A simple approach to managing a large number of interactive menu choice.
Tcl is really good at making the difficult easy. Imagine a paint program with a range of tools, the action of which will differ yet they will all act to change a single buffer. What then, is the simplest way of for the application to decide how to pass information about user interaction over to the appropriate functionality. I remember seeing, many years ago, the source code for the AT&T Tips paint software (running on now ancient Targa and Vista display buffers). Here the operator would make a choice, a global variable was set and the input data passed on after entering a cascade of switch/case operations. Would it not be simpler to have a unified series of arguments passed to a handling function the pointer to which is set rather than a variable? This is how Gtk handles event programming and we can use a similar principle in our Gnocl scripts.
Consider the following code segment to make a typical paint toolbar:
All looks pretty straight forward, but further examination of the -onClicked command shows that the global variable handler(active) has been set to the name of of this widget. This, of course assumes that a following procedure exists. The following example is for a simple pixel drawing pencil.
w -the widget-id of the calling widget
x -the cursor x coordinate
y -the curose y coordinate
b -the button event
m -the state of the keyboard modifiers
Now, whenever user interaction occurs in the image drawing/edit areas, all event information can be passed directly as the following snippet shows. All that has happened is that the name the handler script has changed -simple!
Here a gnocl::image, which has no inherent signal mask is contained in a gnocl::eventBox. Whenever a motion event occurs, the interpreter will involk the preselected handling function.
The basic notion then is quite simple and potentially saves a whole pile checking issues. There's only one issue though. The -name option used by Glade produced UIs, so care must be taken to ensure consistency between proc and widget naming during the layout process.
Gnocl Cookbook >