Add native UTF8 support for InputText and remove ImWchar buffer

docs/CHANGELOG.txt

@@ -63,6 +63,10 @@ Other changes:
      #6223, #6364, #6387, #6567, #6692, #6724, #6939, #6984, #7246, #7270, #7375, #7421, #7434,
      #7472, #7581, #7724, #7926, #7937 and probably more..)
 - Nav: pressing any keyboard key while holding Alt disable toggling nav layer on Alt release. (#4439)
+- InputText: internal refactoring to simplify and optimize the code. The ImWchar buffer has been
+  removed. Simplifications allowed to implement new optimizations for handling very large text buffers
+  (e.g. in our testing, handling of a 1 MB text buffer is now 3 times faster in VS2022 Debug build).
+  This is the first step toward more refactorig. (#7925) [@alektron, @ocornut]
 - InputText: added CJK double-width punctuation to list of separators considered for CTRL+Arrow.
 - TextLinkOpenURL(): modified tooltip to display a verb "Open 'xxxx'". (#7885, #7660)
 - Backends: SDL2: use SDL_Vulkan_GetDrawableSize() when available. (#7967, #3190) [@scribam]

docs/TODO.txt

@@ -65,7 +65,6 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - selectable: generic BeginSelectable()/EndSelectable() mechanism. (work out alongside range-select branch)
  - selectable: a way to visualize partial/mixed selection (e.g. parent tree node has children with mixed selection)
 
- - input text: clean up the mess caused by converting UTF-8 <> wchar. the code is rather inefficient right now and super fragile. (WIP branch)
  - input text: preserve scrolling when unfocused?
  - input text: reorganize event handling, allow CharFilter to modify buffers, allow multiple events? (#541)
  - input text: expose CursorPos in char filter event (#816)

imgui.cpp

@@ -1975,7 +1975,7 @@ const char* ImStreolRange(const char* str, const char* str_end)
     return p ? p : str_end;
 }
 
-const ImWchar* ImStrbolW(const ImWchar* buf_mid_line, const ImWchar* buf_begin) // find beginning-of-line
+const char* ImStrbol(const char* buf_mid_line, const char* buf_begin) // find beginning-of-line
 {
     while (buf_mid_line > buf_begin && buf_mid_line[-1] != '\n')
         buf_mid_line--;

imgui.h

@@ -29,7 +29,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM >= 12345')
 #define IMGUI_VERSION       "1.91.2 WIP"
-#define IMGUI_VERSION_NUM   19113
+#define IMGUI_VERSION_NUM   19114
 #define IMGUI_HAS_TABLE
 
 /*

imgui_internal.h

@@ -366,7 +366,7 @@ IMGUI_API const char*   ImStristr(const char* haystack, const char* haystack_end
 IMGUI_API void          ImStrTrimBlanks(char* str);                                         // Remove leading and trailing blanks from a buffer.
 IMGUI_API const char*   ImStrSkipBlank(const char* str);                                    // Find first non-blank character.
 IMGUI_API int           ImStrlenW(const ImWchar* str);                                      // Computer string length (ImWchar string)
-IMGUI_API const ImWchar*ImStrbolW(const ImWchar* buf_mid_line, const ImWchar* buf_begin);   // Find beginning-of-line (ImWchar string)
+IMGUI_API const char*   ImStrbol(const char* buf_mid_line, const char* buf_begin);          // Find beginning-of-line
 IM_MSVC_RUNTIME_CHECKS_OFF
 static inline char      ImToUpper(char c)               { return (c >= 'a' && c <= 'z') ? c &= ~32 : c; }
 static inline bool      ImCharIsBlankA(char c)          { return c == ' ' || c == '\t'; }
@@ -1097,7 +1097,7 @@ struct IMGUI_API ImGuiInputTextDeactivatedState
 #undef IMSTB_TEXTEDIT_STRING
 #undef IMSTB_TEXTEDIT_CHARTYPE
 #define IMSTB_TEXTEDIT_STRING             ImGuiInputTextState
-#define IMSTB_TEXTEDIT_CHARTYPE           ImWchar
+#define IMSTB_TEXTEDIT_CHARTYPE           char
 #define IMSTB_TEXTEDIT_GETWIDTH_NEWLINE   (-1.0f)
 #define IMSTB_TEXTEDIT_UNDOSTATECOUNT     99
 #define IMSTB_TEXTEDIT_UNDOCHARCOUNT      999
@@ -1111,11 +1111,10 @@ struct IMGUI_API ImGuiInputTextState
     ImGuiContext*           Ctx;                    // parent UI context (needs to be set explicitly by parent).
     ImStbTexteditState*     Stb;                    // State for stb_textedit.h
     ImGuiID                 ID;                     // widget id owning the text state
-    int                     CurLenW, CurLenA;       // we need to maintain our buffer length in both UTF-8 and wchar format. UTF-8 length is valid even if TextA is not.
-    ImVector<ImWchar>       TextW;                  // edit buffer, we need to persist but can't guarantee the persistence of the user-provided buffer. so we copy into own buffer.
-    ImVector<char>          TextA;                  // temporary UTF8 buffer for callbacks and other operations. this is not updated in every code-path! size=capacity.
+    int                     CurLenA;                // UTF-8 length of the string in TextA (in bytes)
+    ImVector<char>          TextA;                  // main UTF8 buffer.
     ImVector<char>          InitialTextA;           // value to revert to when pressing Escape = backup of end-user buffer at the time of focus (in UTF-8, unaltered)
-    bool                    TextAIsValid;           // temporary UTF8 buffer is not initially valid before we make the widget active (until then we pull the data from user argument)
+    ImVector<char>          CallbackTextBackup;     // temporary storage for callback to support automatic reconcile of undo-stack
     int                     BufCapacityA;           // end-user buffer capacity
     ImVec2                  Scroll;                 // horizontal offset (managed manually) + vertical scrolling (pulled from child window's own Scroll.y)
     float                   CursorAnim;             // timer for cursor blink, reset on every user action so the cursor reappears immediately
@@ -1129,9 +1128,10 @@ struct IMGUI_API ImGuiInputTextState
 
     ImGuiInputTextState();
     ~ImGuiInputTextState();
-    void        ClearText()                 { CurLenW = CurLenA = 0; TextW[0] = 0; TextA[0] = 0; CursorClamp(); }
-    void        ClearFreeMemory()           { TextW.clear(); TextA.clear(); InitialTextA.clear(); }
+    void        ClearText()                 { CurLenA = 0; TextA[0] = 0; CursorClamp(); }
+    void        ClearFreeMemory()           { TextA.clear(); InitialTextA.clear(); }
     void        OnKeyPressed(int key);      // Cannot be inline because we call in code in stb_textedit.h implementation
+    void        OnCharPressed(unsigned int c);
 
     // Cursor & Selection
     void        CursorAnimReset();