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Bug 4670 - Monitor DPI transition on latest Windows 10 causes infinite window growth
Summary: Monitor DPI transition on latest Windows 10 causes infinite window growth
Status: WAITING
Alias: None
Product: SDL
Classification: Unclassified
Component: events (show other bugs)
Version: HG 2.1
Hardware: x86 Windows 10
: P2 major
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2019-06-17 21:04 UTC by Katelyn Gadd
Modified: 2019-06-18 06:17 UTC (History)
0 users

See Also:

Attachments
before (ideal resolution, on 150% dpi monitor) (253.93 KB, image/png)
2019-06-17 21:04 UTC, Katelyn Gadd 		Details
After a few mousemove events on the 100% dpi monitor (253.77 KB, image/png)
2019-06-17 21:04 UTC, Katelyn Gadd 		Details
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Description Katelyn Gadd 2019-06-17 21:04:10 UTC 
Created attachment 3827 [details]
before (ideal resolution, on 150% dpi monitor)

If you enable the new 'permonitorv2' DPI awareness mode using an app manifest (app.manifest) in recent versions of Windows 10, SDL windows will grow infinitely on mousemove once they transition to a monitor with lower DPI. I'll attach two comparison screenshots.

I wasn't able to build a reduced repro yet, but from what I can tell the problem is that V2 scales non-client portions of the window and SDL appears to use integer pixels for non client and client size calculations. If the base windows DPI is say 150% (like my 4k monitor) and the window transitions to a 100% DPI window, the values are no longer integral pixel counts and as a result SDL produces rounding errors. When that happens every mouse move causes large vertical growth (because the titlebar is big) and slow horizontal growth. Moving back to the original monitor stops the growth but leaves the size incorrect.

Set component to events since it happens during mousemove event processing.
Comment 1 Katelyn Gadd 2019-06-17 21:04:28 UTC 
Created attachment 3828 [details]
After a few mousemove events on the 100% dpi monitor
Comment 2 Sam Lantinga 2019-06-17 21:44:17 UTC 
Do you have a patch to fix this that we can include in SDL 2.0.10?

Thanks!
Comment 3 Katelyn Gadd 2019-06-18 06:17:52 UTC 
I honestly don't know SDL well enough to fix this. I could look into it some. Is there a particular SDL sample or testcase I should use to verify all the DPI-related stuff? I don't want to just end up fixing it for my scenario and breaking it for others.