Clarify that IMGUI_USE_BGRA_PACKED_COLOR requires backend support. (#8201)

backends/imgui_impl_dx9.cpp

@@ -4,6 +4,7 @@
 // Implemented features:
 //  [X] Renderer: User texture binding. Use 'LPDIRECT3DTEXTURE9' as ImTextureID. Read the FAQ about ImTextureID!
 //  [X] Renderer: Large meshes support (64k+ vertices) with 16-bit indices.
+//  [X] Renderer: IMGUI_USE_BGRA_PACKED_COLOR is supported, as this is the optimal color encoding for DirectX9.
 
 // You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
 // Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.

backends/imgui_impl_dx9.h

@@ -4,6 +4,7 @@
 // Implemented features:
 //  [X] Renderer: User texture binding. Use 'LPDIRECT3DTEXTURE9' as ImTextureID. Read the FAQ about ImTextureID!
 //  [X] Renderer: Large meshes support (64k+ vertices) with 16-bit indices.
+//  [X] Renderer: IMGUI_USE_BGRA_PACKED_COLOR is supported, as this is the optimal color encoding for DirectX9.
 
 // You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
 // Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.

imconfig.h

@@ -59,7 +59,7 @@
 //#define IMGUI_INCLUDE_IMGUI_USER_H
 //#define IMGUI_USER_H_FILENAME         "my_folder/my_imgui_user.h"
 
-//---- Pack colors to BGRA8 instead of RGBA8 (to avoid converting from one to another)
+//---- Pack vertex colors as BGRA8 instead of RGBA8 (to avoid converting from one to another). Need dedicated backend support.
 //#define IMGUI_USE_BGRA_PACKED_COLOR
 
 //---- Use 32-bit for ImWchar (default is 16-bit) to support Unicode planes 1-16. (e.g. point beyond 0xFFFF like emoticons, dingbats, symbols, shapes, ancient languages, etc...)

imgui.h

@@ -2715,7 +2715,8 @@ IM_MSVC_RUNTIME_CHECKS_RESTORE
 #endif
 
 // Helpers macros to generate 32-bit encoded colors
-// User can declare their own format by #defining the 5 _SHIFT/_MASK macros in their imconfig file.
+// - User can declare their own format by #defining the 5 _SHIFT/_MASK macros in their imconfig file.
+// - Any setting other than the default will need custom backend support. The only standard backend that supports anything else than the default is DirectX9.
 #ifndef IM_COL32_R_SHIFT
 #ifdef IMGUI_USE_BGRA_PACKED_COLOR
 #define IM_COL32_R_SHIFT    16