[Windows] HDR Output: Emit window events when HDR state changes

doc/classes/DisplayServer.xml

@@ -3375,6 +3375,11 @@
 			Sent when the window has been forcibly closed by the display server. The window will immediately hide and clean any internal rendering references.
 			[b]Note:[/b] This flag is implemented only on Linux (Wayland).
 		</constant>
+		<constant name="WINDOW_EVENT_OUTPUT_MAX_LINEAR_VALUE_CHANGED" value="9" enum="WindowEvent">
+			Sent when the output max linear value returned by [method Window.get_output_max_linear_value] has changed.
+			This occurs when HDR output is enabled or disabled and when any HDR output luminance values of the window have changed, such as when the player adjusts their screen brightness setting or moves the window to a different screen.
+			[b]Note:[/b] This flag is implemented only on Windows.
+		</constant>
 		<constant name="WINDOW_EDGE_TOP_LEFT" value="0" enum="WindowResizeEdge">
 			Top-left edge of a window.
 		</constant>

doc/classes/Node.xml

@@ -1276,6 +1276,10 @@
 		<constant name="NOTIFICATION_WM_POSITION_CHANGED" value="1012">
 			Notification received when the window is moved.
 		</constant>
+		<constant name="NOTIFICATION_WM_OUTPUT_MAX_LINEAR_VALUE_CHANGED" value="1013">
+			Notification received when the output max linear value returned by [method Window.get_output_max_linear_value] has changed.
+			This occurs when HDR output is enabled or disabled and when any HDR output luminance values of the window have changed, such as when the player adjusts their screen brightness setting or moves the window to a different screen.
+		</constant>
 		<constant name="NOTIFICATION_OS_MEMORY_WARNING" value="2009">
 			Notification received from the OS when the application is exceeding its allocated memory.
 			Implemented only on iOS.

doc/classes/Window.xml

@@ -123,8 +123,8 @@
 		<method name="get_output_max_linear_value" qualifiers="const">
 			<return type="float" />
 			<description>
-				Returns the maximum value for linear color components that can be displayed in this window, regardless of SDR or HDR output. Returns [code]1.0[/code] if HDR is not enabled or not supported. This value is used by tonemapping and other [Environment] effects to ensure that bright colors are presented in the range that can be displayed by this window.
-				When using the Linear tonemapper without [Environment] effects or no [WorldEnvironment], use the returned value to scale content to maximize the screen's brightness, such as for lasers or other bright effects. The following is an example that produces the brightest purple color that the screen can produce:
+				Returns the maximum value for linear color components that can be displayed in this window, regardless of SDR or HDR output. Returns [code]1.0[/code] if HDR is not enabled or not supported. The [signal output_max_linear_value_changed] signal will be emitted whenever this value changes.
+				This value is used by tonemapping and other [Environment] effects to ensure that bright colors are presented in the range that can be displayed by this window. When using the Linear tonemapper without [Environment] effects or no [WorldEnvironment], use the returned value to scale content to maximize the screen's brightness, such as for lasers or other bright effects. The following is an example that produces the brightest purple color that the screen can produce:
 				[codeblocks]
 				[gdscript]
 				func _process(_delta):
@@ -867,6 +867,12 @@
 				Emitted when the mouse event is received by the custom decoration area defined by [member nonclient_area], and normal input to the window is blocked (such as when it has an exclusive child opened). [param event]'s position is in the embedder's coordinate system.
 			</description>
 		</signal>
+		<signal name="output_max_linear_value_changed">
+			<param index="0" name="output_max_linear_value" type="float" />
+			<description>
+				Emitted when the output max linear value returned by [method Window.get_output_max_linear_value] has changed. This occurs when HDR output is enabled or disabled and when any HDR output luminance values of the window have changed, such as when the player adjusts their screen brightness setting or moves the window to a different screen. [param output_max_linear_value] is the new value.
+			</description>
+		</signal>
 		<signal name="theme_changed">
 			<description>
 				Emitted when the [constant NOTIFICATION_THEME_CHANGED] notification is sent.

