Higher DPI effects magnifier performance

[Qchristensen]

Is your feature request related to a problem? Please describe.

Changing the windows DPI to higher than default affects mouse magnifier performance.
Note that this doesn't happen in narrator

Describe the solution you'd like

Panning following the mouse should be smooth.

Describe alternatives you've considered

No response

Additional context

Tested with nvda_snapshot_alpha-55570,bcd5eb66.exe

on Windows 11 (64-bit) Version: 25H2, Build: 26200.8246

The more I switch between NVDA and Windows magnifiers to try to document this, it's not always easy to document, but being used to one and then moving to the other, it is perceptible.

It is perhaps more prominent when other things are processing?

One other way to demonstrate it is to quickly yank the mouse sideways. While the mouse moves quickly even without any magnification running - with the Windows magnifier, the view pans quickly across to follow the mouse in real time. NVDA magnifier pauses a moment, then jumps across to the new location. As a user, there probably isn't as much practical difference in the time it takes to orient to the new location and read, but it FEELS jerkier and so it takes longer to adjust. Even that very small and fast amount of movement you notice with Windows magnifier does reinforce which way things are moving, so when they stop it doesn't seem as much of a "blink" to the new location.

[seanbudd]

This was caused by a higher DPI

[CyrilleB79]

See also #20060, which may be considered duplicate, but with a different scenario, video demonstrations and no higher dpi settings (scale = 100%).

[CyrilleB79]

It's worth noting that when you set Full screen mode = Center in NVDA Magnifier, you can still view the mouse cursor move a bit around its center position. On the opposite, during mouse mouvements with Windows Magnifier, the mouse cursor remains steady centered on the screen and the magnified view is just panned in the opposite direction as the mouse cursor move; this makes the mouse movements much smoother.

[CyrilleB79]

Another thing to note is that with Windows Magnifier, the reaction is not the same depending on whether the view follows the mouse cursor or the text cursor:

• when Windows Magnifier follows the mouse cursor, the reaction is immediate so that one cannot even see the mouse cursor move away from the screen center (if the center option is selected)
• when Windows Magnifier follows the text caret (and caret centered option is selected), there is a slight delay and a smooth update, maybe during half a second, as described in NVDA Magnifier - Moving the view should be smoother #20060, so that the eye can easily see what has been written or how the text cursor has moved before the caret is centered again.

For now, NVDA magnifier does not do this difference. But if the current issue is resolved, I think that such a difference should also be implemented in NVDA between text caret update and mouse update.

[hwf1324]

I noticed something: when moving, the Windows Magnifier is the most stable by comparison. The NVDA Magnifier is also relatively smooth when moving over the NVDA GUI (i.e., MFC), but there is noticeable lagging when moving over applications like Firefox.

I have only configured "Follow mouse" and "True center".

[CyrilleB79]

@seanbudd you write in #20396 (comment):

The issue #19987 was particularly about a change in smoothness due to setting a higher DPI.

It's not obvious to me reading the initial description. Have you had other inputs, e.g. privately, from @Qchristensen?

In any case, does it mean that the current issue does not cover #19987 (comment), i.e. the mouse cursor not remaining steady centred in the view while moving around? (on opposite to Windows Magnifier) Do I need to open a separate issue for this?