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KevinH · 08-02-2021, 11:27 AM

Okay, this is really messy. It seems a call to setZoomFactor for a QWebEngineView does not complete instantaneously nor is it immediately reflected in the internal state of the QWebEngineView after the call returns.

So any attempt to immediately scroll and centre the Preview Window on a location fails as the window inner height returned by javascript is incorrect for zoom values different from 100% until the zoom is done completely.

The interface for setZoomFactor is not designed to be asynchronous and so there is no way I know about to check if the zoom is complete yet (ie. to wait until setZoomFactor has completed and be reflected inside the QWebEngineView).

To make the situation worse, anytime a page is loaded, its internal zoom value is seemingly set back to 100%, requiring us to use setZoomFactor each time and then wait some amount of time before trying to scroll.

So a delay is needed between the call to Zoom (setZoomFactor) and when we try to scroll to a location. Among a bunch of other changes needed, I have tried to add that delay in PreviewWindow.cpp.

So right now, a delay of 50ms seems to be sufficient when set in DelayedScrollTo by a singleshot in PreviewWindow.cpp once the zoom is done. I have no way to know if that is enough for all platforms. I tried with a delay of 30ms and it fails.

I have pushed this approach to master. So we need people who can pull and build on Windows and Linux to see if this approach can be made workable for all platforms so that Preview syncing when Preview is not set to 100% works.

Please let me know what you find if you do get a chance to play around with this test case.

08-02-2021, 11:27 AM	#32
KevinH Sigil Developer Posts: 8,915 Karma: 6120478 Join Date: Nov 2009 Device: many	Okay, this is really messy. It seems a call to setZoomFactor for a QWebEngineView does not complete instantaneously nor is it immediately reflected in the internal state of the QWebEngineView after the call returns. So any attempt to immediately scroll and centre the Preview Window on a location fails as the window inner height returned by javascript is incorrect for zoom values different from 100% until the zoom is done completely. The interface for setZoomFactor is not designed to be asynchronous and so there is no way I know about to check if the zoom is complete yet (ie. to wait until setZoomFactor has completed and be reflected inside the QWebEngineView). To make the situation worse, anytime a page is loaded, its internal zoom value is seemingly set back to 100%, requiring us to use setZoomFactor each time and then wait some amount of time before trying to scroll. So a delay is needed between the call to Zoom (setZoomFactor) and when we try to scroll to a location. Among a bunch of other changes needed, I have tried to add that delay in PreviewWindow.cpp. So right now, a delay of 50ms seems to be sufficient when set in DelayedScrollTo by a singleshot in PreviewWindow.cpp once the zoom is done. I have no way to know if that is enough for all platforms. I tried with a delay of 30ms and it fails. I have pushed this approach to master. So we need people who can pull and build on Windows and Linux to see if this approach can be made workable for all platforms so that Preview syncing when Preview is not set to 100% works. Please let me know what you find if you do get a chance to play around with this test case.