Height-For-Width layouts and widgets

[jamesdbrock]

Rudolf Cardinal appears to have a real solution for the Label layout problem.

https://stackoverflow.com/questions/14238138/heightforwidth-label

• Rewrite the layouts.
• The best approach I've found is to have layouts calculate their children's geometry assuming some sort of standard rectangle (Qt itself often starts with a 640x480 one when drafting a layout); offering height information based on this draft; then, when setGeometry() is called, if the resulting height (based on a potentially new width) doesn't match what the layout previously advertised, re-constraining by calling parent->setFixedHeight().
• This allows you to use arbitrary widgets, and HFW widgets only need to support hasHeightForWidth() and heightForWidth() to have the new layouts (and their parent widgets, and any ancestor layouts using this mechanism) adjust their height.
• It can lead to some redrawing, but often not too much, as it happens on a per-layout not per-widget basis.

I've put C++ code at http://egret.psychol.cam.ac.uk/code/2017_01_16_qt_height_for_width/ for the following layouts:

• BoxLayoutHfw, VBoxLayoutHfw, HBoxLayoutHfw -- replacements for QBoxLayout etc.
• GridLayoutHfw -- replacements for QGridLayout.
• FlowLayoutHfw -- replacement for Qt's FlowLayout (http://doc.qt.io/qt-5/qtwidgets-layouts-flowlayout-example.html).

and the following widgets:

• AspectRatioPixmapLabel -- image maintaining its aspect ratio;
• LabelWordWrapWide -- word-wrapping label that tries to use as much horizontal space before it word-wraps.
• VerticalScrollArea -- as its name suggests, a vertical scroll area, but one that supports height-for-width cleanly.

Those layout and widgets are at these paths

• https://github.com/ucam-department-of-psychiatry/camcops/tree/master/tablet_qt/widgets
• https://github.com/ucam-department-of-psychiatry/camcops/tree/master/tablet_qt/layouts

The CamCOPS authors have relicensed those layouts and widgets as LGPL ucam-department-of-psychiatry/camcops#340

So this would be a complete solution to Qt layout problem, but it would require a few steps.

1. Create a new repository cardinal-qtwidgets for Shiboken Python bindings to all of those layouts and widgets. LGPL license. Depends on Qt.
2. Create a new repository pyedifice-cardinal-elements for Edifice Base Elements for all of those layouts and widgets. Depends on Qt and cardinal-qtwidgets and pyedifice. LGPL license.

[jamesdbrock]

Would resolve #41