Loading and Saving Images with SDL2

We have seen in past articles how we can load basic image formats (such as BMP, PNG and JPG) using SDL2 and SDL_image 2.0. In this article, we’re going to learn a bit more about the image formats we can load and save with these libraries.

Saving BMPs

Just like SDL2 gives us SDL_LoadBMP() to load BMP images, it also gives us SDL_SaveBMP() to save them. There is no need for SDL_image to use either of these functions, because they are in core SDL2.

Since we know from past articles that we can use SDL_image to load a few other formats, it is then easy to write a small program to convert from PNG (or any other of the supported format) to a BMP:

#include <SDL.h>
#include <SDL_image.h>

int main(int argc, char ** argv)
{
    SDL_Surface * image = IMG_Load("image.png");
    SDL_SaveBMP(image, "out.bmp");
    SDL_FreeSurface(image);

    return 0;
}

As you can see, it is not even necessary to initialize SDL2. We simply load the PNG file, and save it back to disk as BMP.

Saving PNGs

As someone pointed out in this forum thread, there are two undocumented functions that allow you to save a PNG:

sdl2-savepng

Thus, we can use this function to do the opposite conversion from BMP to PNG:

    SDL_Surface * image = SDL_LoadBMP("image.bmp");
    IMG_SavePNG(image, "out.png");
    SDL_FreeSurface(image);

Loading other formats

Disgracefully, there is no documentation for SDL_image 2.0 at the time of writing this article. The ‘documentation’ links on the SDL_image 2.0 homepage are actually for SDL_image 1.2.8, which is very misleading.

The old documentation for IMG_Init() shows three supported flag values you can pass in: IMG_INIT_JPG, IMG_INIT_PNG and IMG_INIT_TIF. Through intellisense I’ve discovered a fourth one for the WEBP format:

sdl2-init-webp

I’ve also found that calling IMG_Init() and IMG_Quit() is completely unnecessary, as everything seems to work without them.

Finally, despite the few init flags mentioned above, there are many more formats support by IMG_Load(). I’ve tested WEBP, PCX, GIF, PPM, TIF, TGA and BMP with success; and there are other formats in the old documentation that may be supported.

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