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/** \page dw-size-request-pos Size requisitions depending on positions
<div style="border: 2px solid #ffff00; margin: 1em 0;
padding: 0.5em 1em; background-color: #ffffe0">The complex "widget
sizes" is currently divided into three documents: \ref
dw-widget-sizes, \ref dw-grows, and **Size requisitions depending on
positions** (this document).</div>
Motivation
==========
As described in \ref dw-out-of-flow (*The sizeRequest/sizeAllocate
problem*), the principle that the size of a widget depends only on the
sizes of its children causes some problems with floats; the current
solution is a frequent correction by calling
dw::core::Widget::queueResize. In this document, an alternative
approach is presented.
<div style="border: 2px solid #ffff00; margin: 1em 0; padding: 0.5em 1em;
background-color: #ffffe0">This approach works very well for floats, but not
for positioned elements, which means that calling
dw::core::Widget::queueResize is still needed for the latter. On the other
hand, dw::oof::OOFFloatsMgr (which is much more complex than
dw::oof::OOFPositionedMgr) can be simplified quite much.</div>
General Idea
============
A widget size may depend on the position relative to an anchestor
widget. If a widget wants to get the size of a child widget, it should
1. call the new methods dw::core::Widget::numSizeRequestReferences and
dw::core::Widget::sizeRequestReference, which return all widgets
relative to which the child's position must be calculated;
2. call dw::core::Widget::sizeRequest with the positions relative to
these widgets.
<div style="border: 2px solid #ffff00; margin: 1em 0;
padding: 0.5em 1em; background-color: #ffffe0">It is not sufficient
to work with *absolute* positions, since there may be an
interruption passing the positions so that absolute positions are
often not known.</div>
All positions passed to dw::core::Widget::sizeRequest must constitute
the position at which this child will be allocated.
There are situations where the parent widget is unable to determine
these positions before the size is known. An example: a textblock
widget cannot determine the positions of an inline widget (like an
image, or an inline block) before the line is finished; on the other
hand, finishing the line depends on knowing the sizes of the inline
widgets.
This may result in a conflict, when the size of an inline widget
depends on positions. Generally, the only widget whose size depends on
positions is dw::Textblock (the size will depend on the positions
within its oof container, see \ref dw-out-of-flow), so this conflict
occurs with inline blocks.
This conflict is handled in different ways:
1. Fortunately, this case is irrelevat for floats: an inline blocks
constitute its own floats container, so that there is no dependance
on a position within another widget.
2. For positioned elements, this case is relevant, since an inline
block is in most cases not a container for positioned element. In
this case, a generator will call the methods
dw::oof::OutOfFlowMgr::tellIncompletePosition1 and
dw::oof::OutOfFlowMgr::tellIncompletePosition2, instead of
dw::oof::OutOfFlowMgr::tellPosition and
dw::oof::OutOfFlowMgr::tellPosition2, respectively. (Since this
case is irrelevant for floats,
dw::oof::OOFFloatsMgr::tellIncompletePosition1 and
dw::oof::OOFFloatsMgr::tellIncompletePosition2 are not implemented but
simply abort.)
(This is not (yet) considered for borders: borders are only relevant
for floats, but conflicts do not occur for floats.)
Extremes
--------
Extremes may depend on the position in an analogue way, see:
- dw::core::Widget::numGetExtremesReferences,
- dw::core::Widget::getExtremesReference, and
- dw::core::Widget::getExtremes.
Resizing
--------
Currently, the size of a widget has to be recalculated, when
1. it has called dw::core::Widget::queueResize, or
2. the size of a child widget has to be recalculated.
Since for this new approach, the size does not only depend on the size of the
children, the second condition must be modified. See beginning of
dw::core::Widget::sizeRequest.
An implementation may have to consider, this too, especially when implementing
incremental resizing (see \ref dw-widget-sizes); see
dw::Textblock::sizeRequestImpl as an example.
Regarding changes of the position is not sufficient. Consider this example,
where a float size changes as soon as the image is loaded:
\image html dw-size-request-pos-01.png
The second paragraph ("A longer paragraph" ...) stays at the same position, both
absolute and relative to the float container, but has to be rewrapped because of
the float. Instead, this is handled by dw::oof::OutOfFlowMgr::markSizeChange
(and likewise dw::oof::OutOfFlowMgr::markExtremesChange), which is called by the
implementation of `markSizeChange` (or `markExtremesChange`, respectively) of
the OOF container. (See also the end of the comment of dw::oof::OOFAwareWidget.)
Plan
====
1. General design (dw::core::Widget::sizeRequestReference, changes to
dw::core::Widget::sizeRequest). Completed.
2. Implementation for dw::Textblock. Completed.
3. Change interface of dw::oof::OutOfFlowMgr (this affects mostly only
comments). Completed.
Affects methods dw::oof::OutOfFlowMgr::tellPosition1,
dw::oof::OutOfFlowMgr::tellPosition2,
dw::oof::OutOfFlowMgr::getLeftBorder,
dw::oof::OutOfFlowMgr::getRightBorder,
dw::oof::OutOfFlowMgr::hasFloatLeft,
dw::oof::OutOfFlowMgr::hasFloatRight,
dw::oof::OutOfFlowMgr::getLeftFloatHeight, and
dw::oof::OutOfFlowMgr::getRightFloatHeight.
4. Apply step 3 to calls within dw::Textblock. Completed.
<b>Attention:</b> After this step, and before completing the next steps, the
code is inconsistend and so incorrect.
5. Implement step 3 for floats (affects dw::oof::OOFFloatsMgr). **MOSTLY
COMPLETED.**
6. Implement step 3 for positioned elements (affects only
dw::oof::OOFPositionedMgr). **INCOMPLETE.** (But positioned elements are
currently deactivated.)
Issues
======
- Since the signature of dw::core::Widget::sizeRequestImpl changes
quite often during the development of *size requisitions depending
on positions*, a simpler option dw::core::Widget::sizeRequestSimpl
has been added. May be removed again, after the design is stable.
- There may be inconsistencies for widget styles; see
[revision f797436687fe](http://flpsed.org/hgweb/dillo_grows/rev/f797436687fe)
as an example for a fix. Perhaps a different approach, where breaks are added,
_if `display` has the value `block`_ (or analogue), will work better.
*/
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