# Loading graphics, ClanLib API overview

## Abstract:

This document will discuss different ways to load graphics in ClanLib. Into surfaces, surface providers and textures. Thereafter it will discuss methods to manipulate the images without too much effords.

This document expects that you have already read the 2d API overview document. If you haven't, please do that first.

### Loading from files.

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_SurfaceProvider *provider = new CL_TargaProvider("image.tga");

    // Load it (true = delete provider when surface is deleted):
    CL_Surface *surface = CL_Surface::create(provider, true);

    // Or if you're lazy:
    CL_Surface *surface2 = CL_TargaProvider::create("image.tga");

In some cases you may want to alter the image before loading it into a surface. It might be that you think it should be cut into subsprites, or perhaps some of the colors should be transparent. To do stuff like that, ClanLib has a serie of surface providers that alters an other surface provider.

One of those providers are called CL_MaskTranscolProvider. It accepts a source image (a surface provider), and then a list of pixel values that should be made transparent.

    // First load the original image:
    CL_SurfaceProvider *provider = new CL_TargaProvider("image.tga");

    // Now modify it by making black transparent:
    unsigned int color = 0;
    CL_SurfaceProvider *new_provider =
    	new CL_MaskTranscolProvider(
    		provider, // source image
    		true,     // yes, delete source provider when we're deleted.
    		&color,   // pointer to array listening transparency colors
    		1);       // number of elements in the array.

    // Load it into a surface:
    CL_Surface *surface = CL_Surface::create(new_provider, true);

If you need to create an image from scratch, or want to compose an image from multiple other images, ClanLib provides a surface provider called CL_Canvas. At construction time, you tell how large and in what format the canvas should be in, and then afterwards you can do three things:

- Lock the canvas, party on it and then unlock it.
- Draw lines, boxes and other primitive operations.
- Draw surfaces onto the canvas.

    // Load an image:
    CL_Surface *surf = CL_TargaProvider::create("image.tga");

    // Create a canvas, size 320x200, default image format:
    CL_Canvas *canvas = new CL_Canvas(320, 200);

    // Draw a line on it:
    canvas->draw_line(0,0,100,100);

    // Draw the surface on it:
    surf->put_target(10, 10, canvas);

    // Construct a surface from it:
    CL_Surface *canvas_surf = CL_Surface::Create(canvas, true);

That should cover the basics of using surface providers.

### Loading from resources

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 = new CL_ResourceManager("resources.scr");

    CL_Surface *surface = CL_Surface::load("InGame/Level1/background", resources);

The resource 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.scr file includes a description of the resource that may look like this:

    section InGame
    {
    	section Level1
    	{
    		background = background1.tga ( // name and the file location
    			type = surface,            // resource is surface
    			tcol = (0, 1, 2, 3));      // four transparent colors.

    		walking_man = man.pcx (type = surface);
    	}
    }

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 datafile. The nice thing is that the game code doesn't know, and doesn't need to either.

If you want to load the image resource into a texture or just into surface provider, that is also possible:

    CL_Texture *texture =
    	CL_Texture::load("InGame/Level1/background", resources);

    CL_SurfaceProvider *provider =
    	CL_SurfaceProvider::load("InGame/Level1/background", resources);

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

Questions or comments, write to the ClanLib mailing list.