ThirdPartyLibs/imgui/stb_textedit.h

// [ImGui] this is a slightly modified version of stb_truetype.h 1.9. Those changes would need to be pushed into nothings/sb
// [ImGui] - fixed linestart handler when over last character of multi-line buffer + simplified existing code (#588, #815)
// [ImGui] - fixed a state corruption/crash bug in stb_text_redo and stb_textedit_discard_redo (#715)
// [ImGui] - fixed a crash bug in stb_textedit_discard_redo (#681)
// [ImGui] - fixed some minor warnings

// stb_textedit.h - v1.9  - public domain - Sean Barrett
// Development of this library was sponsored by RAD Game Tools
//
// This C header file implements the guts of a multi-line text-editing
// widget; you implement display, word-wrapping, and low-level string
// insertion/deletion, and stb_textedit will map user inputs into
// insertions & deletions, plus updates to the cursor position,
// selection state, and undo state.
//
// It is intended for use in games and other systems that need to build
// their own custom widgets and which do not have heavy text-editing
// requirements (this library is not recommended for use for editing large
// texts, as its performance does not scale and it has limited undo).
//
// Non-trivial behaviors are modelled after Windows text controls.
//
//
// LICENSE
//
//   This software is dual-licensed to the public domain and under the following
//   license: you are granted a perpetual, irrevocable license to copy, modify,
//   publish, and distribute this file as you see fit.
//
//
// DEPENDENCIES
//
// Uses the C runtime function 'memmove', which you can override
// by defining STB_TEXTEDIT_memmove before the implementation.
// Uses no other functions. Performs no runtime allocations.
//
//
// VERSION HISTORY
//
//   1.9  (2016-08-27) customizable move-by-word
//   1.8  (2016-04-02) better keyboard handling when mouse button is down
//   1.7  (2015-09-13) change y range handling in case baseline is non-0
//   1.6  (2015-04-15) allow STB_TEXTEDIT_memmove
//   1.5  (2014-09-10) add support for secondary keys for OS X
//   1.4  (2014-08-17) fix signed/unsigned warnings
//   1.3  (2014-06-19) fix mouse clicking to round to nearest char boundary
//   1.2  (2014-05-27) fix some RAD types that had crept into the new code
//   1.1  (2013-12-15) move-by-word (requires STB_TEXTEDIT_IS_SPACE )
//   1.0  (2012-07-26) improve documentation, initial public release
//   0.3  (2012-02-24) bugfixes, single-line mode; insert mode
//   0.2  (2011-11-28) fixes to undo/redo
//   0.1  (2010-07-08) initial version
//
// ADDITIONAL CONTRIBUTORS
//
//   Ulf Winklemann: move-by-word in 1.1
//   Fabian Giesen: secondary key inputs in 1.5
//   Martins Mozeiko: STB_TEXTEDIT_memmove
//
//   Bugfixes:
//      Scott Graham
//      Daniel Keller
//      Omar Cornut
//
// USAGE
//
// This file behaves differently depending on what symbols you define
// before including it.
//
//
// Header-file mode:
//
//   If you do not define STB_TEXTEDIT_IMPLEMENTATION before including this,
//   it will operate in "header file" mode. In this mode, it declares a
//   single public symbol, STB_TexteditState, which encapsulates the current
//   state of a text widget (except for the string, which you will store
//   separately).
//
//   To compile in this mode, you must define STB_TEXTEDIT_CHARTYPE to a
//   primitive type that defines a single character (e.g. char, wchar_t, etc).
//
//   To save space or increase undo-ability, you can optionally define the
//   following things that are used by the undo system:
//
//      STB_TEXTEDIT_POSITIONTYPE         small int type encoding a valid cursor position
//      STB_TEXTEDIT_UNDOSTATECOUNT       the number of undo states to allow
//      STB_TEXTEDIT_UNDOCHARCOUNT        the number of characters to store in the undo buffer
//
//   If you don't define these, they are set to permissive types and
//   moderate sizes. The undo system does no memory allocations, so
//   it grows STB_TexteditState by the worst-case storage which is (in bytes):
//
//        [4 + sizeof(STB_TEXTEDIT_POSITIONTYPE)] * STB_TEXTEDIT_UNDOSTATE_COUNT
//      +      sizeof(STB_TEXTEDIT_CHARTYPE)      * STB_TEXTEDIT_UNDOCHAR_COUNT
//
//
// Implementation mode:
//
//   If you define STB_TEXTEDIT_IMPLEMENTATION before including this, it
//   will compile the implementation of the text edit widget, depending
//   on a large number of symbols which must be defined before the include.
//
//   The implementation is defined only as static functions. You will then
//   need to provide your own APIs in the same file which will access the
//   static functions.
//
//   The basic concept is that you provide a "string" object which
//   behaves like an array of characters. stb_textedit uses indices to
//   refer to positions in the string, implicitly representing positions
//   in the displayed textedit. This is true for both plain text and
//   rich text; even with rich text stb_truetype interacts with your
//   code as if there was an array of all the displayed characters.
//
// Symbols that must be the same in header-file and implementation mode:
//
//     STB_TEXTEDIT_CHARTYPE             the character type
//     STB_TEXTEDIT_POSITIONTYPE         small type that a valid cursor position
//     STB_TEXTEDIT_UNDOSTATECOUNT       the number of undo states to allow
//     STB_TEXTEDIT_UNDOCHARCOUNT        the number of characters to store in the undo buffer
//
// Symbols you must define for implementation mode:
//
//    STB_TEXTEDIT_STRING               the type of object representing a string being edited,
//                                      typically this is a wrapper object with other data you need
//
//    STB_TEXTEDIT_STRINGLEN(obj)       the length of the string (ideally O(1))
//    STB_TEXTEDIT_LAYOUTROW(&r,obj,n)  returns the results of laying out a line of characters
//                                        starting from character #n (see discussion below)
//    STB_TEXTEDIT_GETWIDTH(obj,n,i)    returns the pixel delta from the xpos of the i'th character
//                                        to the xpos of the i+1'th char for a line of characters
//                                        starting at character #n (i.e. accounts for kerning
//                                        with previous char)
//    STB_TEXTEDIT_KEYTOTEXT(k)         maps a keyboard input to an insertable character
//                                        (return type is int, -1 means not valid to insert)
//    STB_TEXTEDIT_GETCHAR(obj,i)       returns the i'th character of obj, 0-based
//    STB_TEXTEDIT_NEWLINE              the character returned by _GETCHAR() we recognize
//                                        as manually wordwrapping for end-of-line positioning
//
//    STB_TEXTEDIT_DELETECHARS(obj,i,n)      delete n characters starting at i
//    STB_TEXTEDIT_INSERTCHARS(obj,i,c*,n)   insert n characters at i (pointed to by STB_TEXTEDIT_CHARTYPE*)
//
