Function stb_text_undo

KBotExt/imgui/imstb_textedit.h:1210–1277

}

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) {
				// should never happen:
				if (s->redo_point == STB_TEXTEDIT_UNDOSTATECOUNT)
					return;
				// there's currently not enough room, so discard a redo record
				stb_textedit_discard_redo(s);
			}
			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 - 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) {