InputText: Clarified comments around ImGuiInputTextFlags_CallbackResize and other callbacks. (#2006, #1443, #1008)

imgui.h

@@ -656,10 +656,10 @@ enum ImGuiInputTextFlags_
     ImGuiInputTextFlags_CharsNoBlank        = 1 << 3,   // Filter out spaces, tabs
     ImGuiInputTextFlags_AutoSelectAll       = 1 << 4,   // Select entire text when first taking mouse focus
     ImGuiInputTextFlags_EnterReturnsTrue    = 1 << 5,   // Return 'true' when Enter is pressed (as opposed to when the value was modified)
-    ImGuiInputTextFlags_CallbackCompletion  = 1 << 6,   // Call user function on pressing TAB (for completion handling)
-    ImGuiInputTextFlags_CallbackHistory     = 1 << 7,   // Call user function on pressing Up/Down arrows (for history handling)
-    ImGuiInputTextFlags_CallbackAlways      = 1 << 8,   // Call user function every time. User code may query cursor position, modify text buffer.
-    ImGuiInputTextFlags_CallbackCharFilter  = 1 << 9,   // Call user function to filter character. Modify data->EventChar to replace/filter input, or return 1 in callback to discard character.
+    ImGuiInputTextFlags_CallbackCompletion  = 1 << 6,   // Callback on pressing TAB (for completion handling)
+    ImGuiInputTextFlags_CallbackHistory     = 1 << 7,   // Callback on pressing Up/Down arrows (for history handling)
+    ImGuiInputTextFlags_CallbackAlways      = 1 << 8,   // Callback on each iteration. User code may query cursor position, modify text buffer.
+    ImGuiInputTextFlags_CallbackCharFilter  = 1 << 9,   // Callback on character inputs to replace or discard them. Modify 'EventChar' to replace or discard, or return 1 in callback to discard.
     ImGuiInputTextFlags_AllowTabInput       = 1 << 10,  // Pressing TAB input a '\t' character into the text field
     ImGuiInputTextFlags_CtrlEnterForNewLine = 1 << 11,  // In multi-line mode, unfocus with Enter, add new line with Ctrl+Enter (default is opposite: unfocus with Ctrl+Enter, add line with Enter).
     ImGuiInputTextFlags_NoHorizontalScroll  = 1 << 12,  // Disable following the cursor horizontally
@@ -668,7 +668,7 @@ enum ImGuiInputTextFlags_
     ImGuiInputTextFlags_Password            = 1 << 15,  // Password mode, display all characters as '*'
     ImGuiInputTextFlags_NoUndoRedo          = 1 << 16,  // Disable undo/redo. Note that input text owns the text data while active, if you want to provide your own undo/redo stack you need e.g. to call ClearActiveID().
     ImGuiInputTextFlags_CharsScientific     = 1 << 17,  // Allow 0123456789.+-*/eE (Scientific notation input)
-    ImGuiInputTextFlags_CallbackResize      = 1 << 18,  // Allow buffer capacity resize + notify when the string wants to be resized (for string types which hold a cache of their Size) (see misc/stl/imgui_stl.h for an example of using this)
+    ImGuiInputTextFlags_CallbackResize      = 1 << 18,  // Callback on buffer capacity changes request (beyond 'buf_size' parameter value), allowing the string to grow. Notify when the string wants to be resized (for string types which hold a cache of their Size). You will be provided a new BufSize in the callback and NEED to honor it. (see misc/stl/imgui_stl.h for an example of using this)
     // [Internal]
     ImGuiInputTextFlags_Multiline           = 1 << 20   // For internal use by InputTextMultiline()
 };
@@ -1437,9 +1437,12 @@ struct ImGuiStorage
 