//    STB_TEXTEDIT_K_SHIFT       a power of two that is or'd in to a keyboard input to represent the shift key
//
//    STB_TEXTEDIT_K_LEFT        keyboard input to move cursor left
//    STB_TEXTEDIT_K_RIGHT       keyboard input to move cursor right
//    STB_TEXTEDIT_K_UP          keyboard input to move cursor up
//    STB_TEXTEDIT_K_DOWN        keyboard input to move cursor down
//    STB_TEXTEDIT_K_LINESTART   keyboard input to move cursor to start of line  // e.g. HOME
//    STB_TEXTEDIT_K_LINEEND     keyboard input to move cursor to end of line    // e.g. END
//    STB_TEXTEDIT_K_TEXTSTART   keyboard input to move cursor to start of text  // e.g. ctrl-HOME
//    STB_TEXTEDIT_K_TEXTEND     keyboard input to move cursor to end of text    // e.g. ctrl-END
//    STB_TEXTEDIT_K_DELETE      keyboard input to delete selection or character under cursor
//    STB_TEXTEDIT_K_BACKSPACE   keyboard input to delete selection or character left of cursor
//    STB_TEXTEDIT_K_UNDO        keyboard input to perform undo
//    STB_TEXTEDIT_K_REDO        keyboard input to perform redo
//
// Optional:
//    STB_TEXTEDIT_K_INSERT              keyboard input to toggle insert mode
//    STB_TEXTEDIT_IS_SPACE(ch)          true if character is whitespace (e.g. 'isspace'),
//                                          required for default WORDLEFT/WORDRIGHT handlers
//    STB_TEXTEDIT_MOVEWORDLEFT(obj,i)   custom handler for WORDLEFT, returns index to move cursor to
//    STB_TEXTEDIT_MOVEWORDRIGHT(obj,i)  custom handler for WORDRIGHT, returns index to move cursor to
//    STB_TEXTEDIT_K_WORDLEFT            keyboard input to move cursor left one word // e.g. ctrl-LEFT
//    STB_TEXTEDIT_K_WORDRIGHT           keyboard input to move cursor right one word // e.g. ctrl-RIGHT
//    STB_TEXTEDIT_K_LINESTART2          secondary keyboard input to move cursor to start of line
//    STB_TEXTEDIT_K_LINEEND2            secondary keyboard input to move cursor to end of line
//    STB_TEXTEDIT_K_TEXTSTART2          secondary keyboard input to move cursor to start of text
//    STB_TEXTEDIT_K_TEXTEND2            secondary keyboard input to move cursor to end of text
//
// Todo:
//    STB_TEXTEDIT_K_PGUP        keyboard input to move cursor up a page
//    STB_TEXTEDIT_K_PGDOWN      keyboard input to move cursor down a page
//
// Keyboard input must be encoded as a single integer value; e.g. a character code
// and some bitflags that represent shift states. to simplify the interface, SHIFT must
// be a bitflag, so we can test the shifted state of cursor movements to allow selection,
// i.e. (STB_TEXTED_K_RIGHT|STB_TEXTEDIT_K_SHIFT) should be shifted right-arrow.
//
// You can encode other things, such as CONTROL or ALT, in additional bits, and
// then test for their presence in e.g. STB_TEXTEDIT_K_WORDLEFT. For example,
// my Windows implementations add an additional CONTROL bit, and an additional KEYDOWN
// bit. Then all of the STB_TEXTEDIT_K_ values bitwise-or in the KEYDOWN bit,
// and I pass both WM_KEYDOWN and WM_CHAR events to the "key" function in the
// API below. The control keys will only match WM_KEYDOWN events because of the
// keydown bit I add, and STB_TEXTEDIT_KEYTOTEXT only tests for the KEYDOWN
// bit so it only decodes WM_CHAR events.
//
// STB_TEXTEDIT_LAYOUTROW returns information about the shape of one displayed
// row of characters assuming they start on the i'th character--the width and
// the height and the number of characters consumed. This allows this library
// to traverse the entire layout incrementally. You need to compute word-wrapping
// here.
//
// Each textfield keeps its own insert mode state, which is not how normal
// applications work. To keep an app-wide insert mode, update/copy the
// "insert_mode" field of STB_TexteditState before/after calling API functions.
//
// API
//
//    void stb_textedit_initialize_state(STB_TexteditState *state, int is_single_line)
//
//    void stb_textedit_click(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, float x, float y)
//    void stb_textedit_drag(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, float x, float y)
//    int  stb_textedit_cut(STB_TEXTEDIT_STRING *str, STB_TexteditState *state)
//    int  stb_textedit_paste(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, STB_TEXTEDIT_CHARTYPE *text, int len)
//    void stb_textedit_key(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, int key)
//
//    Each of these functions potentially updates the string and updates the
//    state.
//
//      initialize_state:
//          set the textedit state to a known good default state when initially
//          constructing the textedit.
//
//      click:
//          call this with the mouse x,y on a mouse down; it will update the cursor
//          and reset the selection start/end to the cursor point. the x,y must
//          be relative to the text widget, with (0,0) being the top left.
//
//      drag:
//          call this with the mouse x,y on a mouse drag/up; it will update the
//          cursor and the selection end point
//
//      cut:
//          call this to delete the current selection; returns true if there was
//          one. you should FIRST copy the current selection to the system paste buffer.
//          (To copy, just copy the current selection out of the string yourself.)
//
//      paste:
//          call this to paste text at the current cursor point or over the current
//          selection if there is one.
//
//      key:
//          call this for keyboard inputs sent to the textfield. you can use it
//          for "key down" events or for "translated" key events. if you need to
//          do both (as in Win32), or distinguish Unicode characters from control
//          inputs, set a high bit to distinguish the two; then you can define the
//          various definitions like STB_TEXTEDIT_K_LEFT have the is-key-event bit
//          set, and make STB_TEXTEDIT_KEYTOCHAR check that the is-key-event bit is
//          clear.
//
//   When rendering, you can read the cursor position and selection state from
//   the STB_TexteditState.
//
//
// Notes:
//
// This is designed to be usable in IMGUI, so it allows for the possibility of
// running in an IMGUI that has NOT cached the multi-line layout. For this
// reason, it provides an interface that is compatible with computing the
// layout incrementally--we try to make sure we make as few passes through
// as possible. (For example, to locate the mouse pointer in the text, we
// could define functions that return the X and Y positions of characters
// and binary search Y and then X, but if we're doing dynamic layout this
// will run the layout algorithm many times, so instead we manually search
// forward in one pass. Similar logic applies to e.g. up-arrow and
// down-arrow movement.)
//
// If it's run in a widget that *has* cached the layout, then this is less
// efficient, but it's not horrible on modern computers. But you wouldn't
// want to edit million-line files with it.

