Win11 Hdf5TreeView: gui.hdf5.Hdf5Item: cache expensive qt.QApplication.style().standardIcon() lookups

[tifuchs]

Addresses #4485

PR summary

Fixes Hdf5TreeView slowness on Win 11 caused by slow qt.QApplication.style().standardIcon(icon) calls in gui.hdf5.Hdf5Item.

This PR just adds simple caching of the icons in a dict.

The scaling factor of the primary screen is added as key to the icon cache. This should account for multi-monitor setups with different DPI scaling. - Works on my two screens.

There is a related issue addressing silx icon caching, which causes Exceptions when leaving silx
#1771

But I haven't encountered this issue with the simple dict solution.

pytests fail on my machine with a probably unrelated issue:

tmp_path = WindowsPath('C:/Users/timof/AppData/Local/Temp/pytest-of-timof/pytest-0/testErrorInInsertFilenameAsync0')
caplog = <_pytest.logging.LogCaptureFixture object at 0x00000246CAEE6900>
qapp_utils = <silx.gui.utils.testutils.TestCaseQt testMethod=runTest>

    def testErrorInInsertFilenameAsync(tmp_path, caplog, qapp_utils):
        filename = str(tmp_path / "corrupt.h5")
        with open(filename, "wb") as h5file:
            h5file.write("8736553".encode())

        model = hdf5.Hdf5TreeModel()
        assert model.rowCount(qt.QModelIndex()) == 0
        model.insertFileAsync(filename)

        assert qt.silxGlobalThreadPool().waitForDone(2000)  # Needed for PySide6
>       waitForPendingOperations(qapp_utils, model)

test\test_hdf5.py:85:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

qapp_utils = <silx.gui.utils.testutils.TestCaseQt testMethod=runTest>
model = <silx.gui.hdf5.Hdf5TreeModel.Hdf5TreeModel(0x246c59908c0) at 0x00000246CB5F9E00>

    def waitForPendingOperations(qapp_utils: TestCaseQt, model):
        for _ in range(20):
            if not model.hasPendingOperations():
                break
            qapp_utils.qWait(200)
        else:
>           raise RuntimeError("Still waiting for a pending operation")
E           RuntimeError: Still waiting for a pending operation

AI Disclosure

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[t20100]

Thanks for looking into this and for proposing a fix!
This is unfortunate qt does not cache standard icons.

Just one comment: the cache key could be simplified.

[t20100]

devicePixelRatio shouldn't be needed in the cache key: the QIcon contains multiple-size pixmaps so there is no need to change it with devicePixelRatio.

Suggested change

	devicePixelRatio = None
	app = qt.QApplication.instance()
	if app is not None:
	screen = app.primaryScreen()
	if screen is not None:
	devicePixelRatio = screen.devicePixelRatio()
	key = style.objectName(), devicePixelRatio, icon
	key = style.objectName(), icon

BTW, if devicePixelRatio is needed, best to use QWindow.devicePixelRatio (see https://doc.qt.io/qt-6/qscreen.html#devicePixelRatio-prop)

[tifuchs]

You are correct, I have confirmed that QIcon returns differently sized icons. However, depending on QT_SCALE_FACTOR, the size is scaled for some icons, (used QIcon.availableSizes() to check it):

QT_SCALE_FACTOR = 1 : SP_DirIcon: QSize(100, 100) ... QSize(1600, 1600)

QT_SCALE_FACTOR = 2 : SP_DirIcon : QSize(200, 200) ... QSize(3200, 3200)

But the behavior is not really consistent. For example SP_DialogOkButton
does not get scaled (16, 16) -> (128, 128) independent of QT_SCALE_FACTOR.

Thus, devicePixelRatio might still be required. Though, QIcon has a built-in scaling feature. So it might not make a big difference.
I think we could remove it. Let me know.

style.objectName() is something like windowsvista, win11, ...
Do we expect this to change during runtime? - Could also be removed.

[tifuchs]

I reverted it back to a minimal working version.

This version does not account for style changes. And also not for full scaling (High DPI) changes.

I think this would still be fine, if we accept that:

1. We don't account for the user to change the visual style at runtime. I think that this is a good assumption.
2. Even though the size of stored QIcon changes depending on QT_SCALE_FACTOR, QIcon does store multiple versions and will display an icon in any case (presumably with lower quality). This issue only exists on multi-screen setups.

https://doc.qt.io/qt-6/qicon.html#pixmap
The pixmap might be smaller than requested, but never larger, unless the device-pixel ratio of the returned pixmap is larger than 1.
So the returned pixmaps might be smaller if the QIcon was created on a low DPI screen and then the screen is changed to a high DPI screen.

[t20100]

LGTM, thanks for the fix!

From what I tested on Linux with PySide6, icons behaves correctly when moving the window on different screens with different resolutions and changing screen display ratio.