main.c

#define SDL_MAIN_USE_CALLBACKS

#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>

static SDL_Window *window = NULL;
static SDL_Renderer *renderer = NULL;

static SDL_FRect mouseposrect;

SDL_AppResult SDL_AppIterate(void *appstate)
{
    Uint8 r;

    /* fade between shades of red every 3 seconds, from 0 to 255. */
    r = (Uint8) ((((float) (SDL_GetTicks() % 3000)) / 3000.0f) * 255.0f);
    SDL_SetRenderDrawColor(renderer, r, 0, 0, 255);

    /* you have to draw the whole window every frame. Clearing it makes sure the whole thing is sane. */
    SDL_RenderClear(renderer);  /* clear whole window to that fade color. */

    /* set the color to white */
    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);

    /* draw a square where the mouse cursor currently is. */
    SDL_RenderFillRect(renderer, &mouseposrect);

    /* put everything we drew to the screen. */
    SDL_RenderPresent(renderer);

    return SDL_APP_CONTINUE;
}

SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event)
{
    switch (event->type) {
        case SDL_EVENT_QUIT:  /* triggers on last window close and other things. End the program. */
            return SDL_APP_SUCCESS;

        case SDL_EVENT_KEY_DOWN:  /* quit if user hits ESC key */
            if (event->key.scancode == SDL_SCANCODE_ESCAPE) {
                return SDL_APP_SUCCESS;
            }
            break;

        case SDL_EVENT_MOUSE_MOTION:  /* keep track of the latest mouse position */
            /* center the square where the mouse is */
            mouseposrect.x = event->motion.x - (mouseposrect.w / 2);
            mouseposrect.y = event->motion.y - (mouseposrect.h / 2);
            break;
    }
    return SDL_APP_CONTINUE;
}

SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
{
    SDL_SetAppMetadata("SDL Hello World Example", "1.0", "com.example.sdl-hello-world");

    if (!SDL_Init(SDL_INIT_VIDEO)) {
        SDL_Log("SDL_Init(SDL_INIT_VIDEO) failed: %s", SDL_GetError());
        return SDL_APP_FAILURE;
    }

    if (!SDL_CreateWindowAndRenderer("Hello SDL", 640, 480, SDL_WINDOW_RESIZABLE, &window, &renderer)) {
        SDL_Log("SDL_CreateWindowAndRenderer() failed: %s", SDL_GetError());
        return SDL_APP_FAILURE;
    }

    mouseposrect.x = mouseposrect.y = -1000;  /* -1000 so it's offscreen at start */
    mouseposrect.w = mouseposrect.h = 50;

    return SDL_APP_CONTINUE;
}

void SDL_AppQuit(void *appstate, SDL_AppResult result)
{
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
}