如何在 sdl2 上按下键盘时更改图像

Question

我一直在使用 SDL2.0 和 C 开发这款游戏，但遇到了麻烦。正如标题所说，我想在用户按下键盘时更改图像，但它不会work.So我想知道代码哪里错了。

这是代码。

#include <stdio.h>
#include <sdl2/SDL.h>
#include <sdl2/SDL_image.h>


int main(int argc, char* args[]){
    bool quit = false;
    SDL_Event event;
 
    SDL_Init(SDL_INIT_VIDEO);
 
    SDL_Window * window = SDL_CreateWindow("SDL2 Displaying Image",
    SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640, 480, 0);
    SDL_Renderer * renderer = SDL_CreateRenderer(window, -1, 0);
    SDL_Surface * image = SDL_LoadBMP("opening_ps1.bmp");     
    SDL_Texture * texture = SDL_CreateTextureFromSurface(renderer, image);
 
    while (!quit){
        SDL_WaitEvent(&event);
        SDL_RenderCopy(renderer, texture, NULL, NULL);
        SDL_RenderPresent(renderer);
        
        while(SDL_PollEvent(&event)){
            if(event.type == SDL_QUIT){
                quit = true;
                break;
            }
            
            if(event.type == SDL_KEYDOWN){
                switch(event.key.keysym.sym){
                    case SDL_SCANCODE_A:
                        quit = false;
                        SDL_Renderer * renderer1 = SDL_CreateRenderer(window, -1, 0);
                        SDL_Surface * image1 = SDL_LoadBMP("opening_2.bmp");     
                        SDL_Texture * texture1 = SDL_CreateTextureFromSurface(renderer1, image1);
                        SDL_RenderClear(renderer);
                        SDL_RenderCopy(renderer1, texture1, NULL, NULL);
                        SDL_RenderPresent(renderer1);
                        break;
                }
            }
        }
    }

    SDL_FreeSurface(image);    
    SDL_DestroyWindow(window);

    SDL_Quit();
 
    return 0;
    }

Answer 1

这是你的代码完美运行，让我解释一下它是如何工作的！请不要忘记更改文件名，我用的是 png，但你可以用 bmps 做同样的事情。

SDL_image.h

首先，我假设您可能想要加载其他类型的文件，而不仅仅是 bmps，并且由于您在导入中有该库，我认为我可以将其包含在代码中！

主循环

你有一个双循环，这是你在这里并不真正需要的东西，我们可以有一个无限循环和里面的中断条件。

SDL_FreeSurface

由于创建纹理后我们不再需要表面，我们可以立即释放它们

SDL_SCANCODE_A

这是您将 event.key.keysym.sym 的结果与之进行比较的结果，但是 event.key.keysym.sym 的类型是 SDL_Keycode 所以您必须将其与SDLK_a进行比较，以便在按下键a时触发图像的变化

    #include <SDL2/SDL.h>
    #include <SDL2/SDL_image.h>
    #include <stdbool.h>
    
    int main(int argc, char *args[])
    {
        SDL_Event event;
    
        SDL_Init(SDL_INIT_VIDEO);
        IMG_Init(IMG_INIT_PNG);
    
        SDL_Window *window = SDL_CreateWindow("SDL2 Displaying Image",
                                              SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640, 480, 0);
        SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, 0);
        SDL_Surface *image = IMG_Load("akward.png");
        SDL_Texture *texture = SDL_CreateTextureFromSurface(renderer, image);
        SDL_FreeSurface(image);
        SDL_RenderCopy(renderer, texture, NULL, NULL);
        SDL_RenderPresent(renderer);
    
        while (1)
        {
            SDL_PollEvent(&event);
            if (event.type == SDL_QUIT)
            {
                break;
            }
    
            if (event.type == SDL_KEYDOWN)
            {
                switch (event.key.keysym.sym)
                {
                case SDLK_a:
                    SDL_Surface *image1 = IMG_Load("output.png");
                    SDL_Texture *texture1 = SDL_CreateTextureFromSurface(renderer, image1);
                    SDL_FreeSurface(image1);
                    SDL_RenderClear(renderer);
                    SDL_RenderCopy(renderer, texture1, NULL, NULL);
                    SDL_RenderPresent(renderer);
                    break;
                }
            }
        }
        