////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////
////
////   Header-file mode
////
////

#ifndef INCLUDE_STB_TEXTEDIT_H
#define INCLUDE_STB_TEXTEDIT_H

////////////////////////////////////////////////////////////////////////
//
//     STB_TexteditState
//
// Definition of STB_TexteditState which you should store
// per-textfield; it includes cursor position, selection state,
// and undo state.
//

#ifndef STB_TEXTEDIT_UNDOSTATECOUNT
#define STB_TEXTEDIT_UNDOSTATECOUNT 99
#endif
#ifndef STB_TEXTEDIT_UNDOCHARCOUNT
#define STB_TEXTEDIT_UNDOCHARCOUNT 999
#endif
#ifndef STB_TEXTEDIT_CHARTYPE
#define STB_TEXTEDIT_CHARTYPE int
#endif
#ifndef STB_TEXTEDIT_POSITIONTYPE
#define STB_TEXTEDIT_POSITIONTYPE int
#endif

typedef struct
{
	// private data
	STB_TEXTEDIT_POSITIONTYPE where;
	short insert_length;
	short delete_length;
	short char_storage;
} StbUndoRecord;

typedef struct
{
	// private data
	StbUndoRecord undo_rec[STB_TEXTEDIT_UNDOSTATECOUNT];
	STB_TEXTEDIT_CHARTYPE undo_char[STB_TEXTEDIT_UNDOCHARCOUNT];
	short undo_point, redo_point;
	short undo_char_point, redo_char_point;
} StbUndoState;

typedef struct
{
	/////////////////////
	//
	// public data
	//

	int cursor;
	// position of the text cursor within the string

	int select_start;  // selection start point
	int select_end;
	// selection start and end point in characters; if equal, no selection.
	// note that start may be less than or greater than end (e.g. when
	// dragging the mouse, start is where the initial click was, and you
	// can drag in either direction)

	unsigned char insert_mode;
	// each textfield keeps its own insert mode state. to keep an app-wide
	// insert mode, copy this value in/out of the app state

	/////////////////////
	//
	// private data
	//
	unsigned char cursor_at_end_of_line;  // not implemented yet
	unsigned char initialized;
	unsigned char has_preferred_x;
	unsigned char single_line;
	unsigned char padding1, padding2, padding3;
	float preferred_x;  // this determines where the cursor up/down tries to seek to along x
	StbUndoState undostate;
} STB_TexteditState;

////////////////////////////////////////////////////////////////////////
//
//     StbTexteditRow
//
// Result of layout query, used by stb_textedit to determine where
// the text in each row is.

// result of layout query
typedef struct
{
	float x0, x1;            // starting x location, end x location (allows for align=right, etc)
	float baseline_y_delta;  // position of baseline relative to previous row's baseline
	float ymin, ymax;        // height of row above and below baseline
	int num_chars;
} StbTexteditRow;
#endif  //INCLUDE_STB_TEXTEDIT_H

////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////
////
////   Implementation mode
////
////

// implementation isn't include-guarded, since it might have indirectly
// included just the "header" portion
#ifdef STB_TEXTEDIT_IMPLEMENTATION

#ifndef STB_TEXTEDIT_memmove
#include <string.h>
#define STB_TEXTEDIT_memmove memmove
#endif

/////////////////////////////////////////////////////////////////////////////
//
//      Mouse input handling
//

// traverse the layout to locate the nearest character to a display position
static int stb_text_locate_coord(STB_TEXTEDIT_STRING *str, float x, float y)
{
	StbTexteditRow r;
	int n = STB_TEXTEDIT_STRINGLEN(str);
	float base_y = 0, prev_x;
	int i = 0, k;

	r.x0 = r.x1 = 0;
	r.ymin = r.ymax = 0;
	r.num_chars = 0;

	// search rows to find one that straddles 'y'
	while (i < n)
	{
		STB_TEXTEDIT_LAYOUTROW(&r, str, i);
		if (r.num_chars <= 0)
			return n;

		if (i == 0 && y < base_y + r.ymin)
			return 0;

		if (y < base_y + r.ymax)
			break;

		i += r.num_chars;
		base_y += r.baseline_y_delta;
	}

	// below all text, return 'after' last character
	if (i >= n)
		return n;

	// check if it's before the beginning of the line
	if (x < r.x0)
		return i;

	// check if it's before the end of the line
	if (x < r.x1)
	{
		// search characters in row for one that straddles 'x'
		prev_x = r.x0;
		for (k = 0; k < r.num_chars; ++k)
		{
			float w = STB_TEXTEDIT_GETWIDTH(str, i, k);
			if (x < prev_x + w)
			{
				if (x < prev_x + w / 2)
					return k + i;
				else
					return k + i + 1;
			}
			prev_x += w;
		}
		// shouldn't happen, but if it does, fall through to end-of-line case
	}

	// if the last character is a newline, return that. otherwise return 'after' the last character
	if (STB_TEXTEDIT_GETCHAR(str, i + r.num_chars - 1) == STB_TEXTEDIT_NEWLINE)
		return i + r.num_chars - 1;
	else
		return i + r.num_chars;
}

// API click: on mouse down, move the cursor to the clicked location, and reset the selection
static void stb_textedit_click(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, float x, float y)
{
	state->cursor = stb_text_locate_coord(str, x, y);
	state->select_start = state->cursor;
	state->select_end = state->cursor;
	state->has_preferred_x = 0;
}

// API drag: on mouse drag, move the cursor and selection endpoint to the clicked location
static void stb_textedit_drag(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, float x, float y)
{
	int p = stb_text_locate_coord(str, x, y);
	if (state->select_start == state->select_end)
		state->select_start = state->cursor;
	state->cursor = state->select_end = p;
}

/////////////////////////////////////////////////////////////////////////////
//
//      Keyboard input handling
//

