Question

How to change BMP image when pressing key up and key down using SDL2 in C

Answer 1

#include <stdio.h>
#include <stdbool.h>
#include <SDL.h>

static SDL_Surface* bmp = NULL;
static SDL_Surface* screen = NULL;
static SDL_Window* window = NULL;
static SDL_Surface* surface = NULL;

enum KeyPressSurfaces {
    KEY_PRESS_SURFACE_DEFAULT,
    KEY_PRESS_SURFACE_UP,
    KEY_PRESS_SURFACE_DOWN,
    KEY_PRESS_SURFACE_TOTAL
};

static SDL_Surface* keypress[KEY_PRESS_SURFACE_TOTAL];

bool init() {
    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        printf("SDL_Init Error: %s\n", SDL_GetError());
        return false;
    }
    else {
        window = SDL_CreateWindow("SDL", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
                                    800, 600, SDL_WINDOW_SHOWN);
        if (window == NULL) {
            printf("SDL_CreateWindow Error: %s\n", SDL_GetError());
            return false;
        }
        else {
            screen = SDL_GetWindowSurface(window);
        }
    }

    return true;
}

SDL_Surface* loadBMP(char path[]) {
    SDL_Surface* bmp = SDL_LoadBMP(path);
    if (bmp == NULL) {
        printf("loadBMP Error: %s\n", SDL_GetError());
    }

    return bmp;
}

bool loadSurface() {
    keypress[KEY_PRESS_SURFACE_DEFAULT] = loadBMP("assets/RAY.BMP");
    if (keypress[KEY_PRESS_SURFACE_DEFAULT] == NULL) {
        printf("loadSurface Error: %s\n", SDL_GetError());
        return false;
    }

    keypress[KEY_PRESS_SURFACE_UP] = loadBMP("assets/LAND.BMP");
    if (keypress[KEY_PRESS_SURFACE_UP] == NULL) {
        printf("loadSurface Error: %s\n", SDL_GetError());
        return false;
    }

    keypress[KEY_PRESS_SURFACE_DOWN] = loadBMP("assets/MARBLES.BMP");
    if (keypress[KEY_PRESS_SURFACE_DOWN] == NULL) {
        printf("loadSurface Error: %s\n", SDL_GetError());
        return false;
    }

    return true;
}


void close() {
    for (int i = 0; i < KEY_PRESS_SURFACE_TOTAL; i++) {
        SDL_FreeSurface(keypress[i]);
        keypress[i] = NULL;
    }

    SDL_DestroyWindow(window);
    window = NULL;

    SDL_Quit();
}

int main(int argc, char* argv[]) {
    if (!init()) {
        printf("init error\n");
    }
    else {
        if (!loadSurface()) {
            printf("Failed to load BMP!\n");
        }
        else {
            surface = keypress[KEY_PRESS_SURFACE_DEFAULT];

            SDL_Event event;
            bool quit = false;
            while (quit == false) {
                while (SDL_PollEvent(&event)) {
                    if (event.type == SDL_QUIT) {
                        quit = true;
                    }
                    else if (event.type = SDL_KEYDOWN) {
                        switch (event.key.keysym.sym) {
                        case SDLK_UP:
                            surface = keypress[KEY_PRESS_SURFACE_UP];
                            break;
                        case SDLK_DOWN:
                            surface = keypress[KEY_PRESS_SURFACE_DOWN];
                            break;
                        default:
                            surface = keypress[KEY_PRESS_SURFACE_DEFAULT];
                            break;
                        }
                    }
                }
                SDL_BlitSurface(surface, NULL, screen, NULL);

                SDL_UpdateWindowSurface(window);
            }
        }
    }
    close();

    return 0;
}

 

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