library: Add libportal screenshot entry

src/Library/Library.blp

@@ -43,6 +43,10 @@ Adw.PreferencesWindow library {
       title: "User Interface";
     }
 
+    Adw.PreferencesGroup library_platform {
+      title: "Platform APIs";
+    }
+
     Adw.PreferencesGroup {
       vexpand: true;
       valign: end;

src/Library/demos/Screenshot/main.blp

@@ -0,0 +1,32 @@
+using Gtk 4.0;
+using Adw 1;
+
+Adw.StatusPage {
+  title: "Screenshot";
+  description: _("Take a picture of the screen");
+  margin-top: 48;
+
+  Box {
+    orientation: vertical;
+    halign: center;
+
+    Box {
+      Picture picture {}
+      margin-bottom: 12;
+      width-request: 256;
+      height-request: 256;
+    }
+
+    Button button {
+      label: _("Take Screenshot");
+      margin-bottom: 42;
+      halign: center;
+      styles ["suggested-action"]
+    }
+
+    LinkButton {
+      label: "API Reference";
+      uri: "https://libportal.org/method.Portal.take_screenshot.html";
+    }
+  }
+}

src/Library/demos/Screenshot/main.js

@@ -0,0 +1,48 @@
+import Xdp from "gi://Xdp";
+import XdpGtk from "gi://XdpGtk4";
+import Gio from "gi://Gio";
+import Adw from "gi://Adw";
+
+const portal = new Xdp.Portal();
+const parent = XdpGtk.parent_new_gtk(workbench.window);
+
+const button = workbench.builder.get_object("button");
+const picture = workbench.builder.get_object("picture");
+
+Gio._promisify(
+  Xdp.Portal.prototype,
+  "take_screenshot",
+  "take_screenshot_finish",
+);
+
+button.connect("clicked", () => {
+  takeScreenshot().catch(logError);
+});
+
+async function takeScreenshot() {
+  const flags = Xdp.ScreenshotFlags.NONE;
+
+  let uri;
+  try {
+    uri = await portal.take_screenshot(parent, flags, null);
+  } catch (err) {
+    showPermissionError();
+    return;
+  }
+
+  const file = Gio.File.new_for_uri(uri);
+  picture.set_file(file);
+}
+
+function showPermissionError() {
+  const dialog = new Adw.MessageDialog({
+    heading: "Permission Error",
+    body: "Ensure Screenshot permission is enabled in\nSettings → Apps → Workbench",
+    close_response: "ok",
+    modal: true,
+    transient_for: workbench.window,
+  });
+
+  dialog.add_response("ok", "OK");
+  dialog.present();
+}

src/Library/demos/Screenshot/main.json

@@ -0,0 +1,10 @@
+{
+  "name": "Screenshot",
+  "category": "platform",
+  "description": "Take a picture of the screen",
+  "panels": [
+    "code",
+    "preview"
+  ],
+  "autorun": true
+}