Unit tests and Line vs Circle | Coding a 2D Physics Engine in Java #6

In this episode I go over how to tell if a line segment is intersecting with a circle. We use some fancy math to project the vector from the line's beginning to the center of the circle onto the line segment, then we check the length of that against the length of the line. If the length of the circle to beginning of the line segment is less than the lenght of the line segment and greater than zero, then the line is intersecting. I also go over how to create unit tests for all these functions. So, we integrate JUnit, then set up a simple test class, and finally add the test class to our build configuration so that unit tests are run before the program is started every time. This is a good way to ensure that your code doesn't break if you change things in the future.

0:00 Intro
0:44 Math behind line vs circle
6:11 Coding line vs circle
10:51 Setting up unit tests

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My Recommended Beginning Game Programming Books:

My Recommended Java Books:

[prashanthkumar]

well there's a small error

A.B=|A| |B| cos (ø)
and B.B = |B|² cos(0) not cos(ø)
so u cant cancel it at 4:35

[Sculman]

You got some pretty high quality tutorials. I really hope this channel will gain more traction. Keep it up!

[NatHsu]

I think your point on line test will miss another edge case where the line is very close to vertical but not quite, say something like (0, 0) to (min_float, 1000). In your point on line function it would probably be better to check if m is infinity and then handle that case instead of checking if dx is 0

[SyloRiyami]

Great video! I just want to point out that (A · B)/(B · B) is ||A|| Cosθ(between A and B)/||B|| Cosθ(between B and B which is 1). :)

[chingoputoh]

I got stuck at this part because my project has neither a test folder nor Gradle.. I'm using a much more recent version of intellij and didn't create my project as a gradle project so could that be the reason?

[alanvandenbosch]

Hi ! and thank you for this serie ! I have a question: In the lineAndCircle() method, you wrote "ab = Isn't it equal to "Vector2f(line.getStart())" ?? I'm trying to do that in javascript and I created a class "Line2D" that takes two vectors for start and end arguments. (I hope my english is not too bad :p). Thanks again !
Edit: It's not, I think i understood.

[carljeffersondelfin]

what exactly is dot method in vector? sorry I'm confused