Common message hooks

Each WEL library component implements a set of routines for processing the most common messages that a component receives. For example, looking at WEL_FRAME_WINDOW , you will see that there are many features which begin on_. Each of these features enable the user to know when a specific event has occurred, and to perform the appropriate processing as a result of this event. Most of the time, you will only be interested in a small subset of these, necessary to your program. For example, below is the code for on_paint: on_paint (paint_dc: WEL_PAINT_DC; invalid_rect: WEL_RECT) --Draw a centered text do end

An on_paint message corresponds to the Wm_paint message generated by Windows whenever it needs to re-paint a window, and if you look at the feature, you can see that the arguments are a WEL_PAINT_DC and a WEL_RECT . which are relevant to this message. By redefining this feature (and others as required), your code will be able to respond appropriately to windows events.

Note: See step2 in the tutorial for a simple demonstration involving the re-definition of on_left_button_down.

For different messages received by a control, the arguments will differ (sometimes there are none), but those arguments will always be relevant to the message. For example, on_menu_command from WEL_COMPOSITE_WINDOW has an INTEGER as an argument, the value of which is a unique menu identifier.

Note: Not all windows events have a corresponding "on_" message hook defined in WEL. If you wish to process a Windows message that does not correspond to one of the available features, you will need to redefine process_message.