Progress
Programming
Handbook
Z order and Field Groups
If you overlap widgets in an application, Progress must determine which widget to place on top. Within a frame, there are three layers:
- The foreground layer, with all the nondrawable field-level widgets in the foreground field group. This is the topmost layer. (A drawable field-level widget is a rectangle or image.)
- The background layer, with all the nondrawable field-level widgets in the background field group. This is the next topmost layer.
- The drawable layer, with all the drawable field-level widgets from all of the field groups. This is the bottommost layer.
Within each z layer, widgets also have a z order (that is, one foreground button may be on top of another foreground button). However, Progress places all nondrawable foreground widgets on top of all nondrawable background widgets, and places all drawable widgets on the bottom layer. For example, if you have a text widget in the background and an image in the foreground, the text widget appears on top of the image.
NOTE: Figure 19–10 shows the relative z-order positions of the foreground and background field groups (Z–Axis), but does not show the separate drawable layer derived from both of these field groups. The drawable layer is not a field group, itself, but a z-order layer under the background field group (extreme left of Figure 19–10) containing drawable widgets from both field group layers.If you want an application to be portable to character displays, you should avoid using overlapping widgets. In a character display, if two field-level widgets overlap, one of the widgets may appear, both may appear, or some part of each may appear.
Copyright © 2004 Progress Software Corporation www.progress.com Voice: (781) 280-4000 Fax: (781) 280-4095 |