renderer: stub vulkan build

Still relies on OpenGL for everything, but report the required build-time toggle for a Vulkan build.

Author: illwieckz

src/engine/renderer/tr_init.cpp

@@ -44,6 +44,16 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 
 	static void GfxInfo_f();
 
+#if defined(DAEMON_RENDERER_OPENGL)
+	constexpr rendererApi_t rendererApi = rendererApi_t::OPENGL;
+#elif defined(DAEMON_RENDERER_VULKAN)
+	constexpr rendererApi_t rendererApi = rendererApi_t::VULKAN;
+#else
+	#error Undefined renderer API.
+#endif
+
+Cvar::Cvar<int> r_rendererApi( "r_rendererApi", "Renderer API: 0: OpenGL, 1: Vulkan", Cvar::ROM, Util::ordinal( rendererApi ) );
+
 	cvar_t      *r_glMajorVersion;
 	cvar_t      *r_glMinorVersion;
 	cvar_t      *r_glProfile;

src/engine/renderer/tr_local.h

@@ -340,6 +340,12 @@ enum class ssaoMode {
 	  RSPEEDS_NEAR_FAR,
 	};
 
+	enum class rendererApi_t
+	{
+		OPENGL,
+		VULKAN,
+	};
+
 	enum class glDebugModes_t
 	{
 		GLDEBUG_NONE,
@@ -2834,6 +2840,8 @@ enum class ssaoMode {
 //
 // cvars
 //
+	extern Cvar::Range<Cvar::Cvar<int>> r_rendererAPI;
+
 	extern cvar_t *r_glMajorVersion; // override GL version autodetect (for testing)
 	extern cvar_t *r_glMinorVersion;
 	extern cvar_t *r_glProfile;