A button morph with separate images for on, off, and pressed with the mouse.

When the event actWhen occurs, send actionSelector with 'arguments' to target. For other events, default to my eventHandler. The current event is not supplied in the arguments to the actionSelector.

image (a.k.a. onImage) may not be nil. offImage and pressedImage may be nil. nil there means be transparent and show the underlying object.

Tools for debugging:
Display the images momentarily under program control (for positioning) (self is an instance).
self state: #on. self state: #off.
self state: #pressed. self state: #off.
Display a rectangle where the button is.
Display fillWithColor: bounds + (self world viewBox origin).
self invalidRect: bounds.

	copying
	updateReferencesUsing: veryDeepFixupWith: veryDeepInner:

	drawing
	drawOn:

	event handling
	doButtonAction doButtonAction: handlesMouseDown: handlesMouseStillDown: mouseDown: mouseMove: mouseStillDown: mouseUp:

	geometry
	extent extent:

	initialize-release
	adaptToWorld: initialize

	printing
	printOn:

	stepping
	step stepTime wantsSteps

	testing
	isOn

	instance creation
	checkBox radioButton

	accessing	top
	actWhen: Accepts symbols: #buttonDown, #buttonUp, and #whilePressed
	actionSelector
	actionSelector:
	arguments
	arguments:
	authorModeOwner:
	dragIfAuthoring: Allow simple dragging if the class var is set to my owner.
	offImage
	offImage:
	onImage
	onImage:
	pressedImage
	pressedImage:
	state: Change the image and invalidate the rect.
	target
	target:

	copying	top
	updateReferencesUsing: If the arguments array points at a morph we are copying, then update it to point to the new copy. This method also copies the arguments array itself, which is important!
	veryDeepFixupWith: If target and arguments fields were weakly copied, fix them here. If they were in the tree being copied, fix them up, otherwise point to the originals!!
	veryDeepInner: Copy all of my instance variables. Some need to be not copied at all, but shared. Warning!! Every instance variable defined in this class must be handled. We must also implement veryDeepFixupWith:. See DeepCopier class comment.

	drawing	top
	drawOn:

	event handling	top
	doButtonAction Perform the action of this button. Subclasses may override this method. The default behavior is to send the button's actionSelector to its target object with its arguments.
	doButtonAction: Perform the action of this button. Subclasses may override this method. The default behavior is to send the button's actionSelector to its target object with its arguments.
	handlesMouseDown: Do I want to receive mouseDown events (mouseDown:, mouseMove:, mouseUp:)?
	handlesMouseStillDown: Return true if the receiver wants to get repeated #mouseStillDown: messages between #mouseDown: and #mouseUp
	mouseDown: Handle a mouse down event. The default response is to let my eventHandler, if any, handle it.
	mouseMove: Handle a mouse move event. The default response is to let my eventHandler, if any, handle it.
	mouseStillDown: Handle a mouse move event. The default response is to let my eventHandler, if any, handle it.
	mouseUp: Allow on:send:to: to set the response to events other than actWhen

	geometry	top
	extent Do it normally
	extent: Do it normally

	initialize-release	top
	adaptToWorld: The receiver finds itself operating in a possibly-different new world. If any of the receiver's parts are world-dependent (such as a target of a SimpleButtonMorph, etc.), then have them adapt accordingly
	initialize

	printing	top
	printOn: Append to the argument, aStream, a sequence of characters that identifies the receiver.

	stepping	top
	step Do some periodic activity. Use startStepping/stopStepping to start and stop getting sent this message. The time between steps is specified by this morph's answer to the stepTime message. The generic version dispatches control to the player, if any. The nasty circumlocation about owner's transformation is necessitated by the flexing problem that the player remains in the properties dictionary both of the flex and the real morph. In the current architecture, only the top renderer's pointer to the player should actually be honored for the purpose of firing.
	stepTime Answer the desired time between steps in milliseconds. This default implementation requests that the 'step' method be called once every second.
	wantsSteps Return true if the receiver overrides the default Morph step method.

	testing	top
	isOn

	class initialization	top
	initialize ThreePhaseButtonMorph initialize

	instance creation	top
	checkBox Answer a button pre-initialized with checkbox images.
	radioButton Answer a button pre-initialized with radiobutton images.