doctool: Fix differences between headless and Vulkan rendering backends

Fixes #53913.

drivers/vulkan/rendering_device_vulkan.cpp

@@ -8913,6 +8913,8 @@ void RenderingDeviceVulkan::initialize(VulkanContext *p_context, bool p_local_de
 		}
 	}
 
+	// Note: If adding new project settings here, also duplicate their definition in
+	// rendering_server.cpp for headless doctool.
 	staging_buffer_block_size = GLOBAL_DEF("rendering/vulkan/staging_buffer/block_size_kb", 256);
 	staging_buffer_block_size = MAX(4, staging_buffer_block_size);
 	staging_buffer_block_size *= 1024; //kb -> bytes

main/main.cpp

@@ -1343,8 +1343,9 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 		display_driver_idx = 0;
 	}
 
-	if (audio_driver == "") { // specified in project.godot
-		audio_driver = GLOBAL_DEF_RST_NOVAL("audio/driver/driver", AudioDriverManager::get_driver(0)->get_name());
+	GLOBAL_DEF_RST_NOVAL("audio/driver/driver", AudioDriverManager::get_driver(0)->get_name());
+	if (audio_driver == "") { // Specified in project.godot.
+		audio_driver = GLOBAL_GET("audio/driver/driver");
 	}
 
 	for (int i = 0; i < AudioDriverManager::get_driver_count(); i++) {

scene/2d/gpu_particles_2d.cpp

@@ -532,6 +532,7 @@ void GPUParticles2D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_trail_section_subdivisions"), &GPUParticles2D::get_trail_section_subdivisions);
 
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "emitting"), "set_emitting", "is_emitting");
+	ADD_PROPERTY_DEFAULT("emitting", true); // Workaround for doctool in headless mode, as dummy rasterizer always returns false.
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "amount", PROPERTY_HINT_RANGE, "1,1000000,1,exp"), "set_amount", "get_amount");
 	ADD_GROUP("Time", "");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "lifetime", PROPERTY_HINT_RANGE, "0.01,600.0,0.01,or_greater"), "set_lifetime", "get_lifetime");

scene/3d/gpu_particles_3d.cpp

@@ -562,6 +562,7 @@ void GPUParticles3D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_transform_align"), &GPUParticles3D::get_transform_align);
 
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "emitting"), "set_emitting", "is_emitting");
+	ADD_PROPERTY_DEFAULT("emitting", true); // Workaround for doctool in headless mode, as dummy rasterizer always returns false.
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "amount", PROPERTY_HINT_RANGE, "1,1000000,1,exp"), "set_amount", "get_amount");
 	ADD_PROPERTY(PropertyInfo(Variant::NODE_PATH, "sub_emitter", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "GPUParticles3D"), "set_sub_emitter", "get_sub_emitter");
 	ADD_GROUP("Time", "");

servers/rendering_server.cpp

@@ -2810,6 +2810,12 @@ RenderingServer::RenderingServer() {
 			PropertyInfo(Variant::INT,
 					"rendering/vulkan/rendering/back_end",
 					PROPERTY_HINT_ENUM, "Forward Clustered (Supports Desktop Only),Forward Mobile (Supports Desktop and Mobile)"));
+	// Already defined in RenderingDeviceVulkan::initialize which runs before this code.
+	// We re-define them here just for doctool's sake. Make sure to keep default values in sync.
+	GLOBAL_DEF("rendering/vulkan/staging_buffer/block_size_kb", 256);
+	GLOBAL_DEF("rendering/vulkan/staging_buffer/max_size_mb", 128);
+	GLOBAL_DEF("rendering/vulkan/staging_buffer/texture_upload_region_size_px", 64);
+	GLOBAL_DEF("rendering/vulkan/descriptor_pools/max_descriptors_per_pool", 64);
 
 	GLOBAL_DEF("rendering/3d/viewport/scale", 1.0);
 	ProjectSettings::get_singleton()->set_custom_property_info("rendering/3d/viewport/scale",