Warn in the editor and startup header when using software rendering

Software rendering is very slow and is meant to be used for automated
testing only (on servers without a GPU).

`--no-header` skips the startup warning if specified on the command line.

doc/classes/RenderingServer.xml

@@ -1609,7 +1609,8 @@
 			<return type="int" enum="RenderingDevice.DeviceType" />
 			<description>
 				Returns the type of the video adapter. Since dedicated graphics cards from a given generation will [i]usually[/i] be significantly faster than integrated graphics made in the same generation, the device type can be used as a basis for automatic graphics settings adjustment. However, this is not always true, so make sure to provide users with a way to manually override graphics settings.
-				[b]Note:[/b] When using the OpenGL backend or when running in headless mode, this function always returns [constant RenderingDevice.DEVICE_TYPE_OTHER].
+				[b]Note:[/b] When running the OpenGL driver, this function returns [constant RenderingDevice.DEVICE_TYPE_CPU] for software-emulated GPUs (such as llvmpipe) and [constant RenderingDevice.DEVICE_TYPE_OTHER] for all other device types. The detection is based on the video adapter name, as OpenGL does not have an actual API for querying the current device type.
+				[b]Note:[/b] When running in headless mode, this function always returns [constant RenderingDevice.DEVICE_TYPE_OTHER].
 			</description>
 		</method>
 		<method name="get_video_adapter_vendor" qualifiers="const">

drivers/gles3/rasterizer_gles3.cpp

@@ -194,6 +194,11 @@ typedef void(GLAPIENTRY *DebugMessageCallbackARB)(DEBUGPROCARB callback, const v
 void RasterizerGLES3::initialize() {
 	Engine::get_singleton()->print_header(vformat("OpenGL API %s - Compatibility - Using Device: %s - %s", RS::get_singleton()->get_video_adapter_api_version(), RS::get_singleton()->get_video_adapter_vendor(), RS::get_singleton()->get_video_adapter_name()));
 
+	if (RS::get_singleton()->get_video_adapter_type() == RenderingDevice::DEVICE_TYPE_CPU) {
+		Engine::get_singleton()->print_header_rich(
+				"[color=yellow][b]WARNING:[/b] OpenGL is currently running on software emulation, which is very slow. Check whether your GPU supports OpenGL and make sure its drivers are up-to-date.");
+	}
+
 	// FLIP XY Bug: Are more devices affected?
 	// Confirmed so far: all Adreno 3xx with old driver (until 2018)
 	// ok on some tested Adreno devices: 4xx, 5xx and 6xx

drivers/gles3/storage/utilities.cpp

@@ -454,6 +454,13 @@ String Utilities::get_video_adapter_vendor() const {
 }
 
 RenderingDevice::DeviceType Utilities::get_video_adapter_type() const {
+	// Detect common OpenGL software rasterizers according to the reported GPU model name.
+	// See <https://github.com/pal1000/mesa-dist-win>.
+	const String adapter_name = get_video_adapter_name().to_lower();
+	if (adapter_name.contains("llvmpipe") || adapter_name.contains("softpipe") || adapter_name.contains("swr")) {
+		return RenderingDevice::DeviceType::DEVICE_TYPE_CPU;
+	}
+
 	return RenderingDevice::DeviceType::DEVICE_TYPE_OTHER;
 }
 

editor/editor_node.cpp

@@ -723,6 +723,28 @@ void EditorNode::_notification(int p_what) {
 			CanvasItemEditor::ThemePreviewMode theme_preview_mode = (CanvasItemEditor::ThemePreviewMode)(int)EditorSettings::get_singleton()->get_project_metadata("2d_editor", "theme_preview", CanvasItemEditor::THEME_PREVIEW_PROJECT);
 			update_preview_themes(theme_preview_mode);
 
+			if (RenderingDevice::get_singleton() && RenderingDevice::get_singleton()->get_device_type() == RenderingDevice::DEVICE_TYPE_CPU) {
+				const String driver_name = OS::get_singleton()->get_current_rendering_driver_name();
+				String driver_friendly_name;
+				if (driver_name == "d3d12") {
+					driver_friendly_name = "Direct3D 12";
+				} else if (driver_name == "metal") {
+					driver_friendly_name = "Metal";
+				} else {
+					driver_friendly_name = "Vulkan";
+				}
+				log->add_message(
+						vformat(TTR("%s is currently running on software emulation, which is very slow. Check whether your GPU supports %s and make sure its drivers are up-to-date.\nIf your GPU is not compatible with %s, try switching to the Compatibility rendering method in the top-right corner of the editor."),
+								driver_friendly_name,
+								driver_friendly_name,
+								driver_friendly_name),
+						EditorLog::MSG_TYPE_WARNING);
+			} else if (RenderingServer::get_singleton()->get_video_adapter_type() == RenderingDevice::DEVICE_TYPE_CPU) {
+				log->add_message(
+						TTR("OpenGL is currently running on software emulation, which is very slow. Check whether your GPU supports OpenGL and make sure its drivers are up-to-date.\nIf your GPU is not compatible with OpenGL, try switching to the Forward+ or Mobile rendering methods in the top-right corner of the editor."),
+						EditorLog::MSG_TYPE_WARNING);
+			}
+
 			/* DO NOT LOAD SCENES HERE, WAIT FOR FILE SCANNING AND REIMPORT TO COMPLETE */
 		} break;
 

servers/rendering/rendering_device.cpp

@@ -5382,6 +5382,22 @@ Error RenderingDevice::initialize(RenderingContextDriver *p_context, DisplayServ
 
 		// Output our device version.
 		Engine::get_singleton()->print_header(vformat("%s %s - %s - Using Device #%d: %s - %s", get_device_api_name(), get_device_api_version(), rendering_method, device_index, _get_device_vendor_name(device), device.name));
+
+		if (get_device_type() == DEVICE_TYPE_CPU) {
+			const String driver_name = OS::get_singleton()->get_current_rendering_driver_name();
+			String driver_friendly_name;
+			if (driver_name == "d3d12") {
+				driver_friendly_name = "Direct3D 12";
+			} else if (driver_name == "metal") {
+				driver_friendly_name = "Metal";
+			} else {
+				driver_friendly_name = "Vulkan";
+			}
+			Engine::get_singleton()->print_header_rich(
+					vformat("[color=yellow][b]WARNING:[/b] %s is currently running on software emulation, which is very slow. Check whether your GPU supports %s and make sure its drivers are up-to-date.",
+							driver_friendly_name,
+							driver_friendly_name));
+		}
 	}
 
 	// Pick the main queue family. It is worth noting we explicitly do not request the transfer bit, as apparently the specification defines