Remove Vulkan SDK build dependency by bundling Vulkan headers

The Vulkan backend already uses VK_NO_PROTOTYPES + dynamic dispatch
(vulkan.hpp dispatcher bootstrapped from SDL), so the link to
Vulkan::Vulkan was unused. Replace find_package(Vulkan) with bundled
Vulkan-Headers (v1.4.309) for both code and imgui targets. Make imgui
compile with VK_NO_PROTOTYPES (PUBLIC) and load its Vulkan function
pointers via ImGui_ImplVulkan_LoadFunctions() at init time.

Author: laanwj

code/CMakeLists.txt

@@ -113,16 +113,8 @@ if (FSO_BUILD_WITH_OPENGL)
 	target_compile_definitions(code PUBLIC WITH_OPENGL)
 endif()
 if (FSO_BUILD_WITH_VULKAN)
-	find_package(Vulkan REQUIRED)
-	if (Vulkan_FOUND)
-		target_compile_definitions(code PUBLIC WITH_VULKAN)
-		target_link_libraries(code PRIVATE Vulkan::Vulkan)
-
-		target_compile_definitions(code PUBLIC WITH_VULKAN VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=1 VK_NO_PROTOTYPES)
-	else()
-		message(WARNING "FSO_BUILD_WITH_VULKAN was set, but the package was unable to be found. Forcing OFF.")
-		set(FSO_BUILD_WITH_VULKAN OFF CACHE BOOL "Enable compilation of the Vulkan renderer" FORCE)
-	endif()
+	target_compile_definitions(code PUBLIC WITH_VULKAN VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=1 VK_NO_PROTOTYPES)
+	target_link_libraries(code PUBLIC VulkanHeaders)
 endif()
 
 include(shaders.cmake)

code/graphics/vulkan/VulkanRenderer.cpp

@@ -1501,6 +1501,13 @@ void VulkanRenderer::initImGui()
 {
 	createImGuiDescriptorPool();
 
+	// Load Vulkan function pointers for imgui (required with VK_NO_PROTOTYPES)
+	auto vkInstance = static_cast<VkInstance>(*m_vkInstance);
+	ImGui_ImplVulkan_LoadFunctions([](const char* function_name, void* user_data) -> PFN_vkVoidFunction {
+		return VULKAN_HPP_DEFAULT_DISPATCHER.vkGetInstanceProcAddr(
+			static_cast<VkInstance>(user_data), function_name);
+	}, vkInstance);
+
 	ImGui_ImplVulkan_InitInfo initInfo = {};
 	initInfo.Instance = static_cast<VkInstance>(*m_vkInstance);
 	initInfo.PhysicalDevice = static_cast<VkPhysicalDevice>(m_physicalDevice);

lib/CMakeLists.txt

@@ -45,6 +45,10 @@ include(antlr4.cmake)
 
 include(vulkan.cmake)
 
+if (FSO_BUILD_WITH_VULKAN)
+	add_subdirectory(vulkan-headers)
+endif()
+
 add_subdirectory(mdns)
 
 add_subdirectory(accidental-noise)

lib/imgui/CMakeLists.txt

@@ -39,7 +39,7 @@ TARGET_LINK_LIBRARIES(imgui PUBLIC sdl2)
 target_link_libraries(imgui PUBLIC compiler)
 
 if (FSO_BUILD_WITH_VULKAN)
-	find_package(Vulkan REQUIRED)
-    target_compile_definitions(imgui INTERFACE VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=1 VK_NO_PROTOTYPES)
-	target_link_libraries(imgui PRIVATE Vulkan::Vulkan)
+	target_compile_definitions(imgui PUBLIC VK_NO_PROTOTYPES)
+	target_compile_definitions(imgui INTERFACE VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=1)
+	target_link_libraries(imgui PUBLIC VulkanHeaders)
 endif()

lib/vulkan-headers/CMakeLists.txt

@@ -0,0 +1,4 @@
+add_library(VulkanHeaders INTERFACE)
+target_include_directories(VulkanHeaders SYSTEM INTERFACE
+    "${CMAKE_CURRENT_SOURCE_DIR}/include"
+)