Fallback to OpenGL 3 if other rendering drivers are not supported

doc/classes/ProjectSettings.xml

@@ -2795,6 +2795,10 @@
 			If [code]true[/code], the forward renderer will fall back to Direct3D 12 if Vulkan is not supported.
 			[b]Note:[/b] This setting is implemented only on Windows.
 		</member>
+		<member name="rendering/rendering_device/fallback_to_opengl3" type="bool" setter="" getter="" default="true">
+			If [code]true[/code], the forward renderer will fall back to OpenGL 3 if both Direct3D 12, Metal and Vulkan are not supported.
+			[b]Note:[/b] This setting is implemented only on Windows, Android, macOS, iOS, and Linux/X11.
+		</member>
 		<member name="rendering/rendering_device/fallback_to_vulkan" type="bool" setter="" getter="" default="true">
 			If [code]true[/code], the forward renderer will fall back to Vulkan if Direct3D 12 is not supported.
 			[b]Note:[/b] This setting is implemented only on Windows.

main/main.cpp

@@ -1977,6 +1977,7 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 
 		GLOBAL_DEF_RST("rendering/rendering_device/fallback_to_vulkan", true);
 		GLOBAL_DEF_RST("rendering/rendering_device/fallback_to_d3d12", true);
+		GLOBAL_DEF_RST("rendering/rendering_device/fallback_to_opengl3", true);
 	}
 
 	{

platform/android/display_server_android.cpp

@@ -607,11 +607,19 @@ DisplayServerAndroid::DisplayServerAndroid(const String &p_rendering_driver, Dis
 
 	if (rendering_context) {
 		if (rendering_context->initialize() != OK) {
-			ERR_PRINT(vformat("Failed to initialize %s context", rendering_driver));
 			memdelete(rendering_context);
 			rendering_context = nullptr;
-			r_error = ERR_UNAVAILABLE;
-			return;
+			bool fallback_to_opengl3 = GLOBAL_GET("rendering/rendering_device/fallback_to_opengl3");
+			if (fallback_to_opengl3 && rendering_driver != "opengl3") {
+				WARN_PRINT("Your device seem not to support Vulkan, switching to OpenGL 3.");
+				rendering_driver = "opengl3";
+				OS::get_singleton()->set_current_rendering_method("gl_compatibility");
+				OS::get_singleton()->set_current_rendering_driver_name(rendering_driver);
+			} else {
+				ERR_PRINT(vformat("Failed to initialize %s context", rendering_driver));
+				r_error = ERR_UNAVAILABLE;
+				return;
+			}
 		}
 
 		union {

platform/ios/display_server_ios.mm

@@ -107,11 +107,19 @@
 #endif
 	if (rendering_context) {
 		if (rendering_context->initialize() != OK) {
-			ERR_PRINT(vformat("Failed to initialize %s context", rendering_driver));
 			memdelete(rendering_context);
 			rendering_context = nullptr;
-			r_error = ERR_UNAVAILABLE;
-			return;
+			bool fallback_to_opengl3 = GLOBAL_GET("rendering/rendering_device/fallback_to_opengl3");
+			if (fallback_to_opengl3 && rendering_driver != "opengl3") {
+				WARN_PRINT("Your device seem not to support MoltenVK or Metal, switching to OpenGL 3.");
+				rendering_driver = "opengl3";
+				OS::get_singleton()->set_current_rendering_method("gl_compatibility");
+				OS::get_singleton()->set_current_rendering_driver_name(rendering_driver);
+			} else {
+				ERR_PRINT(vformat("Failed to initialize %s context", rendering_driver));
+				r_error = ERR_UNAVAILABLE;
+				return;
+			}
 		}
 
