Alter definition of IM_UNICODE_ defines to faclitate C-binding. (ocor…

…nut#2538, ocornut#2541, ocornut#2815)

imgui.h

@@ -92,8 +92,6 @@ Index of this file:
 #else
 #define IM_OFFSETOF(_TYPE,_MEMBER)  ((size_t)&(((_TYPE*)0)->_MEMBER))           // Offset of _MEMBER within _TYPE. Old style macro.
 #endif
-#define IM_UNICODE_CODEPOINT_MAX    (sizeof(ImWchar) == 2 ? 0xFFFF : 0x10FFFF)  // Last Unicode code point supported by this build.
-#define IM_UNICODE_CODEPOINT_INVALID 0xFFFD                                     // Standard invalid Unicode code point.
 
 // Warnings
 #if defined(__clang__)
@@ -1652,6 +1650,14 @@ typedef ImGuiInputTextCallbackData  ImGuiTextEditCallbackData;
 // Helpers
 //-----------------------------------------------------------------------------
 
+// Helper: Unicode defines
+#define IM_UNICODE_CODEPOINT_INVALID 0xFFFD     // Invalid Unicode code point (standard value).
+#ifdef IMGUI_USE_WCHAR32
+#define IM_UNICODE_CODEPOINT_MAX     0x10FFFF   // Maximum Unicode code point supported by this build.
+#else
+#define IM_UNICODE_CODEPOINT_MAX     0xFFFF     // Maximum Unicode code point supported by this build.
+#endif
+
 // Helper: Execute a block of code at maximum once a frame. Convenient if you want to quickly create an UI within deep-nested code that runs multiple times every frame.
 // Usage: static ImGuiOnceUponAFrame oaf; if (oaf) ImGui::Text("This will be called only once per frame");
 struct ImGuiOnceUponAFrame