platform/windows/display_server_windows.cpp

@@ -3422,27 +3422,42 @@ void DisplayServerWindows::_update_hdr_output_for_window(DisplayServerEnums::Win
 	if (rendering_context) {
 		bool current_hdr_enabled = rendering_context->window_get_hdr_output_enabled(p_window);
 		bool desired_hdr_enabled = p_window_data.hdr_output_requested && p_screen_data.hdr_supported;
+		bool hdr_state_changed = false;
 
 		if (current_hdr_enabled != desired_hdr_enabled) {
 			rendering_context->window_set_hdr_output_enabled(p_window, desired_hdr_enabled);
 			rendering_context->window_set_hdr_output_linear_luminance_scale(p_window, 80.0f);
+			hdr_state_changed = true;
 		}
 
 		// If auto reference luminance is enabled, update it based on the current SDR white level.
 		if (p_window_data.hdr_output_reference_luminance < 0.0f) {
 			if (p_screen_data.sdr_white_level > 0.0f) {
-				rendering_context->window_set_hdr_output_reference_luminance(p_window, p_screen_data.sdr_white_level);
+				float current_ref_luminance = rendering_context->window_get_hdr_output_reference_luminance(p_window);
+				if (!Math::is_equal_approx(current_ref_luminance, p_screen_data.sdr_white_level)) {
+					rendering_context->window_set_hdr_output_reference_luminance(p_window, p_screen_data.sdr_white_level);
+					hdr_state_changed = true;
+				}
 			}
 			// If we cannot get the SDR white level, leave the previous value unchanged.
 		}
 
 		// If auto max luminance is enabled, update it based on the screen's max luminance.
 		if (p_window_data.hdr_output_max_luminance < 0.0f) {
 			if (p_screen_data.max_luminance > 0.0f) {
-				rendering_context->window_set_hdr_output_max_luminance(p_window, p_screen_data.max_luminance);
+				float current_max_luminance = rendering_context->window_get_hdr_output_max_luminance(p_window);
+				if (!Math::is_equal_approx(current_max_luminance, p_screen_data.max_luminance)) {
+					rendering_context->window_set_hdr_output_max_luminance(p_window, p_screen_data.max_luminance);
+					hdr_state_changed = true;
+				}
 			}
 			// If we cannot get the screen's max luminance, leave the previous value unchanged.
 		}
+
+		// Trigger HDR output changed event if any HDR parameter was modified.
+		if (hdr_state_changed) {
+			_send_window_event(p_window_data, DisplayServerEnums::WINDOW_EVENT_OUTPUT_MAX_LINEAR_VALUE_CHANGED);
+		}
 	}
 #endif // RD_ENABLED
 }
@@ -4684,6 +4699,7 @@ void DisplayServerWindows::window_set_hdr_output_reference_luminance(const float
 #if defined(RD_ENABLED)
 		if (rendering_context) {
 			rendering_context->window_set_hdr_output_reference_luminance(p_window, p_reference_luminance);
+			_send_window_event(wd, DisplayServerEnums::WINDOW_EVENT_OUTPUT_MAX_LINEAR_VALUE_CHANGED);
 		}
 #endif
 	}
@@ -4729,6 +4745,7 @@ void DisplayServerWindows::window_set_hdr_output_max_luminance(const float p_max
 #if defined(RD_ENABLED)
 		if (rendering_context) {
 			rendering_context->window_set_hdr_output_max_luminance(p_window, p_max_luminance);
+			_send_window_event(wd, DisplayServerEnums::WINDOW_EVENT_OUTPUT_MAX_LINEAR_VALUE_CHANGED);
 		}
 #endif
 	}

