1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
|
/** \page dw-interrupted-drawing Interrupted drawing
Describing the problem
======================
Without interrupting drawing (which is described below), a widget can
define the order in which its parts (background, non-widget content,
child widgets, etc.) are drawn, but it must be drawn as a whole. There
are situations when this is not possible.
Consider the following simple HTML document:
<head>
<style>
#sc-1 { position: relative; z-index: 1; background: #ffe0e0; }
#fl-1 { float: right; background: #b0ffb0; }
#sc-2 { position: relative; z-index: 1; background: #f0f0ff; }
</style>
</head>
<body>
<div id="sc-1">
<div id="fl-1">
Float, line 1/3<br/>
Float, line 2/3<br/>
Float, line 3/3
</div>
Stacking Context 1
<div id="sc-2">Stacking Context 2</div>
</div>
</body>
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 neccessary 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.
*/
|
