feat(grabandmove): snap windows to screen edges and corners while dragging

[James Martin (jjamesmartiin)]

Summary of the Pull Request

Adds release-to-edge window snapping to the GrabAndMove utility. When dragging windows using the modifier key (Alt/Win + Left Click), dragging near the left or right work-area edge previews and snaps the window to that screen half using direct window positioning. Dragging to a screen corner previews and snaps the window to that quarter, and dragging to the top work-area edge previews and maximizes the window.

PR Checklist

• Closes: Easy Window Dragging & Resizing #37124
• Communication: Discussed in issue comments.
• Tests: Manually validated drag-move, edge preview overlay, left/right half snap, corner quarter snap, maximize snap, and right-click resize.
• Localization: Added GrabAndMove_SnapToEdges.Header and GrabAndMove_SnapToEdges.Description to Resources.resw.
• Dev docs: N/A (module setting addition).
• New binaries: No new binaries added (integrated into existing PowerToys.GrabAndMove.exe).
• Documentation updated: Companion docs PR: Grab And Move: document edge/corner snapping MicrosoftDocs/windows-dev-docs#6104

Detailed Description of the Pull Request / Additional comments

Technical Implementation Details:

1. Edge Snapping Logic (src/modules/GrabAndMove/GrabAndMove/main.cpp):
   • Added ComputeSnapTarget() to calculate work-area boundaries (GetWorkAreaForPoint) and determine if the cursor is within SNAP_EDGE_THRESHOLD (24px) of an edge or corner. Corners are checked first so quadrants take priority over the half-screen/maximize edge zones.
   • When armed, the existing DWM overlay window (RepositionOverlay) expands to preview the half-screen, quarter-screen, or full-screen target region with zeroed margins.
   • On mouse release, if armed:
     • Half / Corner: Positions the dragged window directly via SetWindowPos() so its visible frame (DWM extended frame bounds) matches the previewed half/quarter region, accounting for the invisible resize borders.
     • Top Edge: Calls ShowWindow(g_dragTarget, SW_MAXIMIZE).
2. Settings UI Integration:
   • Added SnapToEdges (snapToEdges bool property, default true) to GrabAndMoveProperties.cs.
   • Added ViewModel binding in GrabAndMoveViewModel.cs and UI toggle switch in GrabAndMovePage.xaml.
   • Updated Resources.resw (en-us).

Validation Steps Performed

1. Standalone GrabAndMove Execution:
   • Executed PowerToys.GrabAndMove.exe with explorer PID runner parameter.
2. Window Movement & Snapping:
   • Held Alt + left-click drag on target windows (e.g. Notepad, Edge, Command Prompt).
   • Dragged cursor to left work-area edge -> Gold preview overlay rendered on left half of monitor -> Released mouse -> Window snapped to left half.
   • Dragged cursor to right work-area edge -> Overlay rendered on right half -> Released mouse -> Window snapped to right half.
   • Dragged cursor to top work-area edge -> Overlay rendered on entire work area -> Released mouse -> Window maximized.
   • Dragged cursor to each screen corner -> Overlay rendered on that quarter -> Released mouse -> Window snapped to that quarter.
3. Settings UI Validation:
   • Toggled "Snap windows to screen edges while dragging" off -> Dragging to edges showed standard window outline without triggering snap.
   • Toggled on -> Edge snap functionality restored.
4. Regression Check:
   • Confirmed Alt + Right-Click window resize operations function normally without interference.

Video Demonstration

power-toys-grab-and-move-snapping-demo-10mb.mp4

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[James Martin (jjamesmartiin)]

@microsoft-github-policy-service agree

[James Martin (jjamesmartiin)]

📷 Visual Evidence & UI Summary

As requested by the PR intake bot check, here is the visual breakdown for the UI additions in GrabAndMovePage.xaml:

1. Settings UI Integration (GrabAndMovePage.xaml & Resources.resw)

• Toggle Switch: Added Snap windows to screen edges while dragging (SnapToEdges, default true).
• Header: Snap windows to screen edges while dragging
• Description: Release a dragged window near the left or right edge to snap it to that half, or near the top edge to maximize it

2. Edge Snapping Overlay Behavior

• Left / Right Edge: Dragging within 16px of the left or right work-area edge displays the DWM target overlay across that half of the screen; releasing sends synthetic Win + Left / Win + Right to trigger native Aero Snap.
• Top Edge: Dragging near the top work-area edge displays a full work-area overlay; releasing calls ShowWindow(..., SW_MAXIMIZE).

1/4 Snap

1/2 Snap

Full-screen

[James Martin (jjamesmartiin)]

Hi! I've put together a short (~30 second) screen recording that walks through the snapping behavior end-to-end: the new Settings toggle, snapping to a half at the left/right edge, snapping to a quarter at the corners, and maximizing at the top edge. Please let me know if there's anything else you'd like me to include or if you have any feedback on the behavior or the settings wording — happy to make changes. Thanks for taking a look!

power-toys-grab-and-move-snapping-demo-10mb.mp4

[James Martin (jjamesmartiin)]

Quick note: I ran clang-format against main.cpp (per the repo's .clang-format) to make sure the new edge/corner snapping code matches the style guide. Purely formatting — no behavior changes — and Debug + Release builds are both clean.