Before loading any graphics in ClanLib, you MUST have created a displaywindow first. When surfaces are created, they are converted to the most optimal format for fast blitting to the display, and therefore you need a displaywindow before loading any graphics.

Most ClanLib games will usually use resources to load its graphics, but we will start showing how the inner parts of the resource manager loads its graphics. Hopefully this should make it more clear how the whole stuff works.

To construct a surface or texture in ClanLib, we first need to load it into a surface provider. There are surface providers for many common image formats, including: CL_PCXProvider, CL_TargaProvider, CL_PNGProvider and CL_JPEGProvider.

To use these providers, simple create an instance of it, eg.

// Create a provider:
CL_TargaProvider provider("image.tga");

// Load it:
CL_Surface surface(provider);

Luckily, ClanLib provides a shortcut for the lazy among us. It can automatically figure out which provider to use based on the file-extension. Use it like this:

CL_Surface surface2("image.tga");

Although the above loading mechanism in itself is quite simple, it is often far better to seperate the description of an image from the actual game code. Instead of specifying an image by its filename and type, you use an name making more sense for the game code.

CL_ResourceManager resources("resources.xml");

CL_Surface surface("InGame/Level1/background", &resources);

The image may be in any format supported by the ClanLib surface providers, and the resource description may include transparency, subarrays and other fancy stuff. The resources.xml file includes a description of the resource that may look like this:

<resources>
	<section name="InGame">
		<section name="Level1">
			<surface name="background" file="background1.tga" />
			<surface name="walking_man" file="man.pcx" tcol="0,1,2,3" />
		</section>
	</section>
</resources>

As you can probably see, the game code no longer needs to know how the resource is physically loaded. And it is possible to change the image without recompiling the application.

The resource manager may also be attached to something else than physical files, it may be loading them from a network server, or a zipfile. The nice thing is that the game code does not need to know.

If you want more information about resources, have a look at the resource overview.