9. Low-Level UI in Squeak

• Down and Dirty UI in Squeak
• You can draw to the Display to make anything appear.
• 'abc' displayAt: 0@0
• You can access Sensor to find out what the user's events are.
• What Sensors Understand
• Sensor is a global variable holding an instance of class InputSensor
• Keyboard Manipulation
• keyboardPressed, keyboardPeek, keyboard, flushKeyboard
• Mouse Manipulation
• waitButton, waitNoButton, waitClickButton
• redButtonPressed, blueButtonPressed, yellowButtonPressed, anyButtonPressed, noButtonPressed
• mousePoint, cursorPoint
• Tour of the Drawing Editor
• Object subclass: #DrawingEditor
• instanceVariableNames: 'drawObjects state background '
• classVariableNames: ''
• poolDictionaries: ''
• category: 'Object-Drawing'
• Starting the Drawing Editor
• DrawingEditor methodsFor: 'all' stamp: 'mjg 12/13/97 21:50'
• initialize
• "Define a white background, but can really draw anywhere."
• background := (Form extent: 400@400) fillWhite.
• background display.
• drawObjects := OrderedCollection new. "List of all objects"
• self processEvents.
• Event Handling in Drawing Editor
• processEvents
• "If right (blue) button pressed, stop the editor. Otherwise, wait for a left (red) button. If it's in an object, drag the object along then redraw all objects. If it's not, draw a new object."
• | startLoc target |
• [Sensor blueButtonPressed] whileFalse:
• [(Sensor redButtonPressed)
• ifTrue: [startLoc := Sensor mousePoint. "This gives us the cursor point"
• target := self objectAt: startLoc.
• target isNil ifTrue: [self drawObject: startLoc]
• ifFalse: [self trackObject: target. self redrawObjects.]]]
• Drawing a New Object and Rubber-Banding
• drawObject: startLoc
• "Handles the rubber-banding of drawing a new rectangle, then adds it to the list of objects, then redraws everything (slow but effective)."
• | newObject |
• Sensor waitNoButton. "Wait until the starting mouseclick is done"
• newObject := Rectangle origin: startLoc extent: 10@10. "Start with a little rect"
• [Sensor redButtonPressed] whileFalse: "Wait for the next click"
• [newObject display: (Color white). "Draw it the background color, to erase it"
• newObject := (Rectangle origin: startLoc corner: (Sensor mousePoint)). "Define a new rectangle"
• newObject display: (Color gray). "Display it gray, for rubberbanding" ].
• drawObjects add: newObject. "Add it to our display list"
• self redrawObjects. "Ask the background and each object to draw itself."
• Redrawing Everything
• redrawObjects
• "Redraw our white background Form, then refresh each object."
• background display.
• drawObjects do: [:anObject | self refreshObject: anObject].
• refreshObject: object
• "Create a form the same size as the object, make it red, then draw it on the display"
• | f |
• f := Form extent: (object extent) depth: (Display depth).
• f fillColor: (Color red).
• f displayOn: Display at: object origin.
• Finding Objects
• Who got clicked on?
• objectAt: startLoc
• "Checks all of the objects to determine which one contains the mouse point"
• ^(drawObjects detect: [:r | r containsPoint: startLoc] ifNone: [nil])! !
• Tracking a Moving Object
• trackObject: dobject
• "Lets the user drag around a track of the object, then drops the new object"
• | offset extent newObject |
• offset := dobject origin - Sensor mousePoint. "Where in me is the mouse pointer?"
• extent := dobject extent. "We'll need this, so that the rect keeps its size"
• newObject := dobject. "newObject is what we'll manipulate later"
• drawObjects remove: dobject. "Take the old one off the redraw list"
• [Sensor redButtonPressed] whileTrue: "Wait until dropped"
• [newObject display: (Color white). "Clear the old one, then define a new one"
• newObject := Rectangle origin: (Sensor mousePoint) + offset extent: extent.
• newObject display: (Color red). "Trace the new one"].
• newObject display: (Color white). "Delete the last trace"
• drawObjects add: newObject. "Then add the new rect to the objects list"