Java Direct Manipulation Chris North cs3724: HCI

Java Review Java Swing components, Layout managers Events Graphics JDBC, MVC

Hit Testing Mouse click, mouse over Which dot did user click on? Using components: Make each dot a simple component, like a JButton Hit testing automatic, each component is a subwindow Listen to each component Receive event, check event source rectangular items, scalability, customize JComponent Using custom graphics: Get click event x,y from JPanel Iterate through data structure, test for hit Or, shape.contains(x,y) Data structure for fast lookup?

Manipulation Dragging, stretching, … MouseDrag, MouseMove events Using components: mousePressed store x,y click in component mouseDragged –Calculate delta –Move component by delta Using graphics: (need to erase it, repaint other graphics, repaint new item) Calculate delta, calculate new item location, store Call repaint( ) Draw new graphics in paintComponent( )

Problem Dynamic manipulation on top of other graphics Need to preserve (redraw) other graphics Examples: MacDraw, powerpoint Simple solution: Call repaint( ) while dragging paintComponent( ) restores other graphics But: lots of graphics, too slow!

Solutions Minimize repaint rectangle: mypanel.repaint(rect) where rect is area of manipulation paintComponent( ) process only graphics in rect Modified double buffering: maintain buffer for background graphics Paint buffer to screen, then paint manip graphics XOR painting: Draw manipulations by inverting pixel colors drawing with XOR twice returns to original look graphics.setXORMode(color) graphics.setPaintMode( ) for normal painting

In JBuilder

Drag-n-Drop Drag and Drop API Data transfer

Problem: Flashing Ugly flashing when repaint: Paint background Redraw shapes

Solution: Double buffering

Double buffered repaint: Draw all graphics in temporary off-screen image »Paint background color »Paint shapes Then paint image to JPanel Bonus: Swing does this for you! Draw graphics on JPanel JPanel maintains off-screen image