Stan wrote:
> Thanks Greg & Matt for your thorough explanation. However,
> go back to the compilable example and replace the line
> new Outer(475, 40, 20, 20, "Your Message Here");
> with
> new Inner(475, 40, 20, 20, "Your Message Here");
With the above modification, the widget is just drawing
the label outside its own perimeter, not outside its parent.
The key word here being "parent":
Greg wrote:
> This is normal; FLTK does not guarantee predictable behavior
> if a child draws outside the bounds of its parent(s). This breaks
> the rule of how window damage is calculated.
In simple cases, a widget may draw outside its own perimeter
and depend on damage to its immediate parent to tell it to redraw.
(hope you're reading in fixed width font; here comes some ascii-art)
For instance, when FL_ALIGN_INSIDE is not specified, the label
for the widget will draw outside the widget's perimeter, such
as this simple case of an Fl_Input inside a window:
______________________________________________________
| Window |
|------------------------------------------------------|
| |
| ----------------------- |
| My Input Field: | | |
| ----------------------- |
|______________________________________________________|
The key here is the Fl_Input is positioned to account for the
floating label; the widget has been positioned so that the label
fits /inside/ its parent, and doesn't float off the edge of the
window.
This seems obvious, but it's the point that's missed in the
original example.
The same rule goes for more complex hierarchies; if the
Fl_Input is then placed inside a parenting group, it must
be positioned such that it and its label are /inside/ the group, eg:
______________________________________________________
| Window |
|------------------------------------------------------|
| Group |
| ------------------------------------------------ |
| | ----------------------- | |
| | My Input Field: | | | |
| | ----------------------- | |
| ------------------------------------------------ |
|______________________________________________________|
What would be bad is if the Fl_Input is placed inside the group
such that the floating label is /not/ accounted for, which is
what is what is wrong with the original example:
______________________________________________________
| Window |
|------------------------------------------------------|
| Group |
| ------------------------------ |
| | ----------------------- | |
| My Input Field: | | | |
| | ----------------------- | |
| ------------------------------ |
|__________________^___________________________________|
|
Group is clipping off the label
This is bad, and what the original example showed.
For predictable redraw behavior, children must have all their
graphics drawn within the perimeter of their parent. It's an
easy rule to remember, and makes sense. Just be sure to apply
it, even in complex hierarchies.
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