SDL/examples/renderer/01-clear/clear.c

/*
 * This example code creates an SDL window and renderer, and then clears the
 * window to a different color every frame, so you'll effectively get a window
 * that's smoothly fading between colors.
 *
 * 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;

/* 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/clear", 640, 480, 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)
{
    const double now = ((double)SDL_GetTicks()) / 1000.0;  /* convert from milliseconds to seconds. */
    /* choose the color for the frame we will draw. The sine wave trick makes it fade between colors smoothly. */
    const float red = (float) (0.5 + 0.5 * SDL_sin(now));
    const float green = (float) (0.5 + 0.5 * SDL_sin(now + SDL_PI_D * 2 / 3));
    const float blue = (float) (0.5 + 0.5 * SDL_sin(now + SDL_PI_D * 4 / 3));
    SDL_SetRenderDrawColorFloat(renderer, red, green, blue, 1.0f);  /* new color, full alpha. */

    /* clear the window to the draw color. */
    SDL_RenderClear(renderer);

    /* put the newly-cleared rendering on the screen. */
    SDL_RenderPresent(renderer);

    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. */
}