使用带有 LibZip 的 SDL_image 和 SDL_RWops 将 png 从 zip 加载到表面上，但无法识别 png

Question

相关代码：

  zip_stat_t filestat;
  uint64_t filetotal = 0;
  SDL_RWops* rwop = SDL_AllocRW();

//bunch of code that's not relevant to the matter goes here

  std::vector<char> rwbuffer(filestat.size);
  rwop = SDL_RWFromMem(rwbuffer.data(), filestat.size);
  while(filetotal < filestat.size)
  {
    char buffer[256];
    int64_t length;
    //read the file into the buffer
    length = zip_fread(file, buffer, 256);
    if (length == -1)
    {
      u_error(std::cerr, CC_ERROR_ZIP, "zip_fread");
      zip_fclose(file);
      SDL_FreeRW(rwop);
      return false;
    }
    //write the buffer into the rwop stream
    if ( (uint16_t)length != SDL_RWwrite(rwop, buffer, 1, (size_t)length) )
    {
      u_error(std::cerr, CC_ERROR_SDL, "SDL_RWwrite");
      zip_fclose(file);
      SDL_FreeRW(rwop);
      return false;
    }
    //Increment the count so that the loop ends
    filetotal += length;
  }
  zip_fclose(file);
  //Put it onto a surface
  SDL_Surface* surf_load = IMG_Load_RW(rwop, 0);
  if(surf_load == NULL)
  {
    u_error(std::cerr, CC_ERROR_IMAGE, "IMG_Load_RW");
    SDL_FreeRW(rwop);
    u_cleanup(surf_load);
    return false;
  }

//...

我已经用调试器转储了矢量 rwbuffer 的内容，它是一个有效的 png，但 IMG_Load_RW 仍然给我一个错误“不支持的图像格式”。我已经安装了 libpng 并且 IMG_Init 似乎工作正常，所以 SDL_image 库必须工作。显然 libzip 给了我正确的数据。我很困惑为什么会出错。

Answer 1

我想通了。在我读取数据的while循环结束时，RWops流的查找值在文件末尾，并且IMG_LoadPNG_RW不会重置它，所以我必须手动 SDL_RWseek(rwop, 0, RW_SEEK_SET);在while循环完成后读取png数据。

  //Return the seek pointer of the RWop to the beginning so that the file can be read
  SDL_RWseek(rwop,0,RW_SEEK_SET);
  //Put it onto a surface
  SDL_Surface* surf_load = IMG_Load_RW(rwop, 0);
  if(surf_load == NULL)
  {
    u_error(std::cerr, CC_ERROR_IMAGE, "IMG_Load_RW");
    SDL_FreeRW(rwop);
    u_cleanup(surf_load);
    return false;
  }

Answer 2

如果您在调用IMG_Load_RW(rwop, 0); 之前调用SDL_FreeRW(rwop);，那么您将一无所获。

如果没有问题，那么使用：

IMG_LoadPNG_RW instread IMG_Load_RW 也可以IMG_isPNG 进行检查。

在其他方面，您似乎在 SDL i SDL_Image 之间存在版本相关性错误。如果你使用 SDL2，那么也使用 SDL2_image lib。

更新

  zip_stat_t filestat;
  uint64_t filetotal = 0;
  SDL_RWops* rwop = SDL_AllocRW();

//bunch of code that's not relevant to the matter goes here

  std::vector<char> rwbuffer(filestat.size);
  rwop = SDL_RWFromMem(rwbuffer.data(), filestat.size);
  while(filetotal < filestat.size)
  {
    char buffer[256];
    int64_t length;
    //read the file into the buffer
    length = zip_fread(file, buffer, 256);
    if (length == -1)
    {
      u_error(std::cerr, CC_ERROR_ZIP, "zip_fread");
      zip_fclose(file);
      SDL_FreeRW(rwop);
      return false;
    }
    //write the buffer into the rwop stream
    if ( (uint16_t)length != SDL_RWwrite(rwop, buffer, 1, (size_t)length) )
    {
      u_error(std::cerr, CC_ERROR_SDL, "SDL_RWwrite");
      zip_fclose(file);
      SDL_FreeRW(rwop);
      return false;
    }
    //Increment the count so that the loop ends
    filetotal += length;
  }
  zip_fclose(file);
  //Put it onto a surface
  SDL_Surface* surf_load = IMG_LoadPNG_RW(rwop, 0);
  if(surf_load == NULL)
  {
    u_error(std::cerr, CC_ERROR_IMAGE, "IMG_Load_RW");
    SDL_FreeRW(rwop);
    u_cleanup(surf_load);
    return false;
  }