My step by step guides for SDL3 to build for Android and WebAssembly

SDL Development
19

Mouse click event handler using SDL3

Demo in the browser (click on the canvas)

int SDL_AppEvent(void *appstate, const SDL_Event *event)
{
    auto *app = (AppContext *)appstate;

    switch (event->type)
    {
        case SDL_EVENT_MOUSE_BUTTON_DOWN:
        {
            if (event->button.button == SDL_BUTTON_LEFT)
            {
                int x = event->button.x;
                int y = event->button.y;
                std::cout << "x: " << x << ", y = " << y << std::endl;
            }
            break;
        }
        case SDL_EVENT_QUIT:
        {
            app->app_quit = SDL_TRUE;
            break;
        }
        default:
        {
            break;
        }
    }

    return 0;
}

main.cpp

#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h>
#include <cmath>
#include <iostream>

#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#include <emscripten/html5.h>
#endif // __EMSCRIPTEN__

struct AppContext
{
    SDL_Window *window;
    SDL_Renderer *renderer;
    SDL_bool app_quit = SDL_FALSE;
};

int SDL_Fail()
{
    SDL_LogError(SDL_LOG_CATEGORY_CUSTOM, "Error %s", SDL_GetError());
    return -1;
}

int SDL_AppInit(void **appstate, int argc, char *argv[])
{
    // init the library, here we make a window so we only need the Video capabilities.
    if (SDL_Init(SDL_INIT_VIDEO))
    {
        return SDL_Fail();
    }

    // create a window
    SDL_Window *window = SDL_CreateWindow("Window", 352, 430, SDL_WINDOW_RESIZABLE);
    if (!window)
    {
        return SDL_Fail();
    }

    SDL_Renderer *renderer = SDL_CreateRenderer(window, NULL);
    if (!renderer)
    {
        return SDL_Fail();
    }

    // print some information about the window
    SDL_ShowWindow(window);
    {
        int width, height, bbwidth, bbheight;
        SDL_GetWindowSize(window, &width, &height);
        SDL_GetWindowSizeInPixels(window, &bbwidth, &bbheight);
        SDL_Log("Window size: %ix%i", width, height);
        SDL_Log("Backbuffer size: %ix%i", bbwidth, bbheight);
        if (width != bbwidth)
        {
            SDL_Log("This is a highdpi environment.");
        }
    }

    // set up the application data
    *appstate = new AppContext {
        window,
        renderer,
    };

    SDL_Log("Application started successfully!");

    return 0;
}

int SDL_AppEvent(void *appstate, const SDL_Event *event)
{
    auto *app = (AppContext *)appstate;

    switch (event->type)
    {
        case SDL_EVENT_MOUSE_BUTTON_DOWN:
        {
            if (event->button.button == SDL_BUTTON_LEFT)
            {
                int x = event->button.x;
                int y = event->button.y;
                std::cout << "x: " << x << ", y = " << y << std::endl;
            }
            break;
        }
        case SDL_EVENT_QUIT:
        {
            app->app_quit = SDL_TRUE;
            break;
        }
        default:
        {
            break;
        }
    }

    return 0;
}

int SDL_AppIterate(void *appstate)
{
    auto *app = (AppContext *)appstate;

    // draw a color
    auto time = SDL_GetTicks() / 1000.f;
    auto red = (std::sin(time) + 1) / 2.0 * 255;
    auto green = (std::sin(time / 2) + 1) / 2.0 * 255;
    auto blue = (std::sin(time) * 2 + 1) / 2.0 * 255;

    SDL_SetRenderDrawColor(app->renderer, red, green, blue, SDL_ALPHA_OPAQUE);
    SDL_RenderClear(app->renderer);
    SDL_RenderPresent(app->renderer);

    return app->app_quit;
}

void SDL_AppQuit(void *appstate)
{
    auto *app = (AppContext *)appstate;
    if (app)
    {
        SDL_DestroyRenderer(app->renderer);
        SDL_DestroyWindow(app->window);
        delete app;
    }

    SDL_Quit();
    SDL_Log("Application quit successfully!");
}