// forward declarations
static void stb_text_undo(STB_TEXTEDIT_STRING *str, STB_TexteditState *state);
static void stb_text_redo(STB_TEXTEDIT_STRING *str, STB_TexteditState *state);
static void stb_text_makeundo_delete(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, int where, int length);
static void stb_text_makeundo_insert(STB_TexteditState *state, int where, int length);
static void stb_text_makeundo_replace(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, int where, int old_length, int new_length);

typedef struct
{
	float x, y;              // position of n'th character
	float height;            // height of line
	int first_char, length;  // first char of row, and length
	int prev_first;          // first char of previous row
} StbFindState;

// find the x/y location of a character, and remember info about the previous row in
// case we get a move-up event (for page up, we'll have to rescan)
static void stb_textedit_find_charpos(StbFindState *find, STB_TEXTEDIT_STRING *str, int n, int single_line)
{
	StbTexteditRow r;
	int prev_start = 0;
	int z = STB_TEXTEDIT_STRINGLEN(str);
	int i = 0, first;

	if (n == z)
	{
		// if it's at the end, then find the last line -- simpler than trying to
		// explicitly handle this case in the regular code
		if (single_line)
		{
			STB_TEXTEDIT_LAYOUTROW(&r, str, 0);
			find->y = 0;
			find->first_char = 0;
			find->length = z;
			find->height = r.ymax - r.ymin;
			find->x = r.x1;
		}
		else
		{
			find->y = 0;
			find->x = 0;
			find->height = 1;
			while (i < z)
			{
				STB_TEXTEDIT_LAYOUTROW(&r, str, i);
				prev_start = i;
				i += r.num_chars;
			}
			find->first_char = i;
			find->length = 0;
			find->prev_first = prev_start;
		}
		return;
	}

	// search rows to find the one that straddles character n
	find->y = 0;

	for (;;)
	{
		STB_TEXTEDIT_LAYOUTROW(&r, str, i);
		if (n < i + r.num_chars)
			break;
		prev_start = i;
		i += r.num_chars;
		find->y += r.baseline_y_delta;
	}

	find->first_char = first = i;
	find->length = r.num_chars;
	find->height = r.ymax - r.ymin;
	find->prev_first = prev_start;

	// now scan to find xpos
	find->x = r.x0;
	i = 0;
	for (i = 0; first + i < n; ++i)
		find->x += STB_TEXTEDIT_GETWIDTH(str, first, i);
}

#define STB_TEXT_HAS_SELECTION(s) ((s)->select_start != (s)->select_end)

// make the selection/cursor state valid if client altered the string
static void stb_textedit_clamp(STB_TEXTEDIT_STRING *str, STB_TexteditState *state)
{
	int n = STB_TEXTEDIT_STRINGLEN(str);
	if (STB_TEXT_HAS_SELECTION(state))
	{
		if (state->select_start > n) state->select_start = n;
		if (state->select_end > n) state->select_end = n;
		// if clamping forced them to be equal, move the cursor to match
		if (state->select_start == state->select_end)
			state->cursor = state->select_start;
	}
	if (state->cursor > n) state->cursor = n;
}

// delete characters while updating undo
static void stb_textedit_delete(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, int where, int len)
{
	stb_text_makeundo_delete(str, state, where, len);
	STB_TEXTEDIT_DELETECHARS(str, where, len);
	state->has_preferred_x = 0;
}

// delete the section
static void stb_textedit_delete_selection(STB_TEXTEDIT_STRING *str, STB_TexteditState *state)
{
	stb_textedit_clamp(str, state);
	if (STB_TEXT_HAS_SELECTION(state))
	{
		if (state->select_start < state->select_end)
		{
			stb_textedit_delete(str, state, state->select_start, state->select_end - state->select_start);
			state->select_end = state->cursor = state->select_start;
		}
		else
		{
			stb_textedit_delete(str, state, state->select_end, state->select_start - state->select_end);
			state->select_start = state->cursor = state->select_end;
		}
		state->has_preferred_x = 0;
	}
}

// canoncialize the selection so start <= end
static void stb_textedit_sortselection(STB_TexteditState *state)
{
	if (state->select_end < state->select_start)
	{
		int temp = state->select_end;
		state->select_end = state->select_start;
		state->select_start = temp;
	}
}

// move cursor to first character of selection
static void stb_textedit_move_to_first(STB_TexteditState *state)
{
	if (STB_TEXT_HAS_SELECTION(state))
	{
		stb_textedit_sortselection(state);
		state->cursor = state->select_start;
		state->select_end = state->select_start;
		state->has_preferred_x = 0;
	}
}

// move cursor to last character of selection
static void stb_textedit_move_to_last(STB_TEXTEDIT_STRING *str, STB_TexteditState *state)
{
	if (STB_TEXT_HAS_SELECTION(state))
	{
		stb_textedit_sortselection(state);
		stb_textedit_clamp(str, state);
		state->cursor = state->select_end;
		state->select_start = state->select_end;
		state->has_preferred_x = 0;
	}
}

#ifdef STB_TEXTEDIT_IS_SPACE
static int is_word_boundary(STB_TEXTEDIT_STRING *str, int idx)
{
	return idx > 0 ? (STB_TEXTEDIT_IS_SPACE(STB_TEXTEDIT_GETCHAR(str, idx - 1)) && !STB_TEXTEDIT_IS_SPACE(STB_TEXTEDIT_GETCHAR(str, idx))) : 1;
}

#ifndef STB_TEXTEDIT_MOVEWORDLEFT
static int stb_textedit_move_to_word_previous(STB_TEXTEDIT_STRING *str, int c)
{
	--c;  // always move at least one character
	while (c >= 0 && !is_word_boundary(str, c))
		--c;

	if (c < 0)
		c = 0;

	return c;
}
#define STB_TEXTEDIT_MOVEWORDLEFT stb_textedit_move_to_word_previous
#endif

#ifndef STB_TEXTEDIT_MOVEWORDRIGHT
static int stb_textedit_move_to_word_next(STB_TEXTEDIT_STRING *str, int c)
{
	const int len = STB_TEXTEDIT_STRINGLEN(str);
	++c;  // always move at least one character
	while (c < len && !is_word_boundary(str, c))
		++c;

	if (c > len)
		c = len;

	return c;
}
#define STB_TEXTEDIT_MOVEWORDRIGHT stb_textedit_move_to_word_next
#endif

