6.831 User Interface Design & Implementation
Fall 2004
PS4: Rotatable Labels
Due 5 pm, Friday, October 15, 2004, by email
This assignment explores the following topics:
delegation to other components (JLabel);
bounding box computation;
using coordinate transformations in drawing (rotation);
direct-manipulation rotation.
In this problem set, you will implement a variant of JLabel that can
display text rotated at an arbitrary angle. You will also
implement a
controller that allows the user to rotate a label with the mouse.
This problem set lays the groundwork for PS5, in which you will create
automatic layout managers that adjust not only size and position but
also rotation angle.
The RLabel implementation we gave you ignores its angle property,
instead
always displaying the label with no rotation. Complete this class
so that it draws itself at the appropriate angle.
RLabel should compute the correct bounding box for its own
layout. It should draw the label centered in the bounding box,
rotated by the given angle around that center. The comments in
RLabel explain how the angle should be interpreted. RLabel's get
and set methods should behave correctly, including updating the label
appropriately when the text or angle are changed by setText() or
setAngle().
You may find the Math
class useful for trigonometric functions, Graphics2D
essential for drawing with rotation and translation, and AffineTransform
useful for reproducing the coordinate transformations done by
Graphics2D.
RLabel has a main method for testing. Once you have finished
making your changes, this main method should produce the following
window:
Note that the text is surrounded by an orange rectangle. We did
this just for debugging, so that it's easy to check that your RLabel is
producing the correct bounding box. When the test window first
appears, it should fit tightly around the RLabel (give or take a pixel
or two, because of roundoff error).
RLabel.main() takes the angle of the label as an optional
command-line argument (but be warned that this angle is measured
in degrees, not radians). Test your RLabel at different angles to
ensure that you're computing the correct
bounding box and painting correctly.
Problem 2: RotateInteractor (30%)
Design and implement a RotateInteractor that can freely rotate
RLabels. Your RotateInteractor should be able to listen to any
number of RLabels, but since the user has only one mouse,
RotateInteractor only needs to actively turn one label at a time.
When the mouse is pressed and dragged on an
RLabel (anywhere in its bounding box, not just on the orange
rectangle), RotateInteractor should rotate it, following the mouse,
until
the mouse button is released. To determine how far the label
should be turned, compute the angle between two lines: one from the
center of the label to the point where the mouse was pressed, and the
other from the center to the mouse's current position. You'll find Math.atan2()
helpful for computing this angle.
Change RLabel's main method so that the test window uses a
RotateInteractor to allow the label to be rotated freely. (Note:
don't try to resize the window automatically to keep the RLabel tightly
packed in it while it's being rotated. The intial window size
should be tightly packed, but from then on, let the user control the
window size.)
Questions (30%)
Answer the following questions in readme.txt.
In the code you've written, the JLabel is used merely as a
delegate for painting -- i.e., as a stencil. Suppose instead that
the JLabel is added as a child
component of the RLabel. What would the RLabel have to do
to ensure that the JLabel is correctly painted at the correct
rotation? Think about both the initial paint and subsequent
repaints.
Suppose we wanted to build an RScrollBar that could display a
working JScrollBar at any angle of rotation. What would the
RScrollBar have to do to make sure that the scrollbar's input handling
worked properly?
Rotate your RLabel very slowly, a pixel at a time, and observe
that the text doesn't turn smoothly. What happens? What
does this tell you
about how Swing draws text?
What to Hand In
Package your completed assignment as a jar file, as described in PS0. Here's a checklist of things you
should
confirm before you hand in:
all your Java
source is included in your jar file (Javadoc documentation isn't
necessary)
the main class
of your jar file is RLabel
all necessary third-party libraries are
included,
either inside your jar or as separate jars referenced by your jar's
classpath
any resources used by your code are included
in the jar and referenced as resources
readme.txt is included, and it
answers the questions above and credits anybody you discussed the
assignment with
Before you submit your solution, put all the jar files you plan to
submit in an empty directory and make sure you can run it:
java
-jar yourfile.jar
Submit your solution by email
(with
all required jar files attached) to rcm+handin@graphics.csail.mit.edu
no later than 5:00 pm next Friday.
