Question

How to draw a fiiled rectangle that grows and shrinks constantly using SDL3 in Win32 C++

Answer 1

#include <SDL3/SDL.h>

#if _WIN32 // PLATFORM_WINDOWS 

#define WINDOW_WIDTH 800
#define WINDOW_HEIGHT 600

#define WIN32_LEAN_AND_MEAN // Exclude rarely-used stuff from Windows headers
#include <windows.h>

int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
    _In_opt_ HINSTANCE hPrevInstance,
    _In_ LPWSTR lpCmdLine,
    _In_ int nCmdShow) {

    if (!SDL_Init(SDL_INIT_VIDEO)) {
        // SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't initialize SDL: %s", SDL_GetError());
        MessageBoxA(0, SDL_GetError(), "Couldn't initialize SDL", MB_OK);
        return 3;
    }

    SDL_Window* window;
    SDL_Renderer* renderer;
    if (!SDL_CreateWindowAndRenderer("SDL3 Draw a filled rectangle that grows and shrinks constantly", WINDOW_WIDTH, WINDOW_HEIGHT, SDL_WINDOW_RESIZABLE, &window, &renderer)) {
        // SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't create window and renderer: %s", SDL_GetError());
        MessageBoxA(0, SDL_GetError(), "Couldn't create window and renderer", MB_OK);
        return 3;
    }

    SDL_Event event;

    while (1) {
        SDL_PollEvent(&event);
        if (event.type == SDL_EVENT_QUIT) {
            break;
        }

        SDL_FRect rect;
        const Uint64 now = SDL_GetTicks();

        // a rectangle that grows and shrinks constantly 
        const float direction = ((now % 2000) >= 1000) ? 1.0f : -1.0f;
        const float scale = ((float)(((int)(now % 1000)) - 500) / 500.0f) * direction;

        // clear the windows with black color
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);  
        SDL_RenderClear(renderer); // start with a blank canvas

        // draw a single filled rectangle
        rect.x = 200;
        rect.y = 100;
        rect.w = 200 + (200 * scale);
        rect.h = 100 + (100 * scale);
        SDL_SetRenderDrawColor(renderer, 0, 255, 0, SDL_ALPHA_OPAQUE);  // green
        SDL_RenderFillRect(renderer, &rect);

        SDL_RenderPresent(renderer); // put it all on the screen
    }

    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);

    SDL_Quit();

    return 0;
}

#endif

 

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