on.grabDown

The event on.grabDown is used to handle grabbing motions (cursor press & hold).

This routine is called in these situations:

• When the user presses and holds the Select key on a device
• When the user presses Ctrl + Select on a device
• When the user presses the middle mouse button over an active card on the desktop

The passed coordinated, x and y, are always 0 and 0. The grabDown and grabUp events prevent the generation of a mouseUp event in all cases.

They will be preceded by a on.mouseDown event when generated by pressing and holding the Select key on a device.

Example

Below is an example of a program that handles the grabbing motion to move an object :

function Ball:move(x,y)
     self.x = x
     self.y = y
     platform.window:invalidate()
end

function on.grabDown(x,y)
     isGrabbing = not isGrabbing -- makes the variable switch from true to false and vice versa
     platform.window:invalidate()
end

function on.mouseMove(x,y)
     if isGrabbing and (trackedBall and trackedBall.isActive) then  -- assuming trackedBall is defined etc. 
         trackedBall:move(x-trackedBall.r/2,y-trackedBall.r/2)
     end
end

You can see the whole lua example about Ball generation and movements here : Balls Example (Class + Events Handling)

See Also

on.grabUp