put shell in subdir, and add nix package

shell/screencapture/SelectionRectangle.qml

@@ -0,0 +1,54 @@
+import QtQuick
+import ".."
+
+Canvas {
+    id: root
+
+    property color overlayColor: "#80000000"
+    property color outlineColor: ShellSettings.colors["primary"]
+    property rect selectionRect
+    property point startPosition
+    signal areaSelected(rect selection)
+
+    onPaint: {
+        var ctx = getContext("2d");
+        ctx.clearRect(0, 0, width, height);
+
+        // grey overlay
+        ctx.fillStyle = overlayColor;
+        ctx.fillRect(0, 0, width, height);
+
+        // cut out the selection rectangle
+        ctx.globalCompositeOperation = "destination-out";
+        ctx.fillRect(selectionRect.x, selectionRect.y, selectionRect.width, selectionRect.height);
+        ctx.globalCompositeOperation = "source-over";
+        ctx.strokeStyle = outlineColor; 
+        ctx.lineWidth = 2; 
+        ctx.strokeRect(selectionRect.x, selectionRect.y, selectionRect.width, selectionRect.height);
+    }
+
+    MouseArea {
+        anchors.fill: parent
+
+        onPressed: mouse => {
+            root.startPosition = Qt.point(mouse.x, mouse.y);
+        }
+
+        onPositionChanged: mouse => {
+            if (pressed) {
+                var x = Math.min(root.startPosition.x, mouse.x);
+                var y = Math.min(root.startPosition.y, mouse.y);
+                var width = Math.abs(mouse.x - root.startPosition.x);
+                var height = Math.abs(mouse.y - root.startPosition.y);
+
+                root.selectionRect = Qt.rect(x, y, width, height);
+                root.requestPaint();
+            }
+        }
+
+        onReleased: mouse => {
+            root.visible = false;
+            root.areaSelected(root.selectionRect);
+        }
+    }
+}