Hint 1:
Use noFill() before rectangle.
Hint 2:
mx is declared twice! Only declare it globally once or locally in draw() for immediate use.
You do not use mx in code.
Use mx to constrain location of ellipse.
Hint 3:
Look at range of your constrain() for mouseX; you have a Y location in there as a limit.
Hint 4:
void mousePressed() has multiple mousePressed inside it; this function executes if mouse is pressed so you do not have to keep checking it.
Work on above first and look at example I posted before.
Going for a long hike in woods and not back for a while.
