Question

How to draw random points moving across the screen using SDL3 in Win32 C++

Answer 1

#include <SDL3/SDL.h>

#if _WIN32 // PLATFORM_WINDOWS 

#define WINDOW_WIDTH 800
#define WINDOW_HEIGHT 600

#define TOTAL_POINTS 550
#define MIN_PIXELS_PER_SECOND 30 // move min 30 pixels per second
#define MAX_PIXELS_PER_SECOND 60 // move max 60 pixels per second

#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 random points moving across the screen", 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;
    }

    /*
        typedef struct SDL_FPoint // X and Y coordinates
        {
            // top left of the window
            float x;
            float y;
        } SDL_FPoint;
    */

    SDL_FPoint points[TOTAL_POINTS];
    float point_speeds[TOTAL_POINTS];

    // Set up random x, y and distance(speed) for all points
    for (int i = 0; i < SDL_arraysize(points); i++) {
        points[i].x = SDL_randf() * ((float)WINDOW_WIDTH);
        points[i].y = SDL_randf() * ((float)WINDOW_HEIGHT);
        point_speeds[i] = MIN_PIXELS_PER_SECOND + (SDL_randf() * (MAX_PIXELS_PER_SECOND - MIN_PIXELS_PER_SECOND));
    }

    Uint64 last_time = SDL_GetTicks();
    SDL_Event event;

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

        const Uint64 now = SDL_GetTicks();
        // elapsed = seconds since last iteration 
        const float elapsed = ((float)(now - last_time)) / 1000.0f;

        // Move all points every new frame
        for (int i = 0; i < SDL_arraysize(points); i++) {
            const float distance = elapsed * point_speeds[i];
            points[i].x += distance;
            points[i].y += distance;
            // Check off window size 
            if ((points[i].x >= WINDOW_WIDTH) || (points[i].y >= WINDOW_HEIGHT)) {
                // Set a new place for a point 
                if (SDL_rand(2)) { // Generate a pseudo-random number less than n for positive n
                    // Sint32 SDLCALL SDL_rand(Sint32 n)
                    points[i].x = SDL_randf() * ((float)WINDOW_WIDTH);
                    points[i].y = 0.0f;
                }
                else {
                    points[i].x = 0.0f;
                    points[i].y = SDL_randf() * ((float)WINDOW_HEIGHT);
                }
                point_speeds[i] = MIN_PIXELS_PER_SECOND + (SDL_randf() * (MAX_PIXELS_PER_SECOND - MIN_PIXELS_PER_SECOND));
            }
        }

        last_time = now;

        // draws over what was drawn before

        // Set background color
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, SDL_ALPHA_OPAQUE); // black
        SDL_RenderClear(renderer); // start with a blank canvas

        // set point color 
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, SDL_ALPHA_OPAQUE); // white
        // Draw all the points at once
        SDL_RenderPoints(renderer, points, SDL_arraysize(points)); // draw all the points

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

    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);

    SDL_Quit();

    return 0;
}

#endif

 

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