'''This is a request for comments on this patch. I'd appreciate a review of this code; if any issues are found, I'll gladly fix them and submit a new revision below.'''


Before now, in a text entry box, editing could only occur at the end of the text string. With this patch, one can move the cursor around inside of text entry boxes using the keyboard. Now the middle of a text string can be edited, as well. Left/right arrows, backspace, delete, home, and end keys work as expected.


'''Concerns/Possible improvements''':
* Where to put the cursorPosition variable -- into an existing struct, or global? It seemed to fit well next to the global isAborted variable.
* Because the UTF-8 editing functions ''UTF8_insert_char()'' and ''UTF8_delete_char()'' work with byte offsets instead of UTF-8 character offsets, I had to create a new function, "UTF8_char_offset_to_byte_offset" to convert from one to the other.
* Would it make more sense for the UTF-8 functions to be edited to use UTF-8 character offsets instead of byte offsets? ''UTF8_insert_char()'' and ''UTF8_delete_char()'' are ONLY used for text entry boxes, so can be changed quickly and easily.
* Possible future improvement: when text is larger than the text entry box, always scroll to the text at the cursor.
* Possible future improvement: cursor can disappear when text uses about 62 bytes. Due to preexisting off-by-one bug in UTF8_insert_char(), fortunately in the overly-cautious direction.
* Possible future improvement: text only displays about the first 62 bytes before cutting off. Due to preexisting mismatch between cvar size and buffer size for display.
* Possible future improvement: graphical cursor instead of a text character cursor.
* Possible future improvement: add ability to select cursor position using mouse.


(Additional keywords for future searches: textboxes, text editing boxes, "edition".)