SDL/examples/renderer/07-streaming-textures/streaming-textures.c

/*
 * This example creates an SDL window and renderer, and then draws a streaming
 * texture 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_Texture *texture = NULL;

#define TEXTURE_SIZE 150

#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/streaming-textures", WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &renderer)) {
        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create window/renderer!", SDL_GetError(), NULL);
        return SDL_APP_FAILURE;
    }

    texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_STREAMING, TEXTURE_SIZE, TEXTURE_SIZE);
    if (!texture) {
        SDL_ShowSimpleMessageBox(SDL_MESSAGEBOX_ERROR, "Couldn't create streaming texture!", 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 dst_rect;
    const Uint64 now = SDL_GetTicks();
    SDL_Surface *surface = NULL;

    /* we'll have some color move around 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;

    /* To update a streaming texture, you need to lock it first. This gets you access to the pixels.
       Note that this is considered a _write-only_ operation: the buffer you get from locking
       might not acutally have the existing contents of the texture, and you have to write to every
       locked pixel! */

    /* You can use SDL_LockTexture() to get an array of raw pixels, but we're going to use
       SDL_LockTextureToSurface() here, because it wraps that array in a temporary SDL_Surface,
       letting us use the surface drawing functions instead of lighting up individual pixels. */
    if (SDL_LockTextureToSurface(texture, NULL, &surface)) {
        SDL_Rect r;
        SDL_FillSurfaceRect(surface, NULL, SDL_MapRGB(SDL_GetPixelFormatDetails(surface->format), NULL, 0, 0, 0));  /* make the whole surface black */
        r.w = TEXTURE_SIZE;
        r.h = TEXTURE_SIZE / 10;
        r.x = 0;
        r.y = (int) (((float) (TEXTURE_SIZE - r.h)) * ((scale + 1.0f) / 2.0f));
        SDL_FillSurfaceRect(surface, &r, SDL_MapRGB(SDL_GetPixelFormatDetails(surface->format), NULL, 0, 255, 0));  /* make a strip of the surface green */
        SDL_UnlockTexture(texture);  /* upload the changes (and frees the temporary surface)! */
    }

    /* as you can see from this, rendering draws over whatever was drawn before it. */
    SDL_SetRenderDrawColor(renderer, 66, 66, 66, 255);  /* grey, full alpha */
    SDL_RenderClear(renderer);  /* start with a blank canvas. */

    /* Just draw the static texture a few times. You can think of it like a
       stamp, there isn't a limit to the number of times you can draw with it. */

    /* Center this one. It'll draw the latest version of the texture we drew while it was locked. */
    dst_rect.x = ((float) (WINDOW_WIDTH - TEXTURE_SIZE)) / 2.0f;
    dst_rect.y = ((float) (WINDOW_HEIGHT - TEXTURE_SIZE)) / 2.0f;
    dst_rect.w = dst_rect.h = (float) TEXTURE_SIZE;
    SDL_RenderTexture(renderer, texture, NULL, &dst_rect);

    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_DestroyTexture(texture);
    /* SDL will clean up the window/renderer for us. */
}