There are three commits presented but the second one, despite its smallness, is the most interesting one. I spent several hours on this and even now I'm not 100% sure whether I got the theme code right.

You might ask why I didn't change also kDDCHeckbox*, kDDRadiobutton* and kDDPopUp* as those also contain the idle/disabled pairs. The embarrassing answer is that a) it doesn't work (sudden flashing, missing parts of the widgets etc) and b) I didn't understand its code. So either:

• my analysis below is wrong
• those widgets do something special, maybe even something which are not supposed to do
• the buttons should do something special and they don't so that's why my change is working here

So I left those as they were and intensively tested the button and dropdown button, as those were the problematic ones in the launcher. If it ain't broke, don't fix it, right? Of course, I also played with all the dialogs so see any regressions. If you can think of a problematic scenario (involving having a button / widget which can get enabled/disabled in real time without Apply / opening a new dialog etc = without forcing a full redraw), please do let me know.

Content of the commit message for better visibility:

Until now, every (even the tiniest) widget's change of the enabled state
resulted in a redraw of a complete dialog. Why this was needed and how
it has been fixed requires a bit of explanation.

There are two buffers to render the widgets in: Backbuffer and Screen
(selected by ThemeEngine::drawToBackbuffer() and
ThemeEngine::drawToScreen() respectively, setting
VectorRenderer::_activeSurface). Then there are two layers/flags:
kDrawLayerBackground and kDrawLayerForeground
(selected in Dialog::drawDialog(), setting ThemeEngine::_layerToDraw).

When asked for a complete dialog rebuild in GuiManager::redraw()
(kRedrawCloseDialog, kRedrawFull) the widgets of every dialog,
regardless of their layer, are drawn into Backbuffer and then copied
into Screen.

When asked for a partial dialog rebuild (kRedrawOpenDialog,
kRedrawTopDialog) the widgets of the topmost dialog marked with
kDrawLayerBackground are drawn into Backbuffer, then copied into Screen
and finally the widgets marked with kDrawLayerForeground are drawn into
Screen only.

When redraw() is called just within the GuiManager's event loop the
widgets of the topmost dialog are drawn into Screen only. And this is
where the layers become important.

When rebuilding the dialog, it doesn't really matter which layer has
been defined for a widget: Backbuffer contains the ones with
kDrawLayerBackground and Screen will supply the rest with
kDrawLayerForeground, if needed. But which layer is taken into account
when calling Dialog::drawWidgets() ?

It is important to realize that the content of Backbuffer is
defined by the widget's initial state (idle or disabled): so Backbuffer
will contain either "idle color" or "disabled color" after dialog's
creation.

ThemeEngine::drawDD() does two checks:

1. if widget has kDrawLayerBackground set and _activeSurface is Screen, copy the widget from Backbuffer to Screen

2. if widget's layer is the same as _layerToDraw, draw the widget into _activeSurface

This is what happens in redraw(kRedrawDisabled) for kDrawLayerBackground widgets:

• Backbuffer contains an idle/disabled (depending on its initial state) rendition of the widget
• widget is copied from Backbuffer to Screen (1st check in drawDD())
• widget is not drawn into Screen as _layerToDraw is kDrawLayerForeground from the last redraw() (2nd check in drawDD())

Summary: when switching between idle/disabled state, widget's color is not updated.

This is what happens in redraw(kRedrawDisabled) for kDrawLayerForeground widgets:

• Backbuffer contains an idle/disabled (depending on its initial state) rendition of the widget
• widget is not copied from Backbuffer to Screen as widget has kDrawLayerForeground set (1st check in drawDD())
• widget is drawn into Screen as _layerToDraw is kDrawLayerForeground from the last redraw() (2nd check in drawDD())

Summary: when switching between idle/disabled state, widget's color is correctly updated and not restored from Backbuffer.

This is why hovering didn't require scheduleTopDialogRedraw():

• Backbuffer contains an idle [kDrawLayerBackground] rendition of the widget
• when highlighted [kDrawLayerForeground], widget is not copied from Backbuffer to Screen
• widget is drawn into Screen

Unhovering:

• Backbuffer contains an idle [kDrawLayerBackground] rendition of the widget
• when idle [kDrawLayerBackground], widget is copied from Backbuffer to Screen
• widget is not drawn into Screen

The key difference here is that highlighting can't be stored as initial
state. If every widget had to be enabled in dialog redraw, only the
"disabled" widgets would had to be set to kDrawLayerForeground.