fix: pin the login card per SDDM screen window

4 files changed, 71 insertions, 64 deletions

diff --git a/README.md b/README.md
index 3c3df94..e043918 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,10 @@ its colours from the UDT palette, including the wallpaper-snapped accent.
 SDDM merges into the theme config at every greeter start. Wallpaper and accent
 need no root re-run; only theme code changes do.
 
+Set `uiScreen` in the root-owned `theme/theme.conf` to pin the login card to a
+named screen; leave it empty for the primary screen. It does not belong in the
+generated `theme.conf.user`, which is overwritten on every wallpaper change.
+
 ## Install
 
 The theme code is copied by root. UDT's `install.sh` prints the block; run it in
diff --git a/theme/Main.qml b/theme/Main.qml
index e5c529f..a813d6c 100644
--- a/theme/Main.qml
+++ b/theme/Main.qml
@@ -1,9 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0-only
 // Copyright (C) 2026 Danilo M. <danix@danix.xyz>
 //
-// UDT SDDM greeter. The root item spans every screen. The wallpaper is drawn
-// once per screen; the login card is pinned to one screen (config uiScreen,
-// else the primary screen); input wakes the card after it fades.
+// UDT SDDM greeter. SDDM creates one window per screen, each sized to its own
+// screen and carrying a one-row ScreenModel, so this root item is exactly one
+// screen. The wallpaper fills it; the login card draws only on the screen
+// named by config uiScreen, else on the primary screen. Input wakes the card
+// after it fades.
 
 import QtQuick
 import "components"
@@ -11,81 +13,68 @@ import "components"
 Item {
     id: root
 
-    // SDDM sizes the greeter to the union of every screen.
-    readonly property var union: screenModel.geometry(-1)
-    width: union.width
-    height: union.height
+    // SDDM creates one window per screen and sizes it to that screen. The
+    // model holds exactly one row and geometry(index) ignores index, returning
+    // this window's own screen at origin (0,0).
+    readonly property var windowGeometry: screenModel.geometry(0)
+    width: windowGeometry.width
+    height: windowGeometry.height
 
     // Palette. Values come from theme.conf, overridden live by theme.conf.user.
     readonly property string baseColor: config.stringValue("base")
-    readonly property int cardRadius: 10
     readonly property string wallpaperUrl:
         config.stringValue("background") === ""
             ? ""
             : "file://" + config.stringValue("background")
 
+    // The screen the card belongs on: config uiScreen if non-empty, else the
+    // primary screen. `primaryScreen` is a per-window context property SDDM
+    // sets true only on the window showing the primary screen.
     readonly property string wantedScreen: config.stringValue("uiScreen")
-    property var primaryGeometry: screenModel.geometry(screenModel.primary >= 0 ? screenModel.primary : 0)
-    property var namedGeometry: primaryGeometry
-    readonly property var cardGeometry: wantedScreen === "" ? primaryGeometry : namedGeometry
+    property string thisScreenName: ""
+    readonly property bool cardScreen: wantedScreen === ""
+        ? primaryScreen
+        : (thisScreenName === wantedScreen)
+
+    // The wallpaper fills this window's single screen. The frosted card
+    // samples this image.
+    Image {
+        id: wallpaperImage
+        anchors.fill: parent
+        source: root.wallpaperUrl
+        fillMode: Image.PreserveAspectCrop
+        sourceSize.width: width
+        sourceSize.height: height
+        smooth: true
+        asynchronous: true
+    }
 
-    // The Image delegate of the screen the card sits on. The frosted card
-    // samples it. Null until the model has populated.
-    property Item cardScreenImage: null
+    // Scrim so the card and text read on any wallpaper.
+    Rectangle {
+        anchors.fill: parent
+        color: root.baseColor
+        opacity: 0.45
+    }
 
+    // Non-visual: reads the model's single row to learn this screen's name.
     Repeater {
-        id: screens
         model: screenModel
         delegate: Item {
-            x: geometry.x
-            y: geometry.y
-            width: geometry.width
-            height: geometry.height
-
-            Image {
-                id: screenImage
-                anchors.fill: parent
-                source: root.wallpaperUrl
-                fillMode: Image.PreserveAspectCrop
-                sourceSize.width: parent.width
-                sourceSize.height: parent.height
-                smooth: true
-                asynchronous: true
-            }
-
-            // Scrim so the card and text read on any wallpaper.
-            Rectangle {
-                anchors.fill: parent
-                color: root.baseColor
-                opacity: 0.45
-            }
-
-            readonly property string screenName: name
-
-            Component.onCompleted: root.registerScreen(index, screenName, screenImage, geometry)
+            visible: false
+            Component.onCompleted: root.thisScreenName = name
         }
     }
 
-    // Filled as the model populates: the primary screen's name, and the
-    // wallpaper image plus geometry of whichever screen owns the card.
-    property string primaryName: ""
-
-    function registerScreen(index, screenName, image, geom) {
-        if (index === screenModel.primary)
-            root.primaryName = screenName
-        if (screenName === root.cardScreenName()) {
-            root.cardScreenImage = image
-            root.namedGeometry = geom
-        }
-    }
-
-    function cardScreenName() {
-        return root.wantedScreen !== "" ? root.wantedScreen : root.primaryName
-    }
-
     // Idle: fade the card after fadeoutMs, restore on any input.
     property bool uiVisible: true
 
+    // While faded the card is disabled, which clears its focus; take focus on
+    // the root so the first key press wakes the card instead of vanishing.
+    onUiVisibleChanged: {
+        if (!uiVisible)
+            root.forceActiveFocus()
+    }
+
     Timer {
         id: idle
         interval: config.intValue("fadeoutMs") > 0 ? config.intValue("fadeoutMs") : 60000
@@ -95,7 +84,10 @@ Item {
     }
 
     function wake() {
-        root.uiVisible = true
+        if (!root.uiVisible) {
+            root.uiVisible = true
+            card.restoreFocus()
+        }
         idle.restart()
     }
 
@@ -113,12 +105,12 @@ Item {
 
     LoginCard {
         id: card
-        x: root.cardGeometry.x + (root.cardGeometry.width - width) / 2 + card.shakeOffset
-        y: root.cardGeometry.y + (root.cardGeometry.height - height) / 2
-        backdropSource: root.cardScreenImage
-        visible: opacity > 0
+        anchors.centerIn: parent
+        visible: root.cardScreen
+        enabled: root.uiVisible
         opacity: root.uiVisible ? 1 : 0
         Behavior on opacity { NumberAnimation { duration: 260; easing.type: Easing.OutCubic } }
+        backdropSource: wallpaperImage
         onWake: root.wake()
     }
 }
diff --git a/theme/components/LoginCard.qml b/theme/components/LoginCard.qml
index 5f336d0..d76269f 100644
--- a/theme/components/LoginCard.qml
+++ b/theme/components/LoginCard.qml
@@ -239,6 +239,15 @@ Item {
         sddm.login(usernameField.text, passwordField.text, sessionBox.currentIndex)
     }
 
+    // Return keyboard focus after the idle fade disabled the card: password
+    // when a username is already filled, else the username field.
+    function restoreFocus() {
+        if (usernameField.text.length > 0)
+            passwordField.forceActiveFocus()
+        else
+            usernameField.forceActiveFocus()
+    }
+
     // Login failure wins the notice line; otherwise Caps Lock, if on.
     property string loginError: ""
     readonly property string message: {
diff --git a/theme/theme.conf b/theme/theme.conf
index c2b8269..b5af812 100644
--- a/theme/theme.conf
+++ b/theme/theme.conf
@@ -26,7 +26,9 @@ blue=#8aadf4
 lavender=#b7bdf8
 accent=#b7bdf8
 
-# Empty uiScreen pins the card to the primary screen.
+# Empty uiScreen pins the card to the primary screen. Set a screen name here,
+# in this root-owned file: theme.conf.user is regenerated on every wallpaper
+# change and is not the place for uiScreen.
 uiScreen=
 # 60000 matches the stock theme's idle timeout.
 fadeoutMs=60000