Comments on: Exercise 5-9: Bouncing Ball

By: william

william — Sat, 04 Feb 2012 17:20:00 +0000

This sounds like two separate questions:
1. How do I constrain the ball in a smaller square area?
– Off the top, measure the radius of the ball and subtract that from the maximum x & y value; add the radius value on any zero value for x and y.
2. How do I constrain the ball to a circle area?
– See shiffman’s polar coordinates for constraining to a circle

By: Anonymous

Anonymous — Mon, 12 Dec 2011 02:10:00 +0000

Check out the concept of Polar coordinates.

http://www.learningprocessing.com/examples/chapter-13/example-13-5-polar-to-cartesian/

By: Fame_frame

Fame_frame — Fri, 09 Dec 2011 12:44:00 +0000

i have also tried constraining the ball in a smaller square area of the screen so that the whole ball is visible at all times but I am having a nightmare time trying to restrict its movement within a circle…any ideas?

By: Readydot WeAre

Readydot WeAre — Sat, 17 Sep 2011 07:32:00 +0000

The constrain is just a measure to keep sure the ball is kept between the two states of the variable “r”, which are 32 and 64. The -2 adds a little animation to the shrinking of the ball, so it does not just change from 64 to 32, but after being 64, “-2″ are subtracted a each redraw until it reaches 32. Replace the 2 by a 1 and the effect is far more obvious.

By: Mi Dan

Mi Dan — Fri, 02 Sep 2011 12:43:00 +0000

What does “r-2″ exactly do in the constrain function, in the last line?
I’ve searched Processing’s help but it wasn’t explained there either…

By: Daniel Shiffman

Daniel Shiffman — Thu, 04 Feb 2010 01:52:10 +0000

It would probably be easier to understand if I wrote the code like this:

r = r - 2;
r = constrain(r,32,64);

In other words, we want r to always get smaller, but never go below 32 (or above 64). The constrain function allows you to perform a mathematical operation at the same time and decrease the value or r, while constraining it.

r = constrain(r-2,32,64);

By: P3HO

P3HO — Wed, 03 Feb 2010 08:51:22 +0000

r = constrain(r-2,32,64);

I can’t unterstand why the first value of constrain() is not “r” but “r-2″.
I changed the value “r-2″ to “r”, then the ball size went up to 64 when it touch the screen and didn’t come back to 32.
Please explain me.. the roll of constrain() in this example!