kaizen/examples/renderer/05-rectangles/rectangles.c

/*
 * This example creates an SDL window and renderer, and then draws some
 * rectangles 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;

#define WINDOW_WIDTH 640
#define WINDOW_HEIGHT 480

/* This function runs once at startup. */
SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
{
    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/rectangles", WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &renderer)) {
        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create window/renderer!", SDL_GetError(), NULL);
        return SDL_APP_FAILURE;
    }

    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)
{
    SDL_FRect rects[16];
    const Uint64 now = SDL_GetTicks();
    int i;

    /* we'll have the rectangles grow and shrink over a few seconds. */
    const float direction = ((now % 2000) >= 1000) ? 1.0f : -1.0f;
    const float scale = ((float) (((int) (now % 1000)) - 500) / 500.0f) * direction;

    /* 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. */

    /* Rectangles are comprised of set of X and Y coordinates, plus width and
       height. (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. */

    /* Let's draw a single rectangle (square, really). */
    rects[0].x = rects[0].y = 100;
    rects[0].w = rects[0].h = 100 + (100 * scale);
    SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);  /* red, full alpha */
    SDL_RenderRect(renderer, &rects[0]);

    /* Now let's draw several rectangles with one function call. */
    for (i = 0; i < 3; i++) {
        const float size = (i+1) * 50.0f;
        rects[i].w = rects[i].h = size + (size * scale);
        rects[i].x = (WINDOW_WIDTH - rects[i].w) / 2;  /* center it. */
        rects[i].y = (WINDOW_HEIGHT - rects[i].h) / 2;  /* center it. */
    }
    SDL_SetRenderDrawColor(renderer, 0, 255, 0, 255);  /* green, full alpha */
    SDL_RenderRects(renderer, rects, 3);  /* draw three rectangles at once */

    /* those were rectangle _outlines_, really. You can also draw _filled_ rectangles! */
    rects[0].x = 400;
    rects[0].y = 50;
    rects[0].w = 100 + (100 * scale);
    rects[0].h = 50 + (50 * scale);
    SDL_SetRenderDrawColor(renderer, 0, 0, 255, 255);  /* blue, full alpha */
    SDL_RenderFillRect(renderer, &rects[0]);

    /* ...and also fill a bunch of rectangles at once... */
    for (i = 0; i < SDL_arraysize(rects); i++) {
        const float w = (float) (WINDOW_WIDTH / SDL_arraysize(rects));
        const float h = i * 8.0f;
        rects[i].x = i * w;
        rects[i].y = WINDOW_HEIGHT - h;
        rects[i].w = w;
        rects[i].h = h;
    }
    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);  /* white, full alpha */
    SDL_RenderFillRects(renderer, rects, SDL_arraysize(rects));

    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. */
}