WIDTH);
        points[i].y = SDL_randf() * ((float) WINDOW_HEIGHT);
        point_speeds[i] = MIN_PIXELS_PER_SECOND + (SDL_randf() * (MAX_PIXELS_PER_SECOND - MIN_PIXELS_PER_SECOND));
    }

    last_time = SDL_GetTicks();

    return SDL_APP_CONTINUE;  /* carry on with the program! */
}

/* This function runs when a new event (mouse input, keypresses, etc) occurs. */
SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event)
{
    if (event->type == SDL_EVENT_QUIT) {
        return SDL_APP_SUCCESS;  /* end the program, reporting success to the OS. */
    }
    return SDL_APP_CONTINUE;  /* carry on with the program! */
}

/* This function runs once per frame, and is the heart of the program. */
SDL_AppResult SDL_AppIterate(void *appstate)
{
    const Uint64 now = SDL_GetTicks();
    const float elapsed = ((float) (now - last_time)) / 1000.0f;  /* seconds since last iteration */
    int i;

    /* let's move all our points a little for a new frame. */
    for (i = 0; i < SDL_arraysize(points); i++) {
        const float distance = elapsed * point_speeds[i];
        points[i].x += distance;
        points[i].y += distance;
        if ((points[i].x >= WINDOW_WIDTH) || (points[i].y >= WINDOW_HEIGHT)) {
            /* off the screen; restart it elsewhere! */
            if (SDL_rand(2)) {
                points[i].x = SDL_randf() * ((float) WINDOW_WIDTH);
                points[i].y = 0.0f;
            } else {
                points[i].x = 0.0f;
                points[i].y = SDL_randf() * ((float) WINDOW_HEIGHT);
            }
            point_speeds[i] = MIN_PIXELS_PER_SECOND + (SDL_randf() * (MAX_PIXELS_PER_SECOND - MIN_PIXELS_PER_SECOND));
        }
    }

    last_time = now;

    /* as you can see from this, rendering draws over whatever was drawn before it. */
    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);  /* black, full alpha */
    SDL_RenderClear(renderer);  /* start with a blank canvas. */
    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);  /* white, full alpha */
    SDL_RenderPoints(renderer, points, SDL_arraysize(points));  /* draw all the points! */

    /* You can also draw single points with SDL_RenderPoint(), but it's
       cheaper (sometimes significantly so) to do them all at once. */

    SDL_RenderPresent(renderer);  /* put it all on the screen! */

    return SDL_APP_CONTINUE;  /* carry on with the program! */
}

/* This function runs once at shutdown. */
void SDL_AppQuit(void *appstate)
{
    /* SDL will clean up the window/renderer for us. */
}