scene/main/node.cpp

@@ -3966,6 +3966,7 @@ void Node::_bind_methods() {
 	BIND_CONSTANT(NOTIFICATION_VP_MOUSE_ENTER);
 	BIND_CONSTANT(NOTIFICATION_VP_MOUSE_EXIT);
 	BIND_CONSTANT(NOTIFICATION_WM_POSITION_CHANGED);
+	BIND_CONSTANT(NOTIFICATION_WM_OUTPUT_MAX_LINEAR_VALUE_CHANGED);
 	BIND_CONSTANT(NOTIFICATION_OS_MEMORY_WARNING);
 	BIND_CONSTANT(NOTIFICATION_TRANSLATION_CHANGED);
 	BIND_CONSTANT(NOTIFICATION_WM_ABOUT);

scene/main/node.h

@@ -487,6 +487,7 @@ class Node : public Object {
 		NOTIFICATION_VP_MOUSE_ENTER = 1010,
 		NOTIFICATION_VP_MOUSE_EXIT = 1011,
 		NOTIFICATION_WM_POSITION_CHANGED = 1012,
+		NOTIFICATION_WM_OUTPUT_MAX_LINEAR_VALUE_CHANGED = 1013,
 
 		// Keep these in sync with MainLoop.
 		NOTIFICATION_OS_MEMORY_WARNING = 2009,

scene/main/window.cpp

@@ -925,6 +925,10 @@ void Window::_event_callback(DisplayServerEnums::WindowEvent p_event) {
 		case DisplayServerEnums::WINDOW_EVENT_FORCE_CLOSE: {
 			hide();
 		} break;
+		case DisplayServerEnums::WINDOW_EVENT_OUTPUT_MAX_LINEAR_VALUE_CHANGED: {
+			_propagate_window_notification(this, NOTIFICATION_WM_OUTPUT_MAX_LINEAR_VALUE_CHANGED);
+			emit_signal(SNAME("output_max_linear_value_changed"), get_output_max_linear_value());
+		} break;
 	}
 }
 
@@ -3589,6 +3593,7 @@ void Window::_bind_methods() {
 	ADD_SIGNAL(MethodInfo("dpi_changed"));
 	ADD_SIGNAL(MethodInfo("titlebar_changed"));
 	ADD_SIGNAL(MethodInfo("title_changed"));
+	ADD_SIGNAL(MethodInfo("output_max_linear_value_changed", PropertyInfo(Variant::FLOAT, "output_max_linear_value")));
 
 	BIND_CONSTANT(NOTIFICATION_VISIBILITY_CHANGED);
 	BIND_CONSTANT(NOTIFICATION_THEME_CHANGED);

servers/display/display_server.cpp

@@ -1966,6 +1966,7 @@ void DisplayServer::_bind_methods() {
 	BIND_ENUM_CONSTANT(DisplayServerEnums::WINDOW_EVENT_DPI_CHANGE);
 	BIND_ENUM_CONSTANT(DisplayServerEnums::WINDOW_EVENT_TITLEBAR_CHANGE);
 	BIND_ENUM_CONSTANT(DisplayServerEnums::WINDOW_EVENT_FORCE_CLOSE);
+	BIND_ENUM_CONSTANT(DisplayServerEnums::WINDOW_EVENT_OUTPUT_MAX_LINEAR_VALUE_CHANGED);
 
 	BIND_ENUM_CONSTANT(DisplayServerEnums::WINDOW_EDGE_TOP_LEFT);
 	BIND_ENUM_CONSTANT(DisplayServerEnums::WINDOW_EDGE_TOP);

servers/display/display_server_enums.h

@@ -245,6 +245,7 @@ enum WindowEvent {
 	WINDOW_EVENT_DPI_CHANGE,
 	WINDOW_EVENT_TITLEBAR_CHANGE,
 	WINDOW_EVENT_FORCE_CLOSE,
+	WINDOW_EVENT_OUTPUT_MAX_LINEAR_VALUE_CHANGED,
 };
 
 enum WindowResizeEdge {