ZoneSpy

A standalone window thumbnail streaming utility, forked from the CropAndLock module of Microsoft PowerToys.

Unlike the original PowerToys module, ZoneSpy runs independently—no PowerToys installation required. It focuses exclusively on the thumbnail streaming mode with real-time DWM content projection and shared memory output for external AI/vision programs.

What's different from PowerToys CropAndLock

Feature	PowerToys CropAndLock	ZoneSpy
Runtime	Requires PowerToys runner	Standalone executable
Modes	Thumbnail, Reparent, Screenshot	Thumbnail only (simplified)
Shared memory streaming	❌	✓ Real-time frame data via ZoneSpy_FrameData_{id}
Python viewer	❌	✓ tools/stream-viewer.py — display all feeds in one window
Borderless windows	❌	✓ Draggable floating windows, no title bar, edge snapping
Aspect-ratio lock	❌	✓ Hold Shift while resizing to maintain content ratio
Click-Through	❌	✓ Toggle from tray menu, clicks pass through to windows behind
Auto-reconnect	❌	✓ Reconnects when source window is closed and reopened
Window snapping	❌	✓ Snap to screen edges and other ZoneSpy windows
System tray	Managed by PowerToys	✓ Built-in tray icon with Exit, Click-Through and auto-start
Auto-start	❌	✓ Launch at startup via tray menu
Hotkey management	Managed by PowerToys	✓ Self-registered via RegisterHotKey

Features

• Live window thumbnail: Select any region of any window and display it in an always-on-top floating window with real-time DWM content projection
• Shared memory streaming (ZoneSpy_FrameData_{id}): Each thumbnail window exposes its content as BGRA pixel data in a named shared memory buffer at up to ~30 fps, with a frame-ready event (ZoneSpy_FrameReady_{id}) for synchronization
• Python stream viewer: tools/stream-viewer.py connects to all active streams and displays them in a single OpenCV window
• Content-change detection: When monitored content is static, capture rate drops to ~2 fps and shared memory is not signaled—consumers aren't woken for unchanged frames
• Frame sequence guard: Shared memory frame count uses odd/even protocol—consumers can detect torn frames by checking parity
• Worker-thread capture: Frame capture runs on a dedicated thread, not the UI message loop; dragging and menu interactions are never blocked
• Resize dialog: Right-click any thumbnail window → "Resize..." to set exact width and height. Optional aspect-ratio lock (🔒) keeps proportions when editing one dimension
• Borderless & snapping: Cropped windows have no title bar—drag and snap to screen edges
• Aspect-ratio lock: Hold Shift while resizing to preserve the original content aspect ratio
• Auto-reconnect: When the source window is closed and reopened, the cropped window automatically reconnects within seconds
• Click-Through: Toggle from the tray menu or right-click menu to make mouse clicks pass through
• Always on top: Cropped windows stay above all other windows by default (toggleable per window: right-click → "Always on top")
• Auto-start: Enable from tray menu to launch at Windows boot
• Window state persistence: Cropped window positions are saved and restored across sessions

Shared Memory API

Each cropped window creates a named shared memory and a frame-ready event. Stream information is written to %LocalAppData%\ZoneSpy\streams.json.

{
  "streams": [
    {
      "id": 0,
      "name": "Untitled - Notepad (Cropped)",
      "width": 800, "height": 600,
      "shm": "ZoneSpy_FrameData_0",
      "evt": "ZoneSpy_FrameReady_0"
    }
  ]
}

FrameHeader (20 bytes, packed):

Offset	Type	Field
0	uint32	frameCount
4	uint64	timestamp (ms)
12	uint32	width
16	uint32	height
20+	BGRA pixels	width × height × 4 bytes

Python consumption example:

import mmap, struct, numpy as np, win32event

buf = mmap.mmap(-1, 3840*2160*4+20, tagname="ZoneSpy_FrameData_0")
evt = win32event.OpenEvent(win32event.SYNCHRONIZE, False, "ZoneSpy_FrameReady_0")

while True:
    win32event.WaitForSingleObject(evt, win32event.INFINITE)
    buf.seek(0)
    fc, ts, w, h = struct.unpack_from("<I Q I I", buf, 0)
    pixels = np.frombuffer(buf.read(w * h * 4), dtype=np.uint8).reshape(h, w, 4)
    # pixels is BGRA, ready for model inference

See tools/stream-viewer.py for a complete working example.

Hotkey

Hotkey	Mode
Win+Ctrl+Shift+T	Thumbnail crop

Press the hotkey while the target window is in focus, then click and drag to select the region.

Tray Menu

Right-click the tray icon:

• Click-Through — toggle mouse passthrough
• Launch at startup — auto-start with Windows
• Exit — quit ZoneSpy

Right-Click Menu (per window)

Right-click any ZoneSpy thumbnail window:

• Always on top — toggle whether this window stays above others
• Resize... — open a dialog to set exact width and height (with optional aspect-ratio lock)
• Close — close this thumbnail

Building

Requires Visual Studio 2022+ (or 2026) and Windows 10 SDK.

.\tools\build\build.ps1 -Path src\modules\CropAndLock\CropAndLock -Platform x64 -Configuration Release

Pre-built binaries are available under the Actions tab.

License

MIT

ZoneSpy is based on the CropAndLock module from Microsoft PowerToys, licensed under the MIT License.