How to execute Re-drawing ?

I analyze a source file of mozilla and convert for my purpose.

I draw the character and the line in the form which overwrites a display portion of mozilla.

I want to execute re-drawing in nsWindow.cpp( widget/src/gtk/ ).

For example re-drawing is executed by mouse middle click.

But I don't know how to execute re-drawing.

Please teach me how to execute re-drawing.