ClientUI: Add support for changing window opacity.

runelite-client/src/main/java/net/runelite/client/config/RuneLiteConfig.java

@@ -105,11 +105,26 @@ public interface RuneLiteConfig extends Config
 		return true;
 	}
 
+	@Range(
+		min = 10,
+		max = 100
+	)
+	@ConfigItem(
+		keyName = "uiWindowOpacity",
+		name = "Window opacity",
+		description = "Set the windows opacity. Requires \"Enable custom window chrome\" to be enabled.",
+		position = 16
+	)
+	default int windowOpacity()
+	{
+		return 100;
+	}
+
 	@ConfigItem(
 		keyName = "gameAlwaysOnTop",
 		name = "Enable client always on top",
 		description = "The game will always be on the top of the screen",
-		position = 16
+		position = 17
 	)
 	default boolean gameAlwaysOnTop()
 	{
@@ -120,7 +135,7 @@ public interface RuneLiteConfig extends Config
 		keyName = "warningOnExit",
 		name = "Display warning on exit",
 		description = "Toggles a warning popup when trying to exit the client",
-		position = 17
+		position = 18
 	)
 	default WarningOnExit warningOnExit()
 	{
@@ -131,7 +146,7 @@ public interface RuneLiteConfig extends Config
 		keyName = "usernameInTitle",
 		name = "Show display name in title",
 		description = "Toggles displaying of local player's display name in client title",
-		position = 18
+		position = 19
 	)
 	default boolean usernameInTitle()
 	{

runelite-client/src/main/java/net/runelite/client/ui/ClientUI.java

@@ -161,7 +161,7 @@ public class ClientUI
 	@Subscribe
 	public void onConfigChanged(ConfigChanged event)
 	{
-		if (!event.getGroup().equals("runelite") ||
+		if (!event.getGroup().equals(CONFIG_GROUP) ||
 			event.getKey().equals(CONFIG_CLIENT_MAXIMIZED) ||
 			event.getKey().equals(CONFIG_CLIENT_BOUNDS))
 		{
@@ -979,6 +979,14 @@ public class ClientUI
 			return;
 		}
 
+		// Update window opacity if the frame is undecorated, translucency capable and not fullscreen
+		if (frame.isUndecorated() &&
+			frame.getGraphicsConfiguration().isTranslucencyCapable() &&
+			frame.getGraphicsConfiguration().getDevice().getFullScreenWindow() == null)
+		{
+			frame.setOpacity(((float) config.windowOpacity()) / 100.0f);
+		}
+
 		if (config.usernameInTitle() && (client instanceof Client))
 		{
 			final Player player = ((Client)client).getLocalPlayer();