feat(notifications): window border on the balloons

The balloons now wear the Hyprland window border: 2px, the udt gradient
read from ~/.cache/udt/udt-border.lua (the file look_and_feel.lua reads,
watched so a wallpaper change follows), rotating, with the windows'
corners.

A Rectangle border takes one colour and its radius is circular, while the
windows use rounding 15 at rounding_power 4, a superellipse. So the body
and the border are both drawn by a Shape from an SVG path whose corners
are the cubic fit to |x|^4 + |y|^4 = 1, and the border is a ring filled
odd-even, which keeps the translucent body from showing the gradient
through.

One angle drives every balloon, so they turn together, and the
animation runs only while the stack is mapped. Hyprland's borderangle
(speed 30) reads as 3s a turn, which looked slow on a balloon that size,
so the turn is 1.5s, tuned by eye.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 57 insertions, 4 deletions

diff --git a/notifications/NotificationBalloon.qml b/notifications/NotificationBalloon.qml
index b01a848..a9f9459 100644
--- a/notifications/NotificationBalloon.qml
+++ b/notifications/NotificationBalloon.qml
@@ -10,6 +10,7 @@
 // GNU General Public License for more details.
 
 import QtQuick
+import QtQuick.Shapes
 
 // One balloon: icon at the left, app, summary and body, an X, and the click
 // targets. The body is markup, which is why the daemon advertises body-markup.
@@ -22,6 +23,8 @@ Rectangle {
     // silently arrives undefined and every binding on it fails.
     property var notification
     property double now: 0
+    property var borderColors: []
+    property real borderAngle: 0
 
     // Driven by the shell's tick. The balloon drops itself once its expiry
     // passes, or while a suppression says so: the drawer and snooze withhold
@@ -38,10 +41,60 @@ Rectangle {
 
     width: parent ? parent.width : 340
     implicitHeight: texts.implicitHeight + 20 + (preview.visible ? preview.height + 8 : 0)
-    radius: 10
-    color: Qt.alpha(Theme.base, 0.82)
-    border.width: 1
-    border.color: Qt.alpha(Theme.text, 0.12)
+    // The body is drawn by the Shape below, not by the Rectangle, so its
+    // corners can be Hyprland's: rounding 15 at rounding_power 4, a
+    // superellipse a Rectangle radius cannot draw.
+    color: "transparent"
+
+    // A rounded rectangle as an SVG path, each corner the cubic that best
+    // fits |x|^4 + |y|^4 = 1. A circle's control points sit 0.552 of the
+    // radius from each end; matching the superellipse at 45 degrees,
+    // (4 + 3k) / 8 = 2^-1/4, puts them at k = 0.909.
+    function squircle(x, y, w, h, r) {
+        const c = r * (1 - 0.909);
+        const R = x + w, B = y + h;
+        return `M ${x + r} ${y} L ${R - r} ${y} C ${R - c} ${y} ${R} ${y + c} ${R} ${y + r}`
+             + ` L ${R} ${B - r} C ${R} ${B - c} ${R - c} ${B} ${R - r} ${B}`
+             + ` L ${x + r} ${B} C ${x + c} ${B} ${x} ${B - c} ${x} ${B - r}`
+             + ` L ${x} ${y + r} C ${x} ${y + c} ${x + c} ${y} ${x + r} ${y} Z`;
+    }
+
+    // Hyprland's window border: 2px, the udt gradient, rotating. A Rectangle
+    // border takes one colour, so this is a ring, two squircles
+    // filled odd-even, which keeps the translucent body from showing the
+    // gradient through. The gradient line runs through the centre at the
+    // current angle and is just long enough to span the box.
+    // ponytail: three stops, which is what udt-accent writes; GradientStops
+    // cannot come from a Repeater, so a longer list would need more stops.
+    Shape {
+        id: ring
+        anchors.fill: parent
+        preferredRendererType: Shape.CurveRenderer
+        readonly property real dx: Math.cos(b.borderAngle)
+        readonly property real dy: Math.sin(b.borderAngle)
+        readonly property real reach: Math.abs(width / 2 * dx) + Math.abs(height / 2 * dy)
+
+        ShapePath {
+            strokeWidth: -1
+            fillColor: Qt.alpha(Theme.base, 0.82)
+            PathSvg { path: b.squircle(0, 0, ring.width, ring.height, 15) }
+        }
+
+        ShapePath {
+            strokeWidth: -1
+            fillRule: ShapePath.OddEvenFill
+            fillGradient: LinearGradient {
+                x1: ring.width / 2 - ring.dx * ring.reach
+                y1: ring.height / 2 - ring.dy * ring.reach
+                x2: ring.width / 2 + ring.dx * ring.reach
+                y2: ring.height / 2 + ring.dy * ring.reach
+                GradientStop { position: 0.0; color: b.borderColors[0] ?? Theme.accent }
+                GradientStop { position: 0.5; color: b.borderColors[1] ?? Theme.accent }
+                GradientStop { position: 1.0; color: b.borderColors[2] ?? Theme.accent }
+            }
+            PathSvg { path: b.squircle(0, 0, ring.width, ring.height, 15) + " " + b.squircle(2, 2, ring.width - 4, ring.height - 4, 13) }
+        }
+    }
 
     // The background click target is declared first so the X, declared later,
     // sits above it and wins its corner.