examples/renderer/02-primitives/primitives.c

/*
 * This example creates an SDL window and renderer, and then draws some lines,
 * rectangles and 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 SDL_FPoint points[500];

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

    SDL_SetAppMetadata("Example Renderer Primitives", "1.0", "com.example.renderer-primitives");

    if (!SDL_Init(SDL_INIT_VIDEO)) {
        SDL_Log("Couldn't initialize SDL: %s", SDL_GetError());
        return SDL_APP_FAILURE;
    }

    if (!SDL_CreateWindowAndRenderer("examples/renderer/primitives", 640, 480, SDL_WINDOW_RESIZABLE, &window, &renderer)) {
        SDL_Log("Couldn't create window/renderer: %s", SDL_GetError());
        return SDL_APP_FAILURE;
    }
    SDL_SetRenderLogicalPresentation(renderer, 640, 480, SDL_LOGICAL_PRESENTATION_LETTERBOX);

    /* set up some random points */
    for (i = 0; i < SDL_arraysize(points); i++) {
        points[i].x = (SDL_randf() * 440.0f) + 100.0f;
        points[i].y = (SDL_randf() * 280.0f) + 100.0f;
    }

    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 rect;

    /* as you can see from this, rendering draws over whatever was drawn before it. */
    SDL_SetRenderDrawColor(renderer, 33, 33, 33, SDL_ALPHA_OPAQUE);  /* dark gray, full alpha */
    SDL_RenderClear(renderer);  /* start with a blank canvas. */

    /* draw a filled rectangle in the middle of the canvas. */
    SDL_SetRenderDrawColor(renderer, 0, 0, 255, SDL_ALPHA_OPAQUE);  /* blue, full alpha */
    rect.x = rect.y = 100;
    rect.w = 440;
    rect.h = 280;
    SDL_RenderFillRect(renderer, &rect);

    /* draw some points across the canvas. */
    SDL_SetRenderDrawColor(renderer, 255, 0, 0, SDL_ALPHA_OPAQUE);  /* red, full alpha */
    SDL_RenderPoints(renderer, points, SDL_arraysize(points));

    /* draw a unfilled rectangle in-set a little bit. */
    SDL_SetRenderDrawColor(renderer, 0, 255, 0, SDL_ALPHA_OPAQUE);  /* green, full alpha */
    rect.x += 30;
    rect.y += 30;
    rect.w -= 60;
    rect.h -= 60;
    SDL_RenderRect(renderer, &rect);

    /* draw two lines in an X across the whole canvas. */
    SDL_SetRenderDrawColor(renderer, 255, 255, 0, SDL_ALPHA_OPAQUE);  /* yellow, full alpha */
    SDL_RenderLine(renderer, 0, 0, 640, 480);
    SDL_RenderLine(renderer, 0, 480, 640, 0);

    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_AppResult result)
{
    /* SDL will clean up the window/renderer for us. */
}