        SDL_DestroyWindow(window);
    
        SDL_Quit();
    
        return 0;
    }

编辑：

这是允许您从目录中获取所有图像并显示它们的代码！如果您有兴趣，我会做一个简短的解释。首先，我写了一个宏，允许您指定目录中的图像数量，请确保它是正确的数量！我已经放了 5 个用于测试目的！ #define IMG_NUMBER 5

我又创建了两个函数，my_str_concat只是为了连接目录名和文件名，所以可以用IMG_Load打开. create_texture_array 创建一个纹理数组，以便之后的主函数可以使用它们

    #include <SDL2/SDL.h>
    #include <SDL2/SDL_image.h>
    #include <stdbool.h>
    #include <dirent.h>
    #include <errno.h>
    
    #define IMG_NUMBER 5
    
    char * my_str_concat(const char * input_directory, char * file_name)
    {
        size_t input_directory_size = strlen(input_directory);
        //The + 257 is for the max size of file_name
        char * res = malloc(sizeof(char)*(input_directory_size+257));
        strcpy(res,input_directory);
        strcat(res,file_name);
        return res;
    }
    
    SDL_Texture ** create_texture_array(const char * input_directory,SDL_Renderer *renderer)
    {
        SDL_Texture ** texture_array = malloc(sizeof(SDL_Texture *) * IMG_NUMBER);
        int i = 0;
        DIR *images_dir;
    
        if (NULL == (images_dir = opendir(input_directory)))
        {
            fprintf(stderr, "Error : Failed to open input directory - %s\n", strerror(errno));
            return NULL;
        }
        struct dirent * image_file;
        while((image_file = readdir(images_dir)))
        {
            //We don't want to read current and parent directories!
            if (!strcmp (image_file->d_name, "."))
            {
                continue;
            }
            if (!strcmp (image_file->d_name, ".."))
            {
                continue;
            }
    
            char * relative_file_path = my_str_concat(input_directory,image_file->d_name);
            printf("%s\n",relative_file_path);
            SDL_Surface *image = IMG_Load(relative_file_path);
            free(relative_file_path);
            SDL_Texture *texture = SDL_CreateTextureFromSurface(renderer, image);
            SDL_FreeSurface(image);
            texture_array[i] = texture;
            i++;
        }
        return texture_array;
    }
    
    void free_array(SDL_Texture ** arr, size_t size)
    {
        for (size_t i = 0; i < size; i++)
        {
            SDL_DestroyTexture(arr[i]);
        }
    }
    
    int main(int argc, char *args[])
    {
        SDL_Event event;
    
        int i = 0;
    
        SDL_Init(SDL_INIT_VIDEO);
        IMG_Init(IMG_INIT_PNG);
    
    
        SDL_Window *window = SDL_CreateWindow("SDL2 Displaying Image",SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640, 480, 0);
    
        SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, 0);
    
        SDL_Texture ** texture_array = create_texture_array("img/",renderer);
    
        SDL_RenderCopy(renderer, texture_array[0], NULL, NULL);
        SDL_RenderPresent(renderer);
    
    
        while (1)
        {
            SDL_PollEvent(&event);
            if (event.type == SDL_QUIT)
            {
                break;
            }
    
            if (event.type == SDL_KEYDOWN && i+1 < IMG_NUMBER)
            {
                switch (event.key.keysym.sym)
                {
                case SDLK_a:
                    i++;
                    SDL_RenderClear(renderer);
                    SDL_RenderCopy(renderer, texture_array[i], NULL, NULL);
                    SDL_RenderPresent(renderer);
                    break;
                }
            }
        }
    
        free_array(texture_array,IMG_NUMBER);
        SDL_DestroyWindow(window);
    
        SDL_Quit();
    
        return 0;
    }

希望对您有所帮助！如果这确实回答了您的问题，请不要犹豫将此答案标记为正确！最好的问候，

如何在 sdl2 上按下键盘时更改图像

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