Unity 2D C# - no collision inside an object

Question

I want to know, how to get no collision inside an object. I have a big circle and inside the circle is a smaller square. When the game starts, the circle is scaling down. And what i want, is to check the collision, if circle is touching or is inside the square.

Can you please help me ? Thank you

Do both the circle and the square have the same center? Because if so, you could use basic maths and wouldn't need any collision detection at all. — Keiwan, Dec 23 '16 at 18:43
Yeah, they have same center. And other thing, that i want to mention is about changing sprite of the gameobject. The circle can be changed on the triangle or square and other geometric things — CallMany, Dec 23 '16 at 18:48
But it will be ok, if you tell me how to detect the collision of these two object ( square - circle) — CallMany, Dec 23 '16 at 19:08

Keiwan · Answer 1 · 2016-12-23T21:11:10.133

1

As far as I know there is no built-in way of achieving this in Unity (There is also not a built-in way of detecting whether a collider is fully inside another collider or not).

If I understood you correctly your circle is going to shrink and when it reaches this point

you want to do something e.g. execute some code.

The way you could make it work for a circle and a square just based on maths would be this:

If the sides of your square are of length a and your circle has a decreasing radius of r, then at the moment you see in the image above the relation between the two of them is:

r = a / sqrt(2)

So you could check if (r <= a / Mathf.Sqrt(2)) in the Update function and based on that call some function. (Maybe add another boolean to ensure the function only gets called once.)

You can get your sprite widths using

width = GetComponent<SpriteRenderer>().bounds.size.x;

The radius of your circle would then obviously be half the width of the circle sprite.

You should probably also store the SpriteRenderer in a variable once instead of calling GetComponent on every frame.

For an equilateral triangle the equation would be

r = a / sqrt(3)

where a is the length of the triangle's side.

edited Dec 23 '16 at 21:11

answered Dec 23 '16 at 20:11

Keiwan

8,031
5
36
49

Oh, thank you so much. And what about that triangle ? If triangle will be there instead square ( Big circle - smaller triangle) – CallMany Dec 23 '16 at 20:54
Well, that would depend on the specific triange shape. Is it an equilateral triangle? – Keiwan Dec 23 '16 at 20:58
Yes, that triangle – CallMany Dec 23 '16 at 21:09
@CallMany I added that to the answer as well. – Keiwan Dec 23 '16 at 21:11
@CallMany Are you sure that you divided your circle sprite width by two to get the radius? If you don't you'll simply be calculating using the diameter instead of the radius which works as long as you multiply by `sqrt(2)` instead of divide. – Keiwan Dec 23 '16 at 22:55
Yes, that's it... Thanks – CallMany Dec 24 '16 at 09:17

Unity 2D C# - no collision inside an object

1 Answers1