SDL Renderer + A Moving Image

sdl_image_move_example.cpp

#include <SDL.h>
#include <iostream>
#include <sstream>
#include <string>

int main(int argc, char *argv[])
{
    int screen_width = 1024, screen_height = 768;
    SDL_Window* main_window = NULL;
    SDL_Renderer* renderer = NULL;
    SDL_Event event = { 0 };
    bool should_quit = false;
    const std::string image_file = "..\\img\\image.bmp";
    SDL_Surface* image_surface = NULL;
    SDL_Texture* image_texture = NULL;
    SDL_Rect image_destination = { 0 };
    int image_width = 0;
    int image_height = 0;
    std::stringstream error;

    try {

        if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS) < 0) {
            error << "Failed to initialize SDL: " << SDL_GetError();
            throw(error.str());
        }

        if ((main_window = SDL_CreateWindow("Use the arrow keys!", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, screen_width, screen_height, 0)) == 0) {
            error << "Failed to create a window: " << SDL_GetError();
            throw(error.str());
        }

        if ((renderer = SDL_CreateRenderer(main_window, -1, 0)) == 0) {
            error << "Failed to create the renderer: " << SDL_GetError();
            throw(error.str());
        }

        // LOAD THE BACKGROUND BITMAP INTO A SURFACE & CONVERT IT TO A TEXTURE:
        // ... the surface is only temporary, but rendering requires a texture.
        if ((image_surface = SDL_LoadBMP(image_file.c_str())) == NULL) {
            // Failure ...
            error << "Failed load image \"" << image_file << "\": " << SDL_GetError();
            throw(error.str());
        }
        else {
            // Image will initially appear centered on the screen:
            image_width = image_surface->w;
            image_height = image_surface->h;
            image_destination.x = (screen_width / 2) - (image_width / 2);
            image_destination.y = (screen_height / 2) - (image_height / 2);
            image_destination.w = image_width;
            image_destination.h = image_height;

            // Success (Continue converting it to a texture so it's usable) ...
            image_texture = SDL_CreateTextureFromSurface(renderer, image_surface);
            SDL_FreeSurface(image_surface); // The back surface is no longer needed now that we have a texture for it.
            image_surface = NULL;
            // If texture creation failed, now is the time to do something about it:
            if (image_texture == NULL) {
                // Failure ...
                error << "Failed to create texture from surface: " << SDL_GetError();
                throw(error.str());
            }
        }

        // PRIMARY & EVENT LOOP:
        while (!should_quit) {
            while (SDL_PollEvent(&event)) {
                switch (event.type) {
                case SDL_QUIT:
                    should_quit = 1;
                    break;
                case SDL_KEYDOWN:
                    switch (event.key.keysym.sym) {
                    case SDLK_ESCAPE:
                        should_quit = 1;
                        break;
                    }
                    break;
                }
            }

            // CHECK THE KEYBOARD STATE FOR MOVEMENT KEYS:
            // If you had used events for this instead (SDL_KEYDOWN/UP) you 
            // would have only been able to act on one key press at a time.

            const Uint8 *state = SDL_GetKeyboardState(NULL);
            if (state[SDL_SCANCODE_LEFT]) {
                if (image_destination.x > 0) image_destination.x -= 1;
            }
            if (state[SDL_SCANCODE_RIGHT]) {
                if (image_destination.x + image_width < screen_width) image_destination.x += 1;
            }
            if (state[SDL_SCANCODE_UP]) {
                if (image_destination.y > 0) image_destination.y -= 1;
            }
            if (state[SDL_SCANCODE_DOWN]) {
                if (image_destination.y + image_height < screen_height) image_destination.y += 1;
            }

            // RENDERING:

            // Clear the background:
            SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
            SDL_RenderClear(renderer);

            // Render the entire logo to the center of the screen:
            SDL_RenderCopy(renderer, image_texture, NULL, &image_destination);

            SDL_RenderPresent(renderer);
        }

    }
    catch (std::string error_str) {
        std::cout << error_str << std::endl;
    }

    if (image_texture) SDL_DestroyTexture(image_texture);
    if (renderer) SDL_DestroyRenderer(renderer);
    if (main_window) SDL_DestroyWindow(main_window);
    SDL_Quit();

    return 0;
}