Perl Graphics Programming

Object-Oriented Versus Procedural Scripting

If you are familiar with the structure of Gimp plug-ins written in C, you will immediately notice a few details of the previous example that differ between Perl and C. Because Gimp-Perl is a scripting extension that acts as a high-level interface to libgimp (the Gimp API), you do not necessarily have to use the clumsy PDB-style calling syntax that you must use in C.

All libgimp functions and additional plug-ins are registered in the Procedural Database. The entries in the PDB serve to document the Gimp API; you can use the PDB Browser (found under the Xtns menu) to search the API. As shown in Figure 5-2, the browser displays the function interfaces using C syntax. For example, if you want to copy a layer using the function gimp_layer_copy( ), you would look up the function in the browser and write the function call (in C) as:

ret_vals = gimp_run_procedure("gimp_layer_copy",
                              &nret_vals,
                              PARAM_LAYER, layerID,
                              PARAM_INT32, TRUE,
                              PARAM_END);

Figure 5-2. The Procedural Database browser

In Perl you can call the function more simply:

$new_layer = gimp_layer_copy($layer, 1);

Note that the style shown above can be used only if you have imported the Gimp API function names with the :auto tag. Otherwise, you would have to specify the package name:

$new_layer = Gimp::gimp_layer_copy($layer, 1);

You can get away with sticking to the simple procedural-style calling ...