Fix OverflowException in WindowChromeWorker._HandleNCHitTest when dragging across different-DPI monitors - #1997
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…gging across different-DPI monitors Dragging the preview window onto a monitor with a different DPI (e.g. a non-primary 4K display) crashed with an arithmetic overflow inside WPF's WindowChromeWorker hit-test. The crash was triggered on WM_NCHITTEST, whose DPI math can't be made safe from the outside, so: - Short-circuit WM_NCHITTEST to HTCLIENT in ViewerWindow, and restore window dragging by hand (WM_NCLBUTTONDOWN + HT CAPTION) on the title area. - Apply the WM_DPICHANGED suggested rect so the HWND and WPF geometry stay in sync as the window moves between monitors. - Opt into Per-Monitor V2 DPI awareness (SetProcessDpiAwarenessContext) with a V1 fallback. - Clamp MoveWindow coordinates/size and sanitize non-finite window size so a degenerate rect can never reach Win32/WPF. Fixes QL-Win#1996
Reviewer's GuideThe PR prevents the .NET Framework 4.6.2 WindowChrome WM_NCHITTEST overflow during cross-DPI monitor dragging by bypassing WPF hit-testing, restoring native title-bar dragging, synchronizing WM_DPICHANGED geometry, enabling Per-Monitor V2 DPI awareness with fallback, and sanitizing all window coordinates and sizes. Sequence diagram for cross-DPI viewer window draggingsequenceDiagram
actor User
participant ViewerWindow
participant WPF as WindowChromeWorker
participant Win32
participant Monitor
User->>ViewerWindow: TitleArea_MouseLeftButtonDown
ViewerWindow->>Win32: ReleaseCapture()
ViewerWindow->>Win32: SendMessage(WM_NCLBUTTONDOWN, HTCAPTION)
User->>Monitor: Drag window across DPI boundary
Monitor-->>ViewerWindow: WM_DPICHANGED(suggestedRect)
ViewerWindow->>Win32: MoveWindow(suggestedRect)
User->>ViewerWindow: Window message WM_NCHITTEST
ViewerWindow-->>WPF: HTCLIENT
Note over ViewerWindow,WPF: WPF WindowChrome hit-testing is bypassed
Flow diagram for safe viewer window geometryflowchart TD
Input["Requested window size and position"] --> Size["PositionWindow"]
Size --> Finite["FinitePositive"]
Finite --> Move["MoveWindow"]
Move --> Clamp["ToInt32Clamped"]
Clamp --> Rect["Clamped coordinates and minimum dimensions"]
Rect --> Win32["User32.MoveWindow"]
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Hey - I've found 1 issue
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Please address the comments from this code review:
## Individual Comments
### Comment 1
<location path="QuickLook/ViewerWindow.xaml.cs" line_range="222-226" />
<code_context>
+ // overflow is in WPF's own DPI math, so no condition on the window rect can reliably
+ // detect it). Dragging still works because the content panels use WM_NCLBUTTONDOWN(HT
+ // CAPTION) directly rather than relying on a hit test result.
+ if (msg == WM_NCHITTEST)
+ {
+ handled = true;
+ return new IntPtr(1); // HTCLIENT
+ }
+
+ if (msg == WM_DPICHANGED && lParam != IntPtr.Zero)
</code_context>
<issue_to_address>
**issue (bug_risk):** Returning HTCLIENT for every WM_NCHITTEST prevents WindowChrome from reporting resize hit-test zones such as HTLEFT, HTRIGHT, HTTOP, and HTBOTTOM. Because ViewerWindow remains configured with ResizeMode="CanResize", users can no longer resize the preview window through its borders.
**Triggers:** When the user attempts to resize the preview window from any border or corner.
**Suggested fix:** Handle only the problematic hit-test path, or implement the WindowChrome resize hit-test zones and initiate native resizing manually instead of returning HTCLIENT for every point.
</issue_to_address>Sourcery assessment
Approval pending. 1 finding to address first.
Blocking findings: QuickLook/ViewerWindow.xaml.cs:226
… WM_NCHITTEST Sourcery correctly flagged that returning HTCLIENT for every WM_NCHITTEST disabled the resize borders while ResizeMode=CanResize. Report HTLEFT/HTRIGHT/ HTTOP/HTBOTTOM and the corner zones at the window edges, and HTCLIENT elsewhere, still bypassing the WindowChrome hit-test that overflows during cross-DPI drags.
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Problem
Dragging the preview window onto a monitor with a different DPI — e.g. a non-primary 4K display — crashed QuickLook with:
This is the crash reported in #1996 (crashes when dragging the preview window on a non-primary monitor). It happens on any preview type — the trigger is the shared
ViewerWindow, not a specific plugin.Root cause
The overflow is raised by WPF (.NET Framework 4.6.2)
WindowChromeWorker._HandleNCHitTeston theWM_NCHITTESTmessage. I decompiled the installedPresentationFramework.dlland confirmed that_HitTestNcaandDpiHelper.DevicePixelsToLogical/DeviceRectToLogicalcontain no overflowable(int)casts — the bad arithmetic lives entirely inside WPF's per-window DPI math, which becomes inconsistent as the window is dragged onto a monitor with a different DPI. That inconsistency can't be corrected from the outside, so the safe fix is to avoid the offending hit-test entirely.Changes
ViewerWindow: answerWM_NCHITTESTwithHTCLIENTto bypass the overflowing WindowChrome hit-test, and restore window dragging manually (WM_NCLBUTTONDOWN+HT CAPTION) on the title area, sinceWindow.DragMove()depends on a hit-test result.ViewerWindow: apply theWM_DPICHANGEDsuggested rect so the HWND and WPF geometry stay in sync when the window moves between monitors.App/SHCore: opt into Per-Monitor V2 DPI awareness (SetProcessDpiAwarenessContext) with a V1 fallback.WindowHelper/ViewerWindow.Actions: clampMoveWindowcoordinates/size and sanitize non-finite window sizes so a degenerate rect can never reach Win32/WPF.Fixes #1996.
Summary by Sourcery
Prevent cross-monitor DPI changes from triggering WPF hit-test overflows in preview windows.
Bug Fixes:
Enhancements: