Ton down the intensity of the background on dark theme

Similar to What's App, Telegram and Kaidan.

src/qml/RoomPage.qml

@@ -163,6 +163,23 @@ Kirigami.Page {
         Kirigami.Theme.colorSet: Kirigami.Theme.View
         Kirigami.Theme.inherit: false
         color: NeoChatConfig.compactLayout ? Kirigami.Theme.backgroundColor : "transparent"
+
+        Image {
+            visible: !NeoChatConfig.compactLayout && !NeoChatConfig.blur
+            source: "qrc:/qt/qml/org/kde/neochat/timeline/images/chat-page-background.svg"
+            anchors.fill: parent
+            fillMode: Image.Tile
+            horizontalAlignment: Image.AlignLeft
+            verticalAlignment: Image.AlignTop
+
+            function isDarkColor(background: color): bool {
+                const temp = Qt.darker(background, 1);
+                const darkness = 1 - (0.299 * temp.r + 0.587 * temp.g + 0.114 * temp.b);
+                return temp.a > 0 && darkness >= 0.4;
+            }
+
+            opacity: isDarkColor(Kirigami.Theme.backgroundColor) ? 0.2 : 1
+        }
     }
 
     footer: Loader {

src/timeline/CMakeLists.txt

@@ -79,6 +79,7 @@ ecm_add_qml_module(timeline GENERATE_PLUGIN_SOURCE
         images/transfer.svg
         images/wait.svg
         images/walk.svg
+        images/chat-page-background.svg
     DEPENDENCIES
         QtQuick
 )

src/timeline/images/chat-page-background.svg.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: 2022 Raghavendra Kamath <raghu@raghukamath.com>
+
+SPDX-License-Identifier: CC-BY-SA-4.0