SDL Game Development
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Installing SDL_image

So far we have only been loading BMP image files. This is all that SDL supports without any extensions. We can use SDL_image to enable us to load many different image file types such as BMP, GIF, JPEG, LBM, PCX, PNG, PNM, TGA, TIFF, WEBP, XCF, XPM, and XV. First we will need to clone the latest build of SDL_image to ensure it will work with SDL 2.0:

  1. Open up the TortoiseHg workbench and use Ctrl + Shift + N to clone a new repository.
  2. The repository for SDL_image is listed on http://www.libsdl.org/projects/SDL_image/ and http://hg.libsdl.org/SDL_image/. So let's go ahead and type that into the Source box.
  3. Our destination will be a new directory, C:\SDL2_image. After typing this into the Destination box, hit clone and wait for it to complete.
  4. Once you have created this folder, navigate to our C:\SDL2_image cloned repository. Open up the VisualC folder and then open the SDL_image_VS2010 VC++ project with Visual Studio 2010 express.
  5. Right-click on the SDL2_image project and then click on Properties. Here we have to include the SDL.h header file. Change the configuration to All Configurations, navigate to VC++ Directories, click on the Include Directories drop-down, and then on <Edit…>. Here we can put in our C:\SDL2\include\ directory.
  6. Next move to Library Directories and add our C:\SDL2\lib\ folder. Now navigate to Linker | Input | Additional Dependencies and add SDL2.lib.
  7. Click on OK and we are almost ready to build. We are now using SDL2.lib, so we can remove the SDL.lib and the SDLmain.lib files from the SDL_image project. Locate the files in the solution explorer, right-click and then remove the files. Change the build configuration to release and then build.
  8. An error about being unable to start the program may appear. Just click on OK and we can close the project and continue.
  9. There will now be a Release folder inside our C:\SDL2_image\VisualC\ folder. Open it and copy the SDL_image.dll to our game's executable folder.
  10. Next copy the SDL2_image.lib file into our original C:\SDL2\lib\ directory. Also copy the SDL_image header from C:\SDL2_image\ to the C:\SDL2\include\ directory.
  11. We just have a few more libraries to get and we are done. Download the SDL_image-1.2.12-win32.zip file (or the x64 if you are targeting a 64 bit platform) from http://www.libsdl.org/projects/SDL_image/. Extract all and then copy all of the .dll files apart from SDL_image.dll into our game's executable folder.
  12. Open up our game project and go into its properties. Navigate to Linker | Input | Additional Dependencies and add SDL2_image.lib.
  13. We have now installed SDL_image and can start to load all kinds of different image files. Copy the animate.png and animate-alpha.png images from the source downloads to our games assets folder and we can start loading PNG files.

Using SDL_image

So we have the library installed, now how do we use it? It is simple to use SDL_image in place of the regular SDL image loading. In our case we only need to replace one function and also add #include <SDL_image.h>.

SDL_Surface* pTempSurface = SDL_LoadBMP("assets/animate.bmp");

The preceding code will be changed as follows:

SDL_Surface* pTempSurface = IMG_Load("assets/animate.png");

We are now loading a .png image. PNG files are great to work with, they have a small file size and support an alpha channel. Let's perform a test. Change our renderer clear color to red.

SDL_SetRenderDrawColor(m_pRenderer, 255,0,0,255);

You will see that we still have our black background from the image we are using; this is definitely not ideal for our purposes.

When using PNG files, we can resolve this by using an alpha channel. We remove the background from the image and then when we load it, SDL will not draw anything from the alpha channel.

Let's load this image and see how it looks:

SDL_Surface* pTempSurface = IMG_Load("assets/animate-alpha.png");

This is exactly what we want:

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