#endif

// update selection and cursor to match each other
static void stb_textedit_prep_selection_at_cursor(STB_TexteditState *state)
{
	if (!STB_TEXT_HAS_SELECTION(state))
		state->select_start = state->select_end = state->cursor;
	else
		state->cursor = state->select_end;
}

// API cut: delete selection
static int stb_textedit_cut(STB_TEXTEDIT_STRING *str, STB_TexteditState *state)
{
	if (STB_TEXT_HAS_SELECTION(state))
	{
		stb_textedit_delete_selection(str, state);  // implicity clamps
		state->has_preferred_x = 0;
		return 1;
	}
	return 0;
}

// API paste: replace existing selection with passed-in text
static int stb_textedit_paste(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, STB_TEXTEDIT_CHARTYPE const *ctext, int len)
{
	STB_TEXTEDIT_CHARTYPE *text = (STB_TEXTEDIT_CHARTYPE *)ctext;
	// if there's a selection, the paste should delete it
	stb_textedit_clamp(str, state);
	stb_textedit_delete_selection(str, state);
	// try to insert the characters
	if (STB_TEXTEDIT_INSERTCHARS(str, state->cursor, text, len))
	{
		stb_text_makeundo_insert(state, state->cursor, len);
		state->cursor += len;
		state->has_preferred_x = 0;
		return 1;
	}
	// remove the undo since we didn't actually insert the characters
	if (state->undostate.undo_point)
		--state->undostate.undo_point;
	return 0;
}

// API key: process a keyboard input
static void stb_textedit_key(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, int key)
{
retry:
	switch (key)
	{
		default:
		{
			int c = STB_TEXTEDIT_KEYTOTEXT(key);
			if (c > 0)
			{
				STB_TEXTEDIT_CHARTYPE ch = (STB_TEXTEDIT_CHARTYPE)c;

				// can't add newline in single-line mode
				if (c == '\n' && state->single_line)
					break;

				if (state->insert_mode && !STB_TEXT_HAS_SELECTION(state) && state->cursor < STB_TEXTEDIT_STRINGLEN(str))
				{
					stb_text_makeundo_replace(str, state, state->cursor, 1, 1);
					STB_TEXTEDIT_DELETECHARS(str, state->cursor, 1);
					if (STB_TEXTEDIT_INSERTCHARS(str, state->cursor, &ch, 1))
					{
						++state->cursor;
						state->has_preferred_x = 0;
					}
				}
				else
				{
					stb_textedit_delete_selection(str, state);  // implicity clamps
					if (STB_TEXTEDIT_INSERTCHARS(str, state->cursor, &ch, 1))
					{
						stb_text_makeundo_insert(state, state->cursor, 1);
						++state->cursor;
						state->has_preferred_x = 0;
					}
				}
			}
			break;
		}

#ifdef STB_TEXTEDIT_K_INSERT
		case STB_TEXTEDIT_K_INSERT:
			state->insert_mode = !state->insert_mode;
			break;
#endif

		case STB_TEXTEDIT_K_UNDO:
			stb_text_undo(str, state);
			state->has_preferred_x = 0;
			break;

		case STB_TEXTEDIT_K_REDO:
			stb_text_redo(str, state);
			state->has_preferred_x = 0;
			break;

		case STB_TEXTEDIT_K_LEFT:
			// if currently there's a selection, move cursor to start of selection
			if (STB_TEXT_HAS_SELECTION(state))
				stb_textedit_move_to_first(state);
			else if (state->cursor > 0)
				--state->cursor;
			state->has_preferred_x = 0;
			break;

		case STB_TEXTEDIT_K_RIGHT:
			// if currently there's a selection, move cursor to end of selection
			if (STB_TEXT_HAS_SELECTION(state))
				stb_textedit_move_to_last(str, state);
			else
				++state->cursor;
			stb_textedit_clamp(str, state);
			state->has_preferred_x = 0;
			break;

		case STB_TEXTEDIT_K_LEFT | STB_TEXTEDIT_K_SHIFT:
			stb_textedit_clamp(str, state);
			stb_textedit_prep_selection_at_cursor(state);
			// move selection left
			if (state->select_end > 0)
				--state->select_end;
			state->cursor = state->select_end;
			state->has_preferred_x = 0;
			break;

#ifdef STB_TEXTEDIT_MOVEWORDLEFT
		case STB_TEXTEDIT_K_WORDLEFT:
			if (STB_TEXT_HAS_SELECTION(state))
				stb_textedit_move_to_first(state);
			else
			{
				state->cursor = STB_TEXTEDIT_MOVEWORDLEFT(str, state->cursor);
				stb_textedit_clamp(str, state);
			}
			break;

		case STB_TEXTEDIT_K_WORDLEFT | STB_TEXTEDIT_K_SHIFT:
			if (!STB_TEXT_HAS_SELECTION(state))
				stb_textedit_prep_selection_at_cursor(state);

			state->cursor = STB_TEXTEDIT_MOVEWORDLEFT(str, state->cursor);
			state->select_end = state->cursor;

			stb_textedit_clamp(str, state);
			break;
#endif

#ifdef STB_TEXTEDIT_MOVEWORDRIGHT
		case STB_TEXTEDIT_K_WORDRIGHT:
			if (STB_TEXT_HAS_SELECTION(state))
				stb_textedit_move_to_last(str, state);
			else
			{
				state->cursor = STB_TEXTEDIT_MOVEWORDRIGHT(str, state->cursor);
				stb_textedit_clamp(str, state);
			}
			break;

		case STB_TEXTEDIT_K_WORDRIGHT | STB_TEXTEDIT_K_SHIFT:
			if (!STB_TEXT_HAS_SELECTION(state))
				stb_textedit_prep_selection_at_cursor(state);

			state->cursor = STB_TEXTEDIT_MOVEWORDRIGHT(str, state->cursor);
			state->select_end = state->cursor;

			stb_textedit_clamp(str, state);
			break;
#endif

		case STB_TEXTEDIT_K_RIGHT | STB_TEXTEDIT_K_SHIFT:
			stb_textedit_prep_selection_at_cursor(state);
			// move selection right
			++state->select_end;
			stb_textedit_clamp(str, state);
			state->cursor = state->select_end;
			state->has_preferred_x = 0;
			break;

		case STB_TEXTEDIT_K_DOWN:
		case STB_TEXTEDIT_K_DOWN | STB_TEXTEDIT_K_SHIFT:
		{
			StbFindState find;
			StbTexteditRow row;
			int i, sel = (key & STB_TEXTEDIT_K_SHIFT) != 0;

			if (state->single_line)
			{
				// on windows, up&down in single-line behave like left&right
				key = STB_TEXTEDIT_K_RIGHT | (key & STB_TEXTEDIT_K_SHIFT);
				goto retry;
			}

			if (sel)
				stb_textedit_prep_selection_at_cursor(state);
			else if (STB_TEXT_HAS_SELECTION(state))
				stb_textedit_move_to_last(str, state);

