23033: Parts are displayed at incorrect zoom level when the Navigator is open

[krasko78]

Resolves: #23033

KEY POINTS:
Overview:

1. When the Navigator is open, it creates a NotationNavigator instance which inherits from AbstractNotationPaintView.

2. For the actual notation an instance of NotationPaintView is created which also inherits from AbstractNotationPaintView.

3. Both of these listen for current notation changes in AbstractNotationPaintView::onNotationSetup() (line 622) and call onCurrentNotationChanged() (line 623).

4. AbstractNotationPaintView::onCurrentNotationChanged() calls onLoadNotation (line 226).

5. onLoadNotation is supposed to call m_inputController->initZoom(); (line 232) where the zoom on the notation should be set (if not previously set) following these calls:

• NotationViewInputController::initZoom()
• NotationViewInputController::setZoom / doZoomToPageWidth / doZoomToWholePage etc.
• AbstractNotationPaintView::setScaling
• AbstractNotationPaintView::scale
• AbstractNotationPaintView::onMatrixChanged for the NotationNavigator instance or NotationPaintView::onMatrixChanged for the NotationPaintView instance (an override).

The problem is in that:

1. The zoom is actually set in NotationPaintView::onMatrixChanged when it calls notation()->viewState()->setMatrix (line 62).

2. The above steps execute first for the NotationNavigator instance since it registers to listen for onCurrentNotationChanged notification before the NotationPaintView instance registers itself.

3. When the steps execute for the NotationNavigator instance, the zoom won't be set but NotationViewInputController::initZoom() will set isMatrixInited on the notation's viewstate to true (line 171).

4. When the steps execute the second time for the NotationPaintView instance, onLoadNotation does not call m_inputController->initZoom() (line 232) because the if condition returns false due to isMatrixInited() being true for the notation.

5. The zoom of the notation remains unset and defaults to 0.

When the Navigator is not visible, the NotationNavigator instance is not created and does not interfere.

Further observations:
When the Navigator is active the two AbstractNotationPaintView descendants share the same notation. As a result the code in AbstractNotationPaintView::onLoadNotation that operates on the notation executes twice, e.g. event listeners are bound twice and the handlers are executed twice. Therefore those pieces of code should probably be moved elsewhere (not as part of this issue though).

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