Add VOLK_NAMESPACE configuration to use C++ namespaces

In some cases the use of global vk* symbols is inconvenient, as it can
conflict with vk* functions defined by the loader; generally speaking
this should not be required, but some dynamic library cases are
difficult to support cleanly.

This problem can be solved when C++ is available: by building volk.h/c
as C++ and wrapping functions in volk namespace, which is automatically
used, the compiler can still find the functions so no change in source
code is necessary, but the global symbols get C++ mangling that never
overlaps with vk*.

This is not designed as a main mode of operation, but it can be useful
when the default setup doesn't fully work.

Author: zeux

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.5...3.30)
 
-project(volk VERSION 
+project(volk VERSION
 # VOLK_GENERATE_VERSION
 304
 # VOLK_GENERATE_VERSION
@@ -18,6 +18,9 @@ endif()
 if(NOT DEFINED VOLK_INSTALL)
   option(VOLK_INSTALL "Create installation targets" OFF)
 endif()
+if(NOT DEFINED VOLK_NAMESPACE)
+  option(VOLK_NAMESPACE "Use C++ namespace for vk* functions" OFF)
+endif()
 if(NOT DEFINED VOLK_HEADERS_ONLY)
   option(VOLK_HEADERS_ONLY "Add interface library only" OFF)
 endif()
@@ -35,6 +38,10 @@ if(NOT VOLK_HEADERS_ONLY OR VOLK_INSTALL)
     $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>
     $<INSTALL_INTERFACE:include>
   )
+  if(VOLK_NAMESPACE)
+    target_compile_definitions(volk PUBLIC VOLK_NAMESPACE)
+    set_source_files_properties(volk.c PROPERTIES LANGUAGE CXX)
+  endif()
   if(VOLK_STATIC_DEFINES)
     target_compile_definitions(volk PUBLIC ${VOLK_STATIC_DEFINES})
   endif()

volk.c

@@ -22,8 +22,12 @@
 #endif
 
 #ifdef __cplusplus
+#ifdef VOLK_NAMESPACE
+namespace volk {
+#else
 extern "C" {
 #endif
+#endif
 
 #ifdef _WIN32
 __declspec(dllimport) HMODULE __stdcall LoadLibraryA(LPCSTR);
@@ -3360,6 +3364,6 @@ PFN_vkAcquireNextImage2KHR vkAcquireNextImage2KHR;
 #endif
 
 #ifdef __cplusplus
-}
+} // extern "C" / namespace volk
 #endif
 /* clang-format on */

volk.h

@@ -10,6 +10,10 @@
 #ifndef VOLK_H_
 #define VOLK_H_
 
+#if defined(VOLK_NAMESPACE) && !defined(__cplusplus)
+#error VOLK_NAMESPACE is only supported in C++
+#endif
+
 #if defined(VULKAN_H_) && !defined(VK_NO_PROTOTYPES)
 #	error To use volk, you need to define VK_NO_PROTOTYPES before including vulkan.h
 #endif
@@ -52,8 +56,12 @@
 #endif
 
 #ifdef __cplusplus
+#ifdef VOLK_NAMESPACE
+namespace volk {
+#else
 extern "C" {
 #endif
+#endif
 
 struct VolkDeviceTable;
 
@@ -2140,11 +2148,15 @@ extern PFN_vkAcquireNextImage2KHR vkAcquireNextImage2KHR;
 /* VOLK_GENERATE_PROTOTYPES_H */
 
 #ifdef __cplusplus
-}
+} // extern "C" / namespace volk
 #endif
 
+#ifdef VOLK_NAMESPACE
+using namespace volk;
 #endif
 
+#endif // VOLK_H
+
 #ifdef VOLK_IMPLEMENTATION
 #undef VOLK_IMPLEMENTATION
 /* Prevent tools like dependency checkers from detecting a cyclic dependency */