How to raycast via a touch screen to hit very small objects?

Unity Engine
1

Hey all,

I got a problem. May be some of you have an idea or work around for this anoying issue.

My setup: I have a space game on an android platform. The player selects objects on screen via touch (with his or her big fingers :wink: ). In case my objects are far away from the player (so objects are quiet small) it is really difficult to hit this objects with a raycast. The player has to try several times to get it.

I found SphereCast having a ray with a diameter, but it does not work with the option "isTrigger " so I can not use it.

Another idea was fireing a grid of raycasts but I am not sure if this is bad for ths system performance because of the calculations for every single ray.

Any ideas?
Thanks a lot!
Tino

2

OK, this may get a little complicated.

first, have a look at this documentation:

Basically this uses a bunch of planes and calculates if any portion of a bounding box is in that plane.

You can make planes by using points…

OK, so in order to get points, you will need to get 4 rays. I would use the x and y position from the screen and add an extents to it. Say 16 pixels. Next, take each of those rays and get two points from them which correspond to Camera.nearClipPlane and farClipPlane. Now, you will have 8 points. Take two points from each ray, and match it up with 1 point from the next. (4 times over, and that will give you 4 of the 6 planes you need. The other 2 come from the low and high values of the rays.

	Plane[] GetProjection(int x, int y, int extents){
		List<Vector3[]> r = new List<Vector3[]> ();
		r.Add(GetProjection (x - extents, y - extents));
		r.Add(GetProjection (x + extents, y - extents));
		r.Add(GetProjection (x - extents, y + extents));
		r.Add(GetProjection (x + extents, y + extents));

		Plane[] p = new Plane[6];
		p [0] = new Plane (r [0] [0], r [0] [1], r [1] [0]); // top plane
		p [1] = new Plane (r [1] [0], r [1] [1], r [3] [0]); // right plane
		p [0] = new Plane (r [3] [0], r [3] [1], r [2] [0]); // bottom plane
		p [0] = new Plane (r [2] [0], r [2] [1], r [0] [0]); // left plane
		p [0] = new Plane (r [0] [0], r [1] [0], r [2] [0]); // near clip plane
		p [0] = new Plane (r [0] [1], r [1] [1], r [2] [1]); // far clip plane

		return p;
	}

	Vector3[] GetProjection(int x, int y){
		Vector3[] v = new Vector3[2];
		Ray ray = Camera.main.ScreenPointToRay (new Vector3 (x, y, 0));
		v [0] = