SDL (Simple DirectMedia Layer) - Rendering other image formats

Rendering other image formats requires the use of another SDL library: SDL_image. However, the process of rendering different image formats is very much the same as rendering BMP images. In this section, we'll demonstrate how to render a PNG file onto a window.

^{You can download the source code of this section in this GitLab repository. All source code is stored in this group.}

Importing the SDL_image library

We'll import the SDL_image library, in wikibook.h, in the following fashion:

#ifdef _WIN32
#include <SDL/SDL.h> /* Windows-specific SDL2 library */
#include <SDL_image.h>
#else
#include <SDL2/SDL.h> /* macOS- and GNU/Linux-specific */
#include <SDL2/SDL_image.h>
#endif

Initialising the image subsystem

Right after initialising the SDL subsytems, we would need to initialise the image subsystem using IMG_Init. Given the parameter int flags, it returns flags on success.

We'll want to render a PNG file so we would want to use the flag IMG_INIT_PNG. There are other flags like IMG_INIT_JPG (check IMG_Init for more information). To initialise multiple flags use the | OR operator, for example:

const int FLAGS = IMG_INIT_PNG | IMG_INIT_JPG;

You'll also have to use IMG_Quit to close the subsystem.

/* Initialise SDL_image */
const int FLAGS = IMG_INIT_PNG;

if (IMG_Init(FLAGS) != FLAGS) {
  fprintf(stderr, "SDL_image failed to initialise: %s\n", IMG_GetError());
  return -1;
}

/* Automatically execute IMG_Quit at exit */
atexit(IMG_Quit);

Since we're using SDL_image, we have to use IMG_GetError in place of SDL_GetError.

Loading the image

Loading the image is very simple, just use the IMG_Load function on a SDL_Surface. Like with IMG_Init, we must use IMG_GetError.

wb->image = IMG_Load(WB_IMAGE_PATH);

if (wb->image == NULL) {
  fprintf(stderr, "WikiBook failed to load image: %s\n", IMG_GetError());
  return -1;
}

Remember, to make sure that the file path to the image is correct, i.e. WB_IMAGE_PATH! We're rendering a PNG image!