RFR: 8211294: ScrollPane content is blurry with 125% scaling

[Kevin Rushforth]

On Thu, 17 Dec 2020 17:46:28 GMT, Frederic Thevenet <fthevenet at openjdk.org> wrote:

>> Good point. We would need some way to invalidate the cached values if the screen scale changes.
>> 
>>> We could possibly listen to `Window::renderScaleXProperty` and `Window::renderScaleYProperty` and call `updateSnappedInsets` & `requestLayout` when one changes?
>> 
>> A layout will happen anyway as the result of a Window moving to another screen, so really it's only the cached snapped insets that need to be recalculated. I don't know whether a listener is the best approach, since it would need to handle the case where the Window changes (either because the scene changed or the scene was added to a new window), which would present similar challenges to what we face with treeVisible.
>> 
>> Another possibility is for `updateSnappedInsets` to also cache the scaleX/Y at which the snapped insets were computed. The `snappedXXXXX` methods could check the current scale against the cached scale (a simple == test) and call `updateSnappedInsets` if the scale changes.
>
> I've opted for the cache and check for screen scale solution, as I agree it presents less risks of leaked or missing listeners down the road.
> There's a slight unexpected drawback I've noticed, though, which is that the repaint for the affected Region does not seem to occur right away on moving the window to another screen, but only once the Region is interacted with (e.g. hovering the mouse over it).

Your latest patch looks exactly like what I would expect. I need to do some multi-screen testing on Windows with different scale factors.

> ... the repaint for the affected Region does not seem to occur right away on moving the window to another screen, but only once the Region is interacted with (e.g. hovering the mouse over it).

This seems like a different (and preexisting) bug then. I think we're up to three follow-on issues if I haven't lost track:

1. Rendering a cached node doesn't match rendering it directly even when the transform is unchanged.
2. TextFlow: methods copied from Region have not picked up subsequent changes in those methods
3. Need to Render and layout scene out when scale changes (either when moving to a screen with a different scale or when the scale changes as the result of changing the setting of the current screen)

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PR: https://git.openjdk.java.net/jfx/pull/308