Float, line 1/3
Float, line 2/3
Float, line 3/3
Stacking Context 1
Stacking Context 2
The rendering will look like this:
\image html dw-interrupted-drawing-1.png
Note the missing "Float, line 2/3" of element #fl-1, which is covered
by element #sc-2.
As described in \ref dw-out-of-flow, it has to be distinguished
between the *container* hierarchy (equivalent to the hierarchy of
dw::core::Widget.) and the the *generator* hierarchy. In the following
diagram, the former is represented by solid lines, the latter by
dotted lines:
\dot
digraph G {
node [shape=rect, fontname=Helvetica, fontsize=10];
edge [arrowhead="vee"];
"#sc-1" [fillcolor="#ffe0e0", style="filled"];
"#fl-1" [fillcolor="#b0ffb0", style="filled"];
"#sc-2" [fillcolor="#f0f0ff", style="filled"];
"body" -> "#sc-1";
"body" -> "#fl-1";
{ rank=same; "#sc-1" -> "#fl-1" [style=dotted]; }
"#sc-1" -> "#sc-2";
}
\enddot
The drawing order of the four elements (represented by widgets) is:
- body,
- #sc-1,
- #fl-1,
- #sc-2.
Since
1. #sc-2 is a child of #sc-1, but
2. #fl-1 is a child of the body, and
3. a widget can only draw its descendants (not necessary children,
but drawing siblings is not allowed),
#sc-1 cannot be drawn as a whole; instead drawing is **interrupted**
by #fl-1. This means:
1. the background and text of #sc-1 is drawn;
2. drawing of #sc-1 is **interrupted** by #fl-1 (see below for details),
3. drawing of #sc-1 is **continued**, by drawing #sc-2.
The exact control flow is described in this sequence diagram:
\image html dw-interrupted-drawing-2.png
When is drawing interrupted?
============================
A widget out of flow is regarded as part of the stacking context (see
\ref dw-stacking-context) of its *generator* (in the example above:
#fl-1 is part of the stacking context stablished by #sc-1, not the one
established by body). For this reason, a widget out of flow must, in
some cases, drawn while the *gerator* is drawn, as an
interruption. The exact rule:
A widget out of flow must be drawn as an interruption (while the
*generator* is drawn) if the stacking context of the generator (to
which this widget belongs) is in front of the stacking context of the
container (the parent widget).
See dw::oof::OOFAwareWidget::doesWidgetOOFInterruptDrawing.
How does interruption of drawing work?
======================================
When a widget detects that an other widget should be drawn as
interruption (see above), it calls dw::core::Widget::drawInterruption,
which
1. draws the widget within another "context" (area and reference
widget); for this the original drawing area
(dw::core::DrawingContext::getToplevelArea) is used.
2. Using dw::core::DrawingContext::addWidgetDrawnAsInterruption, and
checking later with
dw::core::DrawingContext::hasWidgetBeenDrawnAsInterruption prevents
these widgets from being drawn twice.
*/