Add ability to use extension dispatch table when missing extensions (#56)

* add ability to use extension dispatch table when some extensions aren't present

* add d3d11 extension stub

Author: chrisfromwork

shared/XrUtility/XrExtensions.h

@@ -15,23 +15,44 @@
 //*********************************************************
 #pragma once
 
-#define FOR_EACH_EXTENSION_FUNCTION(_)           \
-    _(xrCreateSpatialAnchorMSFT)                 \
-    _(xrCreateSpatialAnchorSpaceMSFT)            \
-    _(xrDestroySpatialAnchorMSFT)                \
-    _(xrCreateHandTrackerEXT)                    \
-    _(xrDestroyHandTrackerEXT)                   \
-    _(xrLocateHandJointsEXT)                     \
-    _(xrCreateHandMeshSpaceMSFT)                 \
-    _(xrUpdateHandMeshMSFT)                      \
-    _(xrConvertWin32PerformanceCounterToTimeKHR) \
-    _(xrCreateSpatialGraphNodeSpaceMSFT)         \
-    _(xrGetD3D11GraphicsRequirementsKHR)         \
+#ifdef XR_USE_PLATFORM_WIN32
+#define FOR_EACH_WIN32_EXTENSION_FUNCTION(_) \
+    _(xrConvertWin32PerformanceCounterToTimeKHR)
+#else
+#define FOR_EACH_WIN32_EXTENSION_FUNCTION(_)
+#endif
+
+#ifdef XR_USE_GRAPHICS_API_D3D11
+#define FOR_EACH_D3D11_EXTENSION_FUNCTION(_) \
+    _(xrGetD3D11GraphicsRequirementsKHR)
+#else
+#define FOR_EACH_D3D11_EXTENSION_FUNCTION(_)
+#endif
+
+#ifdef XR_MSFT_CONTROLLER_MODEL_PREVIEW_EXTENSION_NAME
+#define FOR_EACH_CONTROLLER_MODEL_EXTENSION_FUNCTION(_) \
     _(xrGetControllerModelKeyMSFT)               \
     _(xrLoadControllerModelMSFT)                 \
     _(xrGetControllerModelPropertiesMSFT)        \
-    _(xrGetControllerModelStateMSFT)             \
-    _(xrGetVisibilityMaskKHR)
+    _(xrGetControllerModelStateMSFT)
+#else
+#define FOR_EACH_CONTROLLER_MODEL_EXTENSION_FUNCTION(_)
+#endif
+
+#define FOR_EACH_EXTENSION_FUNCTION(_)              \
+    _(xrCreateSpatialAnchorMSFT)                    \
+    _(xrCreateSpatialAnchorSpaceMSFT)               \
+    _(xrDestroySpatialAnchorMSFT)                   \
+    _(xrCreateHandTrackerEXT)                       \
+    _(xrDestroyHandTrackerEXT)                      \
+    _(xrLocateHandJointsEXT)                        \
+    _(xrCreateHandMeshSpaceMSFT)                    \
+    _(xrUpdateHandMeshMSFT)                         \
+    _(xrCreateSpatialGraphNodeSpaceMSFT)            \
+    _(xrGetVisibilityMaskKHR)                       \
+    FOR_EACH_WIN32_EXTENSION_FUNCTION(_)            \
+    FOR_EACH_D3D11_EXTENSION_FUNCTION(_)            \
+    FOR_EACH_CONTROLLER_MODEL_EXTENSION_FUNCTION(_)
 
 #define GET_INSTANCE_PROC_ADDRESS(name) \
     (void)xrGetInstanceProcAddr(instance, #name, reinterpret_cast<PFN_xrVoidFunction*>(const_cast<PFN_##name*>(&name)));