Detecting a mouse click / mouse up in NetLogo - user-interface

Question

Using mouse-down? for mouse actions in NetLogo often results in the action happening too many times. For example, if you want to let users click to create new turtles, you could hook a forever button up to a procedure like:
to add-turtle
if mouse-down? [
crt 1 [ setxy mouse-xcor mouse-ycor ]
]
end
The problem is that this usually results in many turtles being created per click. I'd like to do something like:
to add-turtle
if mouse-clicked? [
crt 1 [ setxy mouse-xcor mouse-ycor ]
]
end
Where mouse-clicked? is true right as the person clicks (right after they left up the mouse button).

Answer 1

Unfortunately, you do have to keep track of it yourself, but the good news is that its not hard.
The key is to create a global called mouse-was-down? that is set to true if mouse-down? was true in the last time your mouse-oriented procedure was called. Then mouse-clicked? can be defined as follows:
to-report mouse-clicked?
report (mouse-was-down? = true and not mouse-down?)
end
It seems to work well in conjunction with a central mouse-management procedure that calls the other click-based procedures. For example:
globals [ mouse-was-down? ]
to-report mouse-clicked?
report (mouse-was-down? = true and not mouse-down?)
end
to mouse-manager
let mouse-is-down? mouse-down?
if mouse-clicked? [
add-turtle
; Other procedures that should be run on mouse-click
]
set mouse-was-down? mouse-is-down?
end
to add-turtle
crt 1 [ setxy mouse-xcor mouse-ycor ]
end
Using the mouse-is-down? local variable keeps the behavior more consistent if the mouse button is released before mouse-manager finishes.

Answer 2

Hello probably this is a bit late for your purpose, but in case anyone has the same problem, this is how I solved this in my models for now.
to add-turtle
if mouse-down? [
crt 1 [ setxy mouse-xcor mouse-ycor ]
stop
]
end
The workaround here is to add a "stop" command to kill the "create-new-turtle" forever button. The only tradeoff is that you will have to press again to create another new turtle.

Answer 3

Bryan Head's answer didn't work for me, it still created multiple turtles in one click.
Alternative:
A (non-forever) button which does crt 1 [ setxy mouse-xcor mouse-ycor ] with action key A.
Now all you need to do to add a turtle is press or hold A with your left hand while mousing with your right hand.

Answer 4

Here is an alternative to Bryan's code, in case you want to perform an action as soon as the mouse button is clicked (instead of waiting until it's released):
globals [ mouse-clicked? ]
to mouse-manager
ifelse mouse-down? [
if not mouse-clicked? [
set mouse-clicked? true
crt 1 [ setxy mouse-xcor mouse-ycor ]
]
] [
set mouse-clicked? false
]
end