			// compute current position of cursor point
			stb_textedit_clamp(str, state);
			stb_textedit_find_charpos(&find, str, state->cursor, state->single_line);

			// now find character position down a row
			if (find.length)
			{
				float goal_x = state->has_preferred_x ? state->preferred_x : find.x;
				float x;
				int start = find.first_char + find.length;
				state->cursor = start;
				STB_TEXTEDIT_LAYOUTROW(&row, str, state->cursor);
				x = row.x0;
				for (i = 0; i < row.num_chars; ++i)
				{
					float dx = STB_TEXTEDIT_GETWIDTH(str, start, i);
#ifdef STB_TEXTEDIT_GETWIDTH_NEWLINE
					if (dx == STB_TEXTEDIT_GETWIDTH_NEWLINE)
						break;
#endif
					x += dx;
					if (x > goal_x)
						break;
					++state->cursor;
				}
				stb_textedit_clamp(str, state);

				state->has_preferred_x = 1;
				state->preferred_x = goal_x;

				if (sel)
					state->select_end = state->cursor;
			}
			break;
		}

		case STB_TEXTEDIT_K_UP:
		case STB_TEXTEDIT_K_UP | STB_TEXTEDIT_K_SHIFT:
		{
			StbFindState find;
			StbTexteditRow row;
			int i, sel = (key & STB_TEXTEDIT_K_SHIFT) != 0;

			if (state->single_line)
			{
				// on windows, up&down become left&right
				key = STB_TEXTEDIT_K_LEFT | (key & STB_TEXTEDIT_K_SHIFT);
				goto retry;
			}

			if (sel)
				stb_textedit_prep_selection_at_cursor(state);
			else if (STB_TEXT_HAS_SELECTION(state))
				stb_textedit_move_to_first(state);

			// compute current position of cursor point
			stb_textedit_clamp(str, state);
			stb_textedit_find_charpos(&find, str, state->cursor, state->single_line);

			// can only go up if there's a previous row
			if (find.prev_first != find.first_char)
			{
				// now find character position up a row
				float goal_x = state->has_preferred_x ? state->preferred_x : find.x;
				float x;
				state->cursor = find.prev_first;
				STB_TEXTEDIT_LAYOUTROW(&row, str, state->cursor);
				x = row.x0;
				for (i = 0; i < row.num_chars; ++i)
				{
					float dx = STB_TEXTEDIT_GETWIDTH(str, find.prev_first, i);
#ifdef STB_TEXTEDIT_GETWIDTH_NEWLINE
					if (dx == STB_TEXTEDIT_GETWIDTH_NEWLINE)
						break;
#endif
					x += dx;
					if (x > goal_x)
						break;
					++state->cursor;
				}
				stb_textedit_clamp(str, state);

				state->has_preferred_x = 1;
				state->preferred_x = goal_x;

				if (sel)
					state->select_end = state->cursor;
			}
			break;
		}

		case STB_TEXTEDIT_K_DELETE:
		case STB_TEXTEDIT_K_DELETE | STB_TEXTEDIT_K_SHIFT:
			if (STB_TEXT_HAS_SELECTION(state))
				stb_textedit_delete_selection(str, state);
			else
			{
				int n = STB_TEXTEDIT_STRINGLEN(str);
				if (state->cursor < n)
					stb_textedit_delete(str, state, state->cursor, 1);
			}
			state->has_preferred_x = 0;
			break;

		case STB_TEXTEDIT_K_BACKSPACE:
		case STB_TEXTEDIT_K_BACKSPACE | STB_TEXTEDIT_K_SHIFT:
			if (STB_TEXT_HAS_SELECTION(state))
				stb_textedit_delete_selection(str, state);
			else
			{
				stb_textedit_clamp(str, state);
				if (state->cursor > 0)
				{
					stb_textedit_delete(str, state, state->cursor - 1, 1);
					--state->cursor;
				}
			}
			state->has_preferred_x = 0;
			break;

#ifdef STB_TEXTEDIT_K_TEXTSTART2
		case STB_TEXTEDIT_K_TEXTSTART2:
#endif
		case STB_TEXTEDIT_K_TEXTSTART:
			state->cursor = state->select_start = state->select_end = 0;
			state->has_preferred_x = 0;
			break;

#ifdef STB_TEXTEDIT_K_TEXTEND2
		case STB_TEXTEDIT_K_TEXTEND2:
#endif
		case STB_TEXTEDIT_K_TEXTEND:
			state->cursor = STB_TEXTEDIT_STRINGLEN(str);
			state->select_start = state->select_end = 0;
			state->has_preferred_x = 0;
			break;

#ifdef STB_TEXTEDIT_K_TEXTSTART2
		case STB_TEXTEDIT_K_TEXTSTART2 | STB_TEXTEDIT_K_SHIFT:
#endif
		case STB_TEXTEDIT_K_TEXTSTART | STB_TEXTEDIT_K_SHIFT:
			stb_textedit_prep_selection_at_cursor(state);
			state->cursor = state->select_end = 0;
			state->has_preferred_x = 0;
			break;

#ifdef STB_TEXTEDIT_K_TEXTEND2
		case STB_TEXTEDIT_K_TEXTEND2 | STB_TEXTEDIT_K_SHIFT:
#endif
		case STB_TEXTEDIT_K_TEXTEND | STB_TEXTEDIT_K_SHIFT:
			stb_textedit_prep_selection_at_cursor(state);
			state->cursor = state->select_end = STB_TEXTEDIT_STRINGLEN(str);
			state->has_preferred_x = 0;
			break;

#ifdef STB_TEXTEDIT_K_LINESTART2
		case STB_TEXTEDIT_K_LINESTART2:
#endif
		case STB_TEXTEDIT_K_LINESTART:
			stb_textedit_clamp(str, state);
			stb_textedit_move_to_first(state);
			if (state->single_line)
				state->cursor = 0;
			else
				while (state->cursor > 0 && STB_TEXTEDIT_GETCHAR(str, state->cursor - 1) != STB_TEXTEDIT_NEWLINE)
					--state->cursor;
			state->has_preferred_x = 0;
			break;