 // Shared state of InputText(), passed as an argument to your callback when a ImGuiInputTextFlags_Callback* flag is used.
 // The callback function should return 0 by default.
-// Special processing:
-// - ImGuiInputTextFlags_CallbackCharFilter:  return 1 if the character is not allowed. You may also set 'EventChar=0' as any character replacement are allowed.
-// - ImGuiInputTextFlags_CallbackResize:      notified by InputText() when the string is resized. BufTextLen is set to the new desired string length so you can update the string size on your side of the fence. You can also replace Buf pointer if your underlying data is reallocated. No need to initialize new characters or zero-terminator as InputText will do it right after the resize callback.
+// Callbacks (follow a flag name and see comments in ImGuiInputTextFlags_ declarations for more details)
+// - ImGuiInputTextFlags_CallbackCompletion:  Callback on pressing TAB
+// - ImGuiInputTextFlags_CallbackHistory:     Callback on pressing Up/Down arrows
+// - ImGuiInputTextFlags_CallbackAlways:      Callback on each iteration
+// - ImGuiInputTextFlags_CallbackCharFilter:  Callback on character inputs to replace or discard them. Modify 'EventChar' to replace or discard, or return 1 in callback to discard.
+// - ImGuiInputTextFlags_CallbackResize:      Callback on buffer capacity changes request (beyond 'buf_size' parameter value), allowing the string to grow. 
 struct ImGuiInputTextCallbackData
 {
     ImGuiInputTextFlags EventFlag;      // One ImGuiInputTextFlags_Callback*    // Read-only
@@ -1449,12 +1452,12 @@ struct ImGuiInputTextCallbackData
     // Arguments for the different callback events
     // - To modify the text buffer in a callback, prefer using the InsertChars() / DeleteChars() function. InsertChars() will take care of calling the resize callback if necessary.
     // - If you know your edits are not going to resize the underlying buffer allocation, you may modify the contents of 'Buf[]' directly. You need to update 'BufTextLen' accordingly (0 <= BufTextLen < BufSize) and set 'BufDirty'' to true so InputText can update its internal state.
-    ImWchar             EventChar;      // Character input                      // Read-write   // [CharFilter] Replace character or set to zero. return 1 is equivalent to setting EventChar=0;
+    ImWchar             EventChar;      // Character input                      // Read-write   // [CharFilter] Replace character with another one, or set to zero to drop. return 1 is equivalent to setting EventChar=0;
     ImGuiKey            EventKey;       // Key pressed (Up/Down/TAB)            // Read-only    // [Completion,History]
     char*               Buf;            // Text buffer                          // Read-write   // [Resize] Can replace pointer / [Completion,History,Always] Only write to pointed data, don't replace the actual pointer!
-    int                 BufTextLen;     // Text length in bytes                 // Read-write   // [Resize,Completion,History,Always] Exclude zero-terminator storage. In C land: == strlen(some_text), in C++ land: string.length()
-    int                 BufSize;        // Buffer capacity in bytes             // Read-only    // [Resize,Completion,History,Always] Include zero-terminator storage. In C land == ARRAYSIZE(my_char_array), in C++ land: string.capacity()+1
-    bool                BufDirty;       // Set if you modify Buf/BufTextLen!!   // Write        // [Completion,History,Always]
+    int                 BufTextLen;     // Text length (in bytes)               // Read-write   // [Resize,Completion,History,Always] Exclude zero-terminator storage. In C land: == strlen(some_text), in C++ land: string.length()
+    int                 BufSize;        // Buffer size (in bytes) = capacity+1  // Read-only    // [Resize,Completion,History,Always] Include zero-terminator storage. In C land == ARRAYSIZE(my_char_array), in C++ land: string.capacity()+1
+    bool                BufDirty;       // Set if you modify Buf/BufTextLen!    // Write        // [Completion,History,Always]
     int                 CursorPos;      //                                      // Read-write   // [Completion,History,Always]
     int                 SelectionStart; //                                      // Read-write   // [Completion,History,Always] == to SelectionEnd when no selection)
     int                 SelectionEnd;   //                                      // Read-write   // [Completion,History,Always]

misc/stl/imgui_stl.cpp

@@ -22,6 +22,7 @@ static int InputTextCallback(ImGuiInputTextCallbackData* data)
     if (data->EventFlag == ImGuiInputTextFlags_CallbackResize)
     {
         // Resize string callback
+        // If for some reason we refuse the new length (BufTextLen) and/or capacity (BufSize) we need to set them back to what we want.
         std::string* str = user_data->Str;
         IM_ASSERT(data->Buf == str->c_str());
         str->resize(data->BufTextLen);