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The Canvas is the only widget that has both click and release events, and the Button is the only widget that responds to keyboard presses, so you can’t make something that starts when you hold a key and stops when you release.

However, you can make the button send a click, then wait a while, then send a release, which is probably as close as you’re going to get:

on click do
 canvas1.event["click" 0,0]
 sleep[15] # in 60ths of a second
 canvas1.event["release" 0,0]
end

That can look a little weird, since Decker disables all interactive widgets (drawing them greyed out) until the sleep time is complete, but it prevents the player from doing more things while the previous things are still going on.

If you don’t want to freeze things like that, you can build something a little more complex that lets Decker keep doing things while you wait. Create a field to hold the timer countdown, and change the button click handler to:

on click do
 canvas1.event["click"]
 field1.data:15
 field1.animated:1
end

So when the button is clicked, it sends the click event to the Canvas, it loads 15 into the field, and sets the field to be animated (so Decker sends it view events 60 times a second). The field’s view handler looks like this:

on view do
 me.data:me.data - 1
 if me.data = 0
  canvas1.event["release" 0,0]
  me.animated:0
 end
end

So every time view is called (that is, 60 times a second), it subtracts 1 from the value it stores. When it reaches 0, it sends the release event to the canvas, and turns off animation again. As a result, when the button is clicked, the canvas is “clicked”, then things keep happening as usual while the timer ticks down, and when it does the canvas is “released”.

The field can be made “Show None” if you don’t want the player to see it; if you make the button “Show None” then it won’t react to the keyboard. However, you can make the button use the “Invisible” style to hide it, and “Show Transparent” to make it invisible even when clicked. You can also just move it off-screen.