Shape the window when there is no compositor

On Xfce with compositing off, X11 has no alpha to blend against, so the
transparent background came out as a black box around the cat.

When a window comes up without an alpha channel, TNCat now cuts the window down
to the pixels the drawing covers, using the X11 shape extension, and refreshes
that 15 times a second so it follows the animation. A sitting cat in a 120 x 106
window comes out as 96 rectangles over 29 percent of the window, so most of the
box is gone. Edges are harder than with a compositor, one bit per pixel, and the
log says so and names the Xfce setting that gives smooth ones instead.

The image-to-rectangles step is platform independent and folds every device row
into its window row, which both halves the rectangle count on a scaled display
and keeps a pixel that is opaque in only one of them.

xcb and xcb-shape are picked up through pkg-config on Unix and the build still
works without them. Opaque mode now paints a neutral card rather than the coat
colour.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

qml/CatWindow.qml

@@ -17,7 +17,9 @@ Window {
     height: Math.round(width * sprite.implicitHeight / sprite.implicitWidth)
     x: cat.x
     y: Screen.desktopAvailableHeight - height - settings.bottomMargin
-    color: Platform.opaqueBackground ? settings.coat : "transparent"
+    // A neutral card reads better than the coat colour when the background
+    // cannot be transparent at all.
+    color: Platform.opaqueBackground ? "#f2f0ec" : "transparent"
     flags: Qt.FramelessWindowHint | Qt.WindowStaysOnTopHint | Qt.Tool
            | Qt.NoDropShadowWindowHint | Qt.WindowDoesNotAcceptFocus
            | (Platform.bypassWindowManager ? Qt.X11BypassWindowManagerHint : 0)
@@ -48,6 +50,17 @@ Window {
     }
     Screen.onDesktopAvailableWidthChanged: cat.stageWidth = Screen.desktopAvailableWidth
 
+    // Without a compositor the window is cut to the cat's own outline. The
+    // drawing animates, so the shape has to be refreshed; 15 Hz is enough for
+    // a swinging leg and cheap enough for a window this small.
+    Timer {
+        interval: 66
+        repeat: true
+        running: Platform.shapeWindows && win.visible
+        triggeredOnStart: true
+        onTriggered: Platform.updateWindowShape(win)
+    }
+
     // The eyes need to know where the face sits on the desktop.
     Binding {
         target: win.cat

qml/ChipWindow.qml

@@ -27,6 +27,14 @@ Window {
         NumberAnimation { duration: 320; easing.type: Easing.OutQuad }
     }
 
+    Timer {
+        interval: 66
+        repeat: true
+        running: Platform.shapeWindows && win.visible
+        triggeredOnStart: true
+        onTriggered: Platform.updateWindowShape(win)
+    }
+
     Chip {
         id: curl
         anchors.fill: parent

qml/CupWindow.qml

@@ -22,6 +22,14 @@ Window {
            | (Platform.bypassWindowManager ? Qt.X11BypassWindowManagerHint : 0)
     visible: cat.cupVisible
 
+    Timer {
+        interval: 66
+        repeat: true
+        running: Platform.shapeWindows && win.visible
+        triggeredOnStart: true
+        onTriggered: Platform.updateWindowShape(win)
+    }
+
     Cup {
         id: mug
         anchors.fill: parent