 		if (rendering_context->window_create(MAIN_WINDOW_ID, &wpd) != OK) {

platform/linuxbsd/x11/display_server_x11.cpp

@@ -6160,20 +6160,28 @@ DisplayServerX11::DisplayServerX11(const String &p_rendering_driver, WindowMode
 		if (rendering_context->initialize() != OK) {
 			memdelete(rendering_context);
 			rendering_context = nullptr;
-			r_error = ERR_CANT_CREATE;
+			bool fallback_to_opengl3 = GLOBAL_GET("rendering/rendering_device/fallback_to_opengl3");
+			if (fallback_to_opengl3 && rendering_driver != "opengl3") {
+				WARN_PRINT("Your video card drivers seem not to support the required Vulkan version, switching to OpenGL 3.");
+				rendering_driver = "opengl3";
+				OS::get_singleton()->set_current_rendering_method("gl_compatibility");
+				OS::get_singleton()->set_current_rendering_driver_name(rendering_driver);
+			} else {
+				r_error = ERR_CANT_CREATE;
+
+				if (p_rendering_driver == "vulkan") {
+					OS::get_singleton()->alert(
+							vformat("Your video card drivers seem not to support the required Vulkan version.\n\n"
+									"If possible, consider updating your video card drivers or using the OpenGL 3 driver.\n\n"
+									"You can enable the OpenGL 3 driver by starting the engine from the\n"
+									"command line with the command:\n\n    \"%s\" --rendering-driver opengl3\n\n"
+									"If you recently updated your video card drivers, try rebooting.",
+									executable_name),
+							"Unable to initialize Vulkan video driver");
+				}
 
-			if (p_rendering_driver == "vulkan") {
-				OS::get_singleton()->alert(
-						vformat("Your video card drivers seem not to support the required Vulkan version.\n\n"
-								"If possible, consider updating your video card drivers or using the OpenGL 3 driver.\n\n"
-								"You can enable the OpenGL 3 driver by starting the engine from the\n"
-								"command line with the command:\n\n    \"%s\" --rendering-driver opengl3\n\n"
-								"If you recently updated your video card drivers, try rebooting.",
-								executable_name),
-						"Unable to initialize Vulkan video driver");
+				ERR_FAIL_MSG(vformat("Could not initialize %s", rendering_driver));
 			}
-
-			ERR_FAIL_MSG(vformat("Could not initialize %s", rendering_driver));
 		}
 		driver_found = true;
 	}

platform/macos/display_server_macos.mm

@@ -3649,8 +3649,16 @@
 		if (rendering_context->initialize() != OK) {
 			memdelete(rendering_context);
 			rendering_context = nullptr;
-			r_error = ERR_CANT_CREATE;
-			ERR_FAIL_MSG("Could not initialize " + rendering_driver);
+			bool fallback_to_opengl3 = GLOBAL_GET("rendering/rendering_device/fallback_to_opengl3");
+			if (fallback_to_opengl3 && rendering_driver != "opengl3") {
+				WARN_PRINT("Your device seem not to support MoltenVK or Metal, switching to OpenGL 3.");
+				rendering_driver = "opengl3";
+				OS::get_singleton()->set_current_rendering_method("gl_compatibility");
+				OS::get_singleton()->set_current_rendering_driver_name(rendering_driver);
+			} else {
+				r_error = ERR_CANT_CREATE;
+				ERR_FAIL_MSG("Could not initialize " + rendering_driver);
+			}
 		}
 	}
 #endif

platform/windows/display_server_windows.cpp

@@ -6177,6 +6177,17 @@ DisplayServerWindows::DisplayServerWindows(const String &p_rendering_driver, Win
 				}
 			}
 #endif
+			bool fallback_to_opengl3 = GLOBAL_GET("rendering/rendering_device/fallback_to_opengl3");
+			if (failed && fallback_to_opengl3 && rendering_driver != "opengl3") {
+				memdelete(rendering_context);
+				rendering_context = nullptr;
+				tested_drivers.set_flag(DRIVER_ID_COMPAT_OPENGL3);
+				WARN_PRINT("Your video card drivers seem not to support Direct3D 12 or Vulkan, switching to OpenGL 3.");
+				rendering_driver = "opengl3";
+				OS::get_singleton()->set_current_rendering_method("gl_compatibility");
+				OS::get_singleton()->set_current_rendering_driver_name(rendering_driver);
+				failed = false;
+			}
 			if (failed) {
 				memdelete(rendering_context);
 				rendering_context = nullptr;