#ifdef STB_TEXTEDIT_K_LINEEND2
		case STB_TEXTEDIT_K_LINEEND2:
#endif
		case STB_TEXTEDIT_K_LINEEND:
		{
			int n = STB_TEXTEDIT_STRINGLEN(str);
			stb_textedit_clamp(str, state);
			stb_textedit_move_to_first(state);
			if (state->single_line)
				state->cursor = n;
			else
				while (state->cursor < n && STB_TEXTEDIT_GETCHAR(str, state->cursor) != STB_TEXTEDIT_NEWLINE)
					++state->cursor;
			state->has_preferred_x = 0;
			break;
		}

#ifdef STB_TEXTEDIT_K_LINESTART2
		case STB_TEXTEDIT_K_LINESTART2 | STB_TEXTEDIT_K_SHIFT:
#endif
		case STB_TEXTEDIT_K_LINESTART | STB_TEXTEDIT_K_SHIFT:
			stb_textedit_clamp(str, state);
			stb_textedit_prep_selection_at_cursor(state);
			if (state->single_line)
				state->cursor = 0;
			else
				while (state->cursor > 0 && STB_TEXTEDIT_GETCHAR(str, state->cursor - 1) != STB_TEXTEDIT_NEWLINE)
					--state->cursor;
			state->select_end = state->cursor;
			state->has_preferred_x = 0;
			break;

#ifdef STB_TEXTEDIT_K_LINEEND2
		case STB_TEXTEDIT_K_LINEEND2 | STB_TEXTEDIT_K_SHIFT:
#endif
		case STB_TEXTEDIT_K_LINEEND | STB_TEXTEDIT_K_SHIFT:
		{
			int n = STB_TEXTEDIT_STRINGLEN(str);
			stb_textedit_clamp(str, state);
			stb_textedit_prep_selection_at_cursor(state);
			if (state->single_line)
				state->cursor = n;
			else
				while (state->cursor < n && STB_TEXTEDIT_GETCHAR(str, state->cursor) != STB_TEXTEDIT_NEWLINE)
					++state->cursor;
			state->select_end = state->cursor;
			state->has_preferred_x = 0;
			break;
		}

			// @TODO:
			//    STB_TEXTEDIT_K_PGUP      - move cursor up a page
			//    STB_TEXTEDIT_K_PGDOWN    - move cursor down a page
	}
}

/////////////////////////////////////////////////////////////////////////////
//
//      Undo processing
//
// @OPTIMIZE: the undo/redo buffer should be circular

static void stb_textedit_flush_redo(StbUndoState *state)
{
	state->redo_point = STB_TEXTEDIT_UNDOSTATECOUNT;
	state->redo_char_point = STB_TEXTEDIT_UNDOCHARCOUNT;
}

// discard the oldest entry in the undo list
static void stb_textedit_discard_undo(StbUndoState *state)
{
	if (state->undo_point > 0)
	{
		// if the 0th undo state has characters, clean those up
		if (state->undo_rec[0].char_storage >= 0)
		{
			int n = state->undo_rec[0].insert_length, i;
			// delete n characters from all other records
			state->undo_char_point = state->undo_char_point - (short)n;  // vsnet05
			STB_TEXTEDIT_memmove(state->undo_char, state->undo_char + n, (size_t)((size_t)state->undo_char_point * sizeof(STB_TEXTEDIT_CHARTYPE)));
			for (i = 0; i < state->undo_point; ++i)
				if (state->undo_rec[i].char_storage >= 0)
					state->undo_rec[i].char_storage = state->undo_rec[i].char_storage - (short)n;  // vsnet05 // @OPTIMIZE: get rid of char_storage and infer it
		}
		--state->undo_point;
		STB_TEXTEDIT_memmove(state->undo_rec, state->undo_rec + 1, (size_t)((size_t)state->undo_point * sizeof(state->undo_rec[0])));
	}
}

// discard the oldest entry in the redo list--it's bad if this
// ever happens, but because undo & redo have to store the actual
// characters in different cases, the redo character buffer can
// fill up even though the undo buffer didn't
static void stb_textedit_discard_redo(StbUndoState *state)
{
	int k = STB_TEXTEDIT_UNDOSTATECOUNT - 1;

	if (state->redo_point <= k)
	{
		// if the k'th undo state has characters, clean those up
		if (state->undo_rec[k].char_storage >= 0)
		{
			int n = state->undo_rec[k].insert_length, i;
			// delete n characters from all other records
			state->redo_char_point = state->redo_char_point + (short)n;  // vsnet05
			STB_TEXTEDIT_memmove(state->undo_char + state->redo_char_point, state->undo_char + state->redo_char_point - n, (size_t)((size_t)(STB_TEXTEDIT_UNDOCHARCOUNT - state->redo_char_point) * sizeof(STB_TEXTEDIT_CHARTYPE)));
			for (i = state->redo_point; i < k; ++i)
				if (state->undo_rec[i].char_storage >= 0)
					state->undo_rec[i].char_storage = state->undo_rec[i].char_storage + (short)n;  // vsnet05
		}
		STB_TEXTEDIT_memmove(state->undo_rec + state->redo_point, state->undo_rec + state->redo_point - 1, (size_t)((size_t)(STB_TEXTEDIT_UNDOSTATECOUNT - state->redo_point) * sizeof(state->undo_rec[0])));
		++state->redo_point;
	}
}

static StbUndoRecord *stb_text_create_undo_record(StbUndoState *state, int numchars)
{
	// any time we create a new undo record, we discard redo
	stb_textedit_flush_redo(state);

	// if we have no free records, we have to make room, by sliding the
	// existing records down
	if (state->undo_point == STB_TEXTEDIT_UNDOSTATECOUNT)
		stb_textedit_discard_undo(state);

	// if the characters to store won't possibly fit in the buffer, we can't undo
	if (numchars > STB_TEXTEDIT_UNDOCHARCOUNT)
	{
		state->undo_point = 0;
		state->undo_char_point = 0;
		return NULL;
	}

	// if we don't have enough free characters in the buffer, we have to make room
	while (state->undo_char_point + numchars > STB_TEXTEDIT_UNDOCHARCOUNT)
		stb_textedit_discard_undo(state);

	return &state->undo_rec[state->undo_point++];
}

static STB_TEXTEDIT_CHARTYPE *stb_text_createundo(StbUndoState *state, int pos, int insert_len, int delete_len)
{
	StbUndoRecord *r = stb_text_create_undo_record(state, insert_len);
	if (r == NULL)
		return NULL;

	r->where = pos;
	r->insert_length = (short)insert_len;
	r->delete_length = (short)delete_len;

	if (insert_len == 0)
	{
		r->char_storage = -1;
		return NULL;
	}
	else
	{
		r->char_storage = state->undo_char_point;
		state->undo_char_point = state->undo_char_point + (short)insert_len;
		return &state->undo_char[r->char_storage];
	}
}

static void stb_text_undo(STB_TEXTEDIT_STRING *str, STB_TexteditState *state)
{
	StbUndoState *s = &state->undostate;
	StbUndoRecord u, *r;
	if (s->undo_point == 0)
		return;

	// we need to do two things: apply the undo record, and create a redo record
	u = s->undo_rec[s->undo_point - 1];
	r = &s->undo_rec[s->redo_point - 1];
	r->char_storage = -1;

	r->insert_length = u.delete_length;
	r->delete_length = u.insert_length;
	r->where = u.where;

	if (u.delete_length)
	{
		// if the undo record says to delete characters, then the redo record will
		// need to re-insert the characters that get deleted, so we need to store
		// them.

		// there are three cases:
		//    there's enough room to store the characters
		//    characters stored for *redoing* don't leave room for redo
		//    characters stored for *undoing* don't leave room for redo
		// if the last is true, we have to bail

		if (s->undo_char_point + u.delete_length >= STB_TEXTEDIT_UNDOCHARCOUNT)
		{
			// the undo records take up too much character space; there's no space to store the redo characters
			r->insert_length = 0;
		}
		else
		{
			int i;

			// there's definitely room to store the characters eventually
			while (s->undo_char_point + u.delete_length > s->redo_char_point)
			{
				// there's currently not enough room, so discard a redo record
				stb_textedit_discard_redo(s);
				// should never happen:
				if (s->redo_point == STB_TEXTEDIT_UNDOSTATECOUNT)
					return;
			}
			r = &s->undo_rec[s->redo_point - 1];

			r->char_storage = s->redo_char_point - u.delete_length;
			s->redo_char_point = s->redo_char_point - (short)u.delete_length;

			// now save the characters
			for (i = 0; i < u.delete_length; ++i)
				s->undo_char[r->char_storage + i] = STB_TEXTEDIT_GETCHAR(str, u.where + i);
		}

		// now we can carry out the deletion
		STB_TEXTEDIT_DELETECHARS(str, u.where, u.delete_length);
	}

	// check type of recorded action:
	if (u.insert_length)
	{
		// easy case: was a deletion, so we need to insert n characters
		STB_TEXTEDIT_INSERTCHARS(str, u.where, &s->undo_char[u.char_storage], u.insert_length);
		s->undo_char_point -= u.insert_length;
	}

	state->cursor = u.where + u.insert_length;

	s->undo_point--;
	s->redo_point--;
}

static void stb_text_redo(STB_TEXTEDIT_STRING *str, STB_TexteditState *state)
{
	StbUndoState *s = &state->undostate;
	StbUndoRecord *u, r;
	if (s->redo_point == STB_TEXTEDIT_UNDOSTATECOUNT)
		return;

	// we need to do two things: apply the redo record, and create an undo record
	u = &s->undo_rec[s->undo_point];
	r = s->undo_rec[s->redo_point];

	// we KNOW there must be room for the undo record, because the redo record
	// was derived from an undo record

	u->delete_length = r.insert_length;
	u->insert_length = r.delete_length;
	u->where = r.where;
	u->char_storage = -1;

	if (r.delete_length)
	{
		// the redo record requires us to delete characters, so the undo record
		// needs to store the characters

		if (s->undo_char_point + u->insert_length > s->redo_char_point)
		{
			u->insert_length = 0;
			u->delete_length = 0;
		}
		else
		{
			int i;
			u->char_storage = s->undo_char_point;
			s->undo_char_point = s->undo_char_point + u->insert_length;

			// now save the characters
			for (i = 0; i < u->insert_length; ++i)
				s->undo_char[u->char_storage + i] = STB_TEXTEDIT_GETCHAR(str, u->where + i);
		}

		STB_TEXTEDIT_DELETECHARS(str, r.where, r.delete_length);
	}

	if (r.insert_length)
	{
		// easy case: need to insert n characters
		STB_TEXTEDIT_INSERTCHARS(str, r.where, &s->undo_char[r.char_storage], r.insert_length);
		s->redo_char_point += r.insert_length;
	}

	state->cursor = r.where + r.insert_length;

	s->undo_point++;
	s->redo_point++;
}

static void stb_text_makeundo_insert(STB_TexteditState *state, int where, int length)
{
	stb_text_createundo(&state->undostate, where, 0, length);
}

static void stb_text_makeundo_delete(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, int where, int length)
{
	int i;
	STB_TEXTEDIT_CHARTYPE *p = stb_text_createundo(&state->undostate, where, length, 0);
	if (p)
	{
		for (i = 0; i < length; ++i)
			p[i] = STB_TEXTEDIT_GETCHAR(str, where + i);
	}
}

static void stb_text_makeundo_replace(STB_TEXTEDIT_STRING *str, STB_TexteditState *state, int where, int old_length, int new_length)
{
	int i;
	STB_TEXTEDIT_CHARTYPE *p = stb_text_createundo(&state->undostate, where, old_length, new_length);
	if (p)
	{
		for (i = 0; i < old_length; ++i)
			p[i] = STB_TEXTEDIT_GETCHAR(str, where + i);
	}
}

// reset the state to default
static void stb_textedit_clear_state(STB_TexteditState *state, int is_single_line)
{
	state->undostate.undo_point = 0;
	state->undostate.undo_char_point = 0;
	state->undostate.redo_point = STB_TEXTEDIT_UNDOSTATECOUNT;
	state->undostate.redo_char_point = STB_TEXTEDIT_UNDOCHARCOUNT;
	state->select_end = state->select_start = 0;
	state->cursor = 0;
	state->has_preferred_x = 0;
	state->preferred_x = 0;
	state->cursor_at_end_of_line = 0;
	state->initialized = 1;
	state->single_line = (unsigned char)is_single_line;
	state->insert_mode = 0;
}

// API initialize
static void stb_textedit_initialize_state(STB_TexteditState *state, int is_single_line)
{
	stb_textedit_clear_state(state, is_single_line);
}
#endif  //STB_TEXTEDIT_IMPLEMENTATION