XmTextGetTopCharacter man page
XmTextGetTopCharacter — A Text function that accesses the position of the first character displayed
#include <Xm/Text.h> XmTextPosition XmTextGetTopCharacter( Widget widget);
XmTextGetTopCharacter accesses the position of the text at the top of the Text widget. If there is no text in the Text widget (in other words, XmNvalue contains an empty string), then XmTextGetTopCharacter returns 0.
Suppose that the XmNtopCharacter resource has been set to a value greater than the number of characters in the text widget. In this case, XmTextGetTopCharacter returns an XmTextPosition value identifying the position of the first character in the last line of text in a multiline case; otherwise, it identifies the position of the last character in the line.
Specifies the Text widget ID
For a complete definition of Text and its associated resources, see XmText(3).
Returns an XmTextPosition value that indicates the state of the XmNtopCharacter resource. This is an integer number of characters from the beginning of the text buffer. The first character position is 0 (zero).