Introduce IMGUI_USE_BGRA_PACKED_COLOR in imconfig.h.

When IMGUI_USE_BGRA_PACKED_COLOR is defined packed color hold in ImU32 use BGRA format instead RGBA.

imconfig.h

@@ -26,6 +26,9 @@
 //---- Don't define obsolete functions names
 //#define IMGUI_DISABLE_OBSOLETE_FUNCTIONS
 
+//---- Pack colors to BGRA instead of RGBA (remove need to post process vertex buffer in back ends)
+//#define IMGUI_USE_BGRA_PACKED_COLOR
+
 //---- Implement STB libraries in a namespace to avoid conflicts
 //#define IMGUI_STB_NAMESPACE     ImGuiStb
 

imgui.cpp

@@ -1195,16 +1195,20 @@ int ImTextCountUtf8BytesFromStr(const ImWchar* in_text, const ImWchar* in_text_e
 ImVec4 ImGui::ColorConvertU32ToFloat4(ImU32 in)
 {
     float s = 1.0f/255.0f;
-    return ImVec4((in & 0xFF) * s, ((in >> 8) & 0xFF) * s, ((in >> 16) & 0xFF) * s, (in >> 24) * s);
+    return ImVec4(
+        ((in >> IM_COL32_R_SHIFT) & 0xFF) * s,
+        ((in >> IM_COL32_G_SHIFT) & 0xFF) * s,
+        ((in >> IM_COL32_B_SHIFT) & 0xFF) * s,
+        ((in >> IM_COL32_A_SHIFT) & 0xFF) * s);
 }
 
 ImU32 ImGui::ColorConvertFloat4ToU32(const ImVec4& in)
 {
     ImU32 out;
-    out  = ((ImU32)IM_F32_TO_INT8_SAT(in.x));
-    out |= ((ImU32)IM_F32_TO_INT8_SAT(in.y)) << 8;
-    out |= ((ImU32)IM_F32_TO_INT8_SAT(in.z)) << 16;
-    out |= ((ImU32)IM_F32_TO_INT8_SAT(in.w)) << 24;
+    out  = ((ImU32)IM_F32_TO_INT8_SAT(in.x)) << IM_COL32_R_SHIFT;
+    out |= ((ImU32)IM_F32_TO_INT8_SAT(in.y)) << IM_COL32_G_SHIFT;
+    out |= ((ImU32)IM_F32_TO_INT8_SAT(in.z)) << IM_COL32_B_SHIFT;
+    out |= ((ImU32)IM_F32_TO_INT8_SAT(in.w)) << IM_COL32_A_SHIFT;
     return out;
 }
 

imgui.h

@@ -1091,7 +1091,18 @@ struct ImGuiListClipper
 //-----------------------------------------------------------------------------
 
 // Helpers macros to generate 32-bits encoded colors
-#define IM_COL32(R,G,B,A)    (((ImU32)(A)<<24) | ((ImU32)(B)<<16) | ((ImU32)(G)<<8) | ((ImU32)(R)))
+#ifdef IMGUI_USE_BGRA_PACKED_COLOR
+#define IM_COL32_R_SHIFT    16
+#define IM_COL32_G_SHIFT    8
+#define IM_COL32_B_SHIFT    0
+#define IM_COL32_A_SHIFT    24
+#else
+#define IM_COL32_R_SHIFT    0
+#define IM_COL32_G_SHIFT    8
+#define IM_COL32_B_SHIFT    16
+#define IM_COL32_A_SHIFT    24
+#endif
+#define IM_COL32(R,G,B,A)    (((ImU32)(A)<<IM_COL32_A_SHIFT) | ((ImU32)(B)<<IM_COL32_B_SHIFT) | ((ImU32)(G)<<IM_COL32_G_SHIFT) | ((ImU32)(R)<<IM_COL32_R_SHIFT))
 #define IM_COL32_WHITE       (0xFFFFFFFF)
 #define IM_COL32_BLACK       (0xFF000000)
 #define IM_COL32_BLACK_TRANS (0x00000000)    // Transparent black