Add window detection capture with rounded corners

Hovering during selection now highlights the window under the cursor;
clicking captures it with a rounded-corner alpha mask matching macOS
window chrome. Dragging still switches to manual marquee selection.

💘 Generated with Crush

Assisted-by: Crush:deepseek-v4-flash-0731

Sources/Kapture/CaptureController.swift

@@ -59,13 +59,25 @@ final class CaptureController: NSObject {
             OverlayWindow(
                 screen: screen,
                 onComplete: { [weak self] rect in self?.finishSelection(rect) },
-                onCancel: { [weak self] in self?.cancelSelection() }
+                onCancel: { [weak self] in self?.cancelSelection() },
+                onWindowPick: { [weak self] rect in self?.finishWindowPick(rect) }
             )
         }
         overlays.forEach { $0.makeKeyAndOrderFront(nil) }
         overlayIDs = overlays.map { $0.windowNumber }
     }
 
+    /// A window was picked from hover — capture it with rounded corners.
+    private func finishWindowPick(_ rect: NSRect) {
+        let ids = overlayIDs
+        hideOverlays()
+        isSelecting = false
+        restorePreviousApp()
+        DispatchQueue.main.async { [self] in
+            capture(rect, excludingWindowIDs: ids, roundedCorners: true)
+        }
+    }
+
     private func finishSelection(_ rect: NSRect) {
         let ids = overlayIDs
         hideOverlays()
@@ -94,8 +106,8 @@ final class CaptureController: NSObject {
         previousApp = nil
     }
 
-    private func capture(_ rect: NSRect, excludingWindowIDs ids: [Int]) {
-        ScreenCapture.shared.capture(rect, excludingWindowIDs: ids) { [weak self] image in
+    private func capture(_ rect: NSRect, excludingWindowIDs ids: [Int], roundedCorners: Bool = false) {
+        ScreenCapture.shared.capture(rect, excludingWindowIDs: ids, roundedCorners: roundedCorners) { [weak self] image in
             DispatchQueue.main.async {
                 self?.isSelecting = false
                 self?.restorePreviousApp()
@@ -117,7 +129,7 @@ final class ScreenCapture {
     private init() {}
 
     @available(macOS 14.0, *)
-    private func crop(_ image: CGImage, to cgRect: CGRect, display: SCDisplay) -> CGImage? {
+    private func crop(_ image: CGImage, to cgRect: CGRect, display: SCDisplay, roundedCorners: Bool = false) -> CGImage? {
         // cgRect is in SCDisplay space (bottom-left origin, Y flipped vs AppKit).
         // The captured image has a TOP-LEFT origin. So within the display,
         // we must flip Y: pixelY = displayHeight - (cgY - displayMinY) - cgHeight.
@@ -141,7 +153,32 @@ final class ScreenCapture {
         // CGContext, which resamples and loses quality on retina captures.
         let rounded = safeRect.integral
         guard rounded.width >= 1, rounded.height >= 1 else { return nil }
-        return image.cropping(to: rounded)
+        guard var result = image.cropping(to: rounded) else { return nil }
+
+        // Apply a rounded-corner alpha mask for window captures, matching
+        // macOS window chrome (≈10pt radius, scaled to image pixels).
+        if roundedCorners {
+            let radius = 10 * scaleX
+            let maskRect = CGRect(x: 0, y: 0, width: result.width, height: result.height)
+            guard let maskCtx = CGContext(
+                data: nil, width: result.width, height: result.height,
+                bitsPerComponent: 8, bytesPerRow: 0,
+                space: CGColorSpaceCreateDeviceRGB(),
+                bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue
+            ) else { return result }
+            maskCtx.setFillColor(CGColor(gray: 1, alpha: 1))
+            maskCtx.fill(maskRect)
+            maskCtx.setBlendMode(.clear)
+            maskCtx.setFillColor(CGColor(gray: 0, alpha: 1))
+            maskCtx.addPath(CGPath(roundedRect: maskRect, cornerWidth: radius, cornerHeight: radius, transform: nil))
+            maskCtx.fillPath()
+            maskCtx.setBlendMode(.normal)
+            if let mask = maskCtx.makeImage(),
+               let masked = result.masking(mask) {
+                result = masked
+            }
+        }
+        return result
     }
 
     @available(macOS 14.0, *)
@@ -154,7 +191,7 @@ final class ScreenCapture {
         return content.displays.first(where: { $0.displayID == cgID }) ?? content.displays.first
     }
 
-    func capture(_ rect: NSRect, excludingWindowIDs excludedIDs: [Int], completion: @escaping (CGImage?) -> Void) {
+    func capture(_ rect: NSRect, excludingWindowIDs excludedIDs: [Int], roundedCorners: Bool = false, completion: @escaping (CGImage?) -> Void) {
         if #available(macOS 14.0, *) {
             Task {
                 guard let content = try? await SCShareableContent.current,
@@ -193,7 +230,7 @@ final class ScreenCapture {
                     completion(nil)
                     return
                 }
-                completion(self.crop(image, to: scRect, display: display))
+                completion(self.crop(image, to: scRect, display: display, roundedCorners: roundedCorners))
             }
         } else {
             guard let primary = NSScreen.screens.first(where: { $0.frame.origin == .zero }) ?? NSScreen.screens.first else {