Exercise 1: Getting Your Hands Dirty

Exercise 1 should be a fun, fairly easy undertaking.  Its intention is
to get you into the frame of mind of interactive geometric computation.
It is due in one week (actually, eight days), on Tuesday 17 February.
We'll show off the more interesting resulting executables in class.

The first thing you should do is read through the brief overview
of "gvis," a framework we built with help from Eric Amram.  Then,
compile, run, and look through the code.  It has a reasonably generic
structure allowing extensible geometric primitives (object.[CH]) and 3D
interaction techniques (app.[CH], especially the UserUpdate() method).

Start with something simple and easy.  Use fdesign to add a control
of your choice to the UI.  For example, add a button or a choice to
control some aspect of the display.  Add a slider to change a parameter
of the physical simulation.  Tell fdesign which callback it should
generate when the control you've added is manipulated, then add a
wrapper for this callback to ui.C.  Now modify your program (by editing
app.[CH] or object.[CH] or both) to incorporate the new control.  This
should take about an hour.

Now move onto something more interesting, and more challenging.
Define and implement a new kind of GeomObject.  It doesn't have to
be complicated -- for example, you could make a rectangle that can
have an arbitrary normal.  Or a cylinder or cube or tetrahedron.  If
you're feeling adventurous, you could define a surface z = f(x,y) and
constrain existing or new objects to it as you drag them around and/or
let them time evolve under some simulation.  This should take about
two hours.

Finally, do something interesting with  the UserEvolve() method.
Perhaps you can define a potential field and constrain your objects
to orbit under its influence.  Or, you could make the user-selected
object an attractor or repellor of the other objects.  Or you could do
something altogether different.  Be creative.  This should take just
another few hours.  For extra credit (and to get your executable
shown off in class), do something really interesting, or something
useful to the class -- for example, add some useful viewing or
selection capability, or geometric primitive, to gvis.

The point of this exercise is not to get a high grade.  Again, it's to
introduce you to a new model of interactive, reactive -- even
proactive -- programming.  Enjoy !

Download instructions for athena:

6.838 exercise 1 is now available from the course locker.

to get it, do at the athena prompt

    attach 6.838

    cp -r /mit/6.838/S98/packages/EX1 .

    cd EX1

    make

    cd gvis

    ./gvis

next, add to your executable path the directory

    /mit/6.838/S98/packages/XForms/DESIGN

(if you do this and don't log out and back in, or start

a new shell, you'll have to type "rehash" afterward.)

now you can use XForms' gui builder to add UI components:

    fdesign gvis_xforms.fd

finally, to add functionality you should need only to

edit files in the gvis/ directory.  we have also included

gprims/ (for basic point/vector/plane classes) and

glforms/ (for the opengl canvas and manipulation) in the

distribution in case you wish to modify those.

enjoy !

Last modified: Feb 1998