capture-screen

# Capture Screen Programmatic screenshot capture on macOS: find windows, control views, capture images. ## Select observation or foreground control For an existing view, enumerate and capture the exact window without activating it. Skip Step 2 when no view change is needed. A window image proves visible content in that capture, not keyboard focus, input delivery or a successful business action. Before opening/raising windows, scrolling, selecting, changing zoom or sending keys, the executing agent checks user activity and other agents' ownership. Use a concrete task handoff or an existing explicit idle-desktop authorization; under the latter, coordinate exclusive access and proceed without asking again. Idle input alone is not ownership. Busy/unknown occupancy or unexpected input stops foreground actions; continue independent reads and do not restore old focus after human takeover. Inspect the chosen tool's activation semantics. An app-targeted call or a shell job running in the background does not prove it preserves focus. A failed capture does not authorize raising the window, permission changes or switching tools around a host refusal/GUI lock. Only request a handoff when existing authorization is absent. ## Quick Start ### Observe an unidentified dialog or the full desktop Use this route when the user requests a whole-screen view, or when permitted window observation cannot identify the reported obstruction. First establish that the host permits this capture and its scope. An app-specific control refusal does not prove screen capture is unavailable; it also does not authorize using a different tool to read content the host protects. Stop if the refusal covers the proposed capture or a GUI lock prevents it. Capture without activation, scrolling or input: ```bash capture_dir="$(mktemp -d)" screencapture -x "$capture_dir/desktop.png" ``` Inspect the resulting image with the host's permitted image viewer. On a multi-display desktop, inspect each produced display image before claiming to have checked the whole desktop. File creation alone does not prove the requested dialog was captured. Once identified, prefer the exact window for further observations and keep the user's reported interaction failure in scope. Follow the macOS permission owner's `macos-permissions` entry for classification and recovery. ### Capture a known window ```bash # Find Excel window ID swift scripts/get_window_id.swift Excel # Capture that window (replace 12345 with actual WID) screencapture -x -l 12345 output.png ``` ## Step 1: Get Window ID (Swift) Use the bundled Swift/CoreGraphics route when the host permits window enumeration. Prefer the host's native window inventory when it supplies the required IDs. ### Quick inline execution ```bash swift -e ' import CoreGraphics let keyword = "Excel" let list = CGWindowListCopyWindowInfo(.optionOnScreenOnly, kCGNullWindowID) as? [[String: Any]] ?? [] for w in list { let owner = w[kCGWindowOwnerName as String] as? String ?? "" let name = w[kCGWindowName as String] as? String ?? "" let wid = w[kCGWindowNumber as String] as? Int ?? 0 if owner.localizedCaseInsensitiveContains(keyword) || name.localizedCaseInsensitiveContains(keyword) { print("WID=\(wid) | App=\(owner) | Title=\(name)") } } ' ``` ### Using the bundled script ```bash swift scripts/get_window_id.swift Excel swift scripts/get_window_id.swift Chrome swift scripts/get_window_id.swift # List all windows ``` Output format: `WID=12345 | App=Microsoft Excel | Title=workbook.xlsx` Parse the WID number for use with `screencapture -l`. ## Step 2: Control Window (AppleScript, optional foreground work) Use these commands only inside the authorized foreground interval above. Bind the exact app/window/document before using any `active window` or `active workbook` example; never infer the target from whichever window happens to be active. ### Microsoft Excel (full AppleScript support) ```bash # Activate (bring to front) osascript -e 'tell application "Microsoft Excel" to activate' # Set zoom level (percentage) osascript -e 'tell application "Microsoft Excel" set zoom of active window to 120 end tell' # Scroll to specific row osascript -e 'tell application "Microsoft Excel" set scroll row of active window to 45 end tell' # Scroll to specific column osascript -e 'tell application "Microsoft Excel" set scroll column of active window to 3 end tell' # Select a cell range osascript -e 'tell application "Microsoft Excel" select range "A1" of active sheet end tell' # Select a specific sheet osascript -e 'tell application "Microsoft Excel" activate object sheet "DCF" of active workbook end tell' # Open a file osascript -e 'tell application "Microsoft Excel" open POSIX file "/path/to/file.xlsx" end tell' ``` ### Any application (basic control) ```bash # Activate any app osascript -e 'tell application "Google Chrome" to activate' # Bring specific window to front (by index) osascript -e 'tell application "System Events" tell process "Google Chrome" perform action "AXRaise" of window 1 end tell end tell' ``` ### Timing and Timeout Always add `sleep 1` after AppleScript commands before capturing, to allow UI rendering to complete. **IMPORTANT**: `osascript` hangs indefinitely if the target application is not running or not responding. Always wrap with `timeout`: ```bash timeout 5 osascript -e 'tell application "Microsoft Excel" to activate' ``` ## Step 3: Capture (screencapture) ```bash # Capture specific window by ID screencapture -l <WID> output.png # Silent capture (no camera shutter sound) screencapture -x -l <WID> output.png # Capture as JPEG screencapture -l <WID> -t jpg output.jpg # Capture with delay (seconds) screencapture -l <WID> -T 2 output.png # Capture a screen region (interactive) screencapture -R x,y,width,height output.png ``` ### Retina displays On Retina Macs, `screencapture` outputs 2x resolution by default (e.g., a 2032x1238 window produces a 4064x2476 PNG). This is normal. To get 1x resolution, resize after capture: ```bash sips --resampleWidth 2032 output.png --out output_1x.png ``` ### Verify capture ```bash # Check file was created and has content ls -la output.png file output.png # Should show "PNG image data, ..." ``` ## Multi-Shot Workflow Foreground example: capture multiple sections of an Excel workbook. Establish the authorization and exclusive ownership above first. If a user takes over, stop the remaining sequence rather than replaying it or restoring your previous focus. ```bash # 1. Open file and activate Excel osascript -e 'tell application "Microsoft Excel" open POSIX file "/path/to/model.xlsx" activate end tell' sleep 2 # 2. Set up view osascript -e 'tell application "Microsoft Excel" set zoom of active window to 130 activate object sheet "Summary" of active workbook end tell' sleep 1 # 3. Get window ID # IMPORTANT: Always re-fetch before capturing. CGWindowID is invalidated # when an app restarts or a window is closed and reopened. WID=$(swift -e ' import CoreGraphics let list = CGWindowListCopyWindowInfo(.optionOnScreenOnly, kCGNullWindowID) as? [[String: Any]] ?? [] for w in list { let owner = w[kCGWindowOwnerName as String] as? String ?? "" let wid = w[kCGWindowNumber as String] as? Int ?? 0 if owner == "Microsoft Excel" { print(wid); break } } ') echo "Window ID: $WID" # 4. Capture Section A (top of sheet) osascript -e 'tell application "Microsoft Excel" set scroll row of active window to 1 end tell' sleep 1 screencapture -x -l $WID section_a.png # 5. Capture Section B (further down) osascript -e 'tell application "Microsoft Excel" set scroll row of active window to 45 end tell' sleep 1 screencapture -x -l $WID section_b.png # 6. Switch sheet and capture osascript -e 'tell application "Microsoft Excel" activate object sheet "DCF" of active workbook set scroll row of active window to 1 end tell' sleep 1 screencapture -x -l $WID dcf_overview.png ``` ## Failed Approaches (DO NOT USE) These methods were tested and confirmed to fail on macOS: | Method | Error | Why It Fails | |--------|-------|-------------| | `System Events` → `id of window` | Error -1728 | System Events cannot access window IDs in the format screencapture needs | | Python `import Quartz` (PyObjC) | `ModuleNotFoundError` | PyObjC not installed in system Python; don't attempt to install it — use Swift instead | | `osascript` window id | Wrong format | Returns AppleScript window index, not CGWindowID needed by `screencapture -l` | ## Permission Troubleshooting If `get_window_id.swift` cannot enumerate windows or a required field is unavailable, read the actual result before attributing the failure to Screen Recording. Request the helper's diagnostic guidance without enumerating windows: ```bash swift scripts/get_window_id.swift --permission-hint screen swift scripts/get_window_id.swift --permission-hint microphone ``` Interpret that output with the [helper diagnostic procedure](references/permission-triage-template.md). The hint prints guidance and execution context; it does not check grant state or identify which process should receive a grant. Keep general TCC attribution, permission changes and request recovery with `macos-permissions`. ## Supported Applications | Application | Window ID | AppleScript Control | Notes | |------------|-----------|-------------------|-------| | Microsoft Excel | Swift | Full (zoom, scroll, select, activate sheet) | Best supported | | Google Chrome | Swift | Basic (activate, window management) | No scroll/zoom via AppleScript | | Other macOS apps | Swift or permitted host inventory | App-dependent | Capture requires host permission and a capturable surface | AppleScript control depth varies by application. Excel has the richest AppleScript dictionary. For apps with limited AppleScript, keyboard simulation via `System Events` is a foreground alternative only after the entry gate passes, not an automatic recovery from a failed background action.