[DisplayServer] Add method to check if window transparency is supported and enabled.

doc/classes/DisplayServer.xml

@@ -930,6 +930,12 @@
 				Returns [code]true[/code] if touch events are available (Android or iOS), the capability is detected on the Web platform or if [member ProjectSettings.input_devices/pointing/emulate_touch_from_mouse] is [code]true[/code].
 			</description>
 		</method>
+		<method name="is_window_transparency_available" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns [code]true[/code] if the window background can be made transparent. This method returns [code]false[/code] if [member ProjectSettings.display/window/per_pixel_transparency/allowed] is set to [code]false[/code], or if transparency is not supported by the renderer or OS compositor.
+			</description>
+		</method>
 		<method name="keyboard_get_current_layout" qualifiers="const">
 			<return type="int" />
 			<description>
@@ -2045,7 +2051,7 @@
 		</constant>
 		<constant name="WINDOW_FLAG_TRANSPARENT" value="3" enum="WindowFlags">
 			The window background can be transparent.
-			[b]Note:[/b] This flag has no effect if [member ProjectSettings.display/window/per_pixel_transparency/allowed] is set to [code]false[/code].
+			[b]Note:[/b] This flag has no effect if [method is_window_transparency_available] returns [code]false[/code].
 			[b]Note:[/b] Transparency support is implemented on Linux (X11/Wayland), macOS, and Windows, but availability might vary depending on GPU driver, display manager, and compositor capabilities.
 		</constant>
 		<constant name="WINDOW_FLAG_NO_FOCUS" value="4" enum="WindowFlags">

drivers/d3d12/rendering_device_driver_d3d12.cpp

@@ -2199,9 +2199,21 @@ Error RenderingDeviceDriverD3D12::swap_chain_resize(CommandQueueID p_cmd_queue,
 		swap_chain_desc.SampleDesc.Count = 1;
 		swap_chain_desc.Flags = creation_flags;
 		swap_chain_desc.Scaling = DXGI_SCALING_NONE;
+		if (OS::get_singleton()->is_layered_allowed()) {
+			swap_chain_desc.AlphaMode = DXGI_ALPHA_MODE_PREMULTIPLIED;
+			has_comp_alpha[(uint64_t)p_cmd_queue.id] = true;
+		} else {
+			swap_chain_desc.AlphaMode = DXGI_ALPHA_MODE_IGNORE;
+			has_comp_alpha[(uint64_t)p_cmd_queue.id] = false;
+		}
 
 		ComPtr<IDXGISwapChain1> swap_chain_1;
 		res = context_driver->dxgi_factory_get()->CreateSwapChainForHwnd(command_queue->d3d_queue.Get(), surface->hwnd, &swap_chain_desc, nullptr, nullptr, swap_chain_1.GetAddressOf());
+		if (!SUCCEEDED(res) && swap_chain_desc.AlphaMode != DXGI_ALPHA_MODE_IGNORE) {
+			swap_chain_desc.AlphaMode = DXGI_ALPHA_MODE_IGNORE;
+			has_comp_alpha[(uint64_t)p_cmd_queue.id] = false;
+			res = context_driver->dxgi_factory_get()->CreateSwapChainForHwnd(command_queue->d3d_queue.Get(), surface->hwnd, &swap_chain_desc, nullptr, nullptr, swap_chain_1.GetAddressOf());
+		}
 		ERR_FAIL_COND_V(!SUCCEEDED(res), ERR_CANT_CREATE);
 
 		swap_chain_1.As(&swap_chain->d3d_swap_chain);
@@ -5980,6 +5992,13 @@ const RDD::Capabilities &RenderingDeviceDriverD3D12::get_capabilities() const {
 	return device_capabilities;
 }
 
+bool RenderingDeviceDriverD3D12::is_composite_alpha_supported(CommandQueueID p_queue) const {
+	if (has_comp_alpha.has((uint64_t)p_queue.id)) {
+		return has_comp_alpha[(uint64_t)p_queue.id];
+	}
+	return false;
+}
+
 /******************/
 
 RenderingDeviceDriverD3D12::RenderingDeviceDriverD3D12(RenderingContextDriverD3D12 *p_context_driver) {

drivers/d3d12/rendering_device_driver_d3d12.h

@@ -973,6 +973,7 @@ private:
 	uint32_t frames_drawn = 0;
 	uint32_t segment_serial = 0;
 	bool segment_begun = false;
+	HashMap<uint64_t, bool> has_comp_alpha;
 
 public:
 	virtual void begin_segment(uint32_t p_frame_index, uint32_t p_frames_drawn) override final;
@@ -994,6 +995,8 @@ public:
 	virtual String get_pipeline_cache_uuid() const override final;
 	virtual const Capabilities &get_capabilities() const override final;
 
+	virtual bool is_composite_alpha_supported(CommandQueueID p_queue) const override final;
+
 	static bool is_in_developer_mode();
 
 private:

drivers/vulkan/rendering_device_driver_vulkan.cpp

@@ -2646,6 +2646,7 @@ Error RenderingDeviceDriverVulkan::swap_chain_resize(CommandQueueID p_cmd_queue,
 				break;
 			}
 		}
+		has_comp_alpha[(uint64_t)p_cmd_queue.id] = (composite_alpha != VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR);
 	}
 
 	VkSwapchainCreateInfoKHR swap_create_info = {};
@@ -4945,6 +4946,13 @@ const RDD::Capabilities &RenderingDeviceDriverVulkan::get_capabilities() const {
 	return device_capabilities;
 }
 
+bool RenderingDeviceDriverVulkan::is_composite_alpha_supported(CommandQueueID p_queue) const {
+	if (has_comp_alpha.has((uint64_t)p_queue.id)) {
+		return has_comp_alpha[(uint64_t)p_queue.id];
+	}
+	return false;
+}
+
 /******************/
 
 RenderingDeviceDriverVulkan::RenderingDeviceDriverVulkan(RenderingContextDriverVulkan *p_context_driver) {

drivers/vulkan/rendering_device_driver_vulkan.h

@@ -494,6 +494,7 @@ private:
 	static int caching_instance_count;
 	PipelineCache pipelines_cache;
 	String pipeline_cache_id;
+	HashMap<uint64_t, bool> has_comp_alpha;
 
 public:
 	virtual void pipeline_free(PipelineID p_pipeline) override final;
@@ -627,6 +628,8 @@ public:
 	virtual String get_pipeline_cache_uuid() const override final;
 	virtual const Capabilities &get_capabilities() const override final;
 
+	virtual bool is_composite_alpha_supported(CommandQueueID p_queue) const override final;
+
 private:
 	/*********************/
 	/**** BOOKKEEPING ****/

platform/linuxbsd/x11/display_server_x11.cpp

@@ -5192,6 +5192,22 @@ void DisplayServerX11::set_context(Context p_context) {
 	}
 }
 
+bool DisplayServerX11::is_window_transparency_available() const {
+	CharString net_wm_cm_name = vformat("_NET_WM_CM_S%d", XDefaultScreen(x11_display)).ascii();
+	Atom net_wm_cm = XInternAtom(x11_display, net_wm_cm_name.get_data(), False);
+	if (net_wm_cm == None) {
+		return false;
+	}
+	if (XGetSelectionOwner(x11_display, net_wm_cm) == None) {
+		return false;
+	}
+
+	if (rendering_device && !rendering_device->is_composite_alpha_supported()) {
+		return false;
+	}
+	return OS::get_singleton()->is_layered_allowed();
+}
+
 void DisplayServerX11::set_native_icon(const String &p_filename) {
 	WARN_PRINT("Native icon not supported by this display server.");
 }

platform/linuxbsd/x11/display_server_x11.h

@@ -530,6 +530,8 @@ public:
 
 	virtual void set_context(Context p_context) override;
 
+	virtual bool is_window_transparency_available() const override;
+
 	virtual void set_native_icon(const String &p_filename) override;
 	virtual void set_icon(const Ref<Image> &p_icon) override;
 

platform/macos/display_server_macos.h

@@ -439,6 +439,8 @@ public:
 	virtual Rect2 status_indicator_get_rect(IndicatorID p_id) const override;
 	virtual void delete_status_indicator(IndicatorID p_id) override;
 
+	virtual bool is_window_transparency_available() const override;
+
 	static DisplayServer *create_func(const String &p_rendering_driver, WindowMode p_mode, VSyncMode p_vsync_mode, uint32_t p_flags, const Vector2i *p_position, const Vector2i &p_resolution, int p_screen, Context p_context, Error &r_error);
 	static Vector<String> get_rendering_drivers_func();
 

platform/macos/display_server_macos.mm

@@ -3314,6 +3314,13 @@ void DisplayServerMacOS::delete_status_indicator(IndicatorID p_id) {
 	indicators.erase(p_id);
 }
 
+bool DisplayServerMacOS::is_window_transparency_available() const {
+	if (rendering_device && !rendering_device->is_composite_alpha_supported()) {
+		return false;
+	}
+	return OS::get_singleton()->is_layered_allowed();
+}
+
 DisplayServer *DisplayServerMacOS::create_func(const String &p_rendering_driver, WindowMode p_mode, VSyncMode p_vsync_mode, uint32_t p_flags, const Vector2i *p_position, const Vector2i &p_resolution, int p_screen, Context p_context, Error &r_error) {
 	DisplayServer *ds = memnew(DisplayServerMacOS(p_rendering_driver, p_mode, p_vsync_mode, p_flags, p_position, p_resolution, p_screen, p_context, r_error));
 	if (r_error != OK) {

platform/windows/display_server_windows.cpp

@@ -3401,6 +3401,19 @@ DisplayServer::VSyncMode DisplayServerWindows::window_get_vsync_mode(WindowID p_
 void DisplayServerWindows::set_context(Context p_context) {
 }
 
+bool DisplayServerWindows::is_window_transparency_available() const {
+	BOOL dwm_enabled = true;
+	if (DwmIsCompositionEnabled(&dwm_enabled) == S_OK) { // Note: Always enabled on Windows 8+, this check can be removed after Windows 7 support is dropped.
+		if (!dwm_enabled) {
+			return false;
+		}
+	}
+	if (rendering_device && !rendering_device->is_composite_alpha_supported()) {
+		return false;
+	}
+	return OS::get_singleton()->is_layered_allowed();
+}
+
 #define MI_WP_SIGNATURE 0xFF515700
 #define SIGNATURE_MASK 0xFFFFFF00
 // Keeping the name suggested by Microsoft, but this macro really answers:

platform/windows/display_server_windows.h

@@ -697,6 +697,8 @@ public:
 
 	virtual void set_context(Context p_context) override;
 
+	virtual bool is_window_transparency_available() const override;
+
 	static DisplayServer *create_func(const String &p_rendering_driver, WindowMode p_mode, VSyncMode p_vsync_mode, uint32_t p_flags, const Vector2i *p_position, const Vector2i &p_resolution, int p_screen, Context p_context, Error &r_error);
 	static Vector<String> get_rendering_drivers_func();
 	static void register_windows_driver();

servers/display_server.cpp

@@ -996,6 +996,8 @@ void DisplayServer::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("tablet_get_current_driver"), &DisplayServer::tablet_get_current_driver);
 	ClassDB::bind_method(D_METHOD("tablet_set_current_driver", "name"), &DisplayServer::tablet_set_current_driver);
 
+	ClassDB::bind_method(D_METHOD("is_window_transparency_available"), &DisplayServer::is_window_transparency_available);
+
 #ifndef DISABLE_DEPRECATED
 	BIND_ENUM_CONSTANT(FEATURE_GLOBAL_MENU);
 #endif

servers/display_server.h

@@ -580,6 +580,8 @@ public:
 
 	virtual void set_context(Context p_context);
 
+	virtual bool is_window_transparency_available() const { return false; }
+
 	static void register_create_function(const char *p_name, CreateFunction p_function, GetRenderingDriversFunction p_get_drivers);
 	static int get_create_function_count();
 	static const char *get_create_function_name(int p_index);

servers/rendering/rendering_device.cpp

@@ -4734,6 +4734,10 @@ String RenderingDevice::get_device_api_name() const {
 	return driver->get_api_name();
 }
 
+bool RenderingDevice::is_composite_alpha_supported() const {
+	return driver->is_composite_alpha_supported(main_queue);
+}
+
 String RenderingDevice::get_device_api_version() const {
 	return driver->get_api_version();
 }

servers/rendering/rendering_device.h

@@ -1360,6 +1360,8 @@ public:
 	String get_device_api_version() const;
 	String get_device_pipeline_cache_uuid() const;
 
+	bool is_composite_alpha_supported() const;
+
 	uint64_t get_driver_resource(DriverResource p_resource, RID p_rid = RID(), uint64_t p_index = 0);
 
 	static RenderingDevice *get_singleton();

servers/rendering/rendering_device_driver.h

@@ -769,6 +769,8 @@ public:
 	virtual String get_pipeline_cache_uuid() const = 0;
 	virtual const Capabilities &get_capabilities() const = 0;
 
+	virtual bool is_composite_alpha_supported(CommandQueueID p_queue) const { return false; }
+
 	/******************/
 
 	virtual ~RenderingDeviceDriver();