pre-capture lock screen screenshots via hidden window and ScreenshotService

shell/services/ScreenshotService.qml

@@ -0,0 +1,44 @@
+pragma Singleton
+
+import QtQuick
+
+QtObject {
+    id: root
+
+    // Screen name -> in-memory image URL from grabToImage
+    property var screenshots: ({})
+    property int _pending: 0
+
+    // Keep references to prevent garbage collection of the image data
+    property var _results: ({})
+
+    signal captureRequested
+    signal captureComplete
+
+    function capture(screenCount) {
+        _pending = screenCount;
+        if (_pending === 0) {
+            captureComplete();
+            return;
+        }
+        captureRequested();
+    }
+
+    function store(screenName, result) {
+        const s = Object.assign({}, screenshots);
+        s[screenName] = result.url;
+        screenshots = s;
+
+        const r = Object.assign({}, _results);
+        r[screenName] = result;
+        _results = r;
+
+        _pending--;
+        if (_pending <= 0)
+            captureComplete();
+    }
+
+    function get(screenName) {
+        return screenshots[screenName] || "";
+    }
+}