Dillo v3.1.1-119-g140d9ebd
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Size requisitions depending on positions
The complex "widget sizes" is currently divided into three documents: Sizes of Dillo Widgets, GROWS - Grand Redesign Of Widget Sizes, and Size requisitions depending on positions (this document).
Furthermore, there are some notes in Miscellaneous Notes on Dw.

Motivation

As described in Handling Elements 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.

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.

General Idea

A widget size may depend on the position relative to an ancestor 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.
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.

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 Handling Elements 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 block constitutes 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 elements. 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:

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 Sizes of Dillo Widgets); 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:

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.

    Attention: After this step, and before completing the next steps, the code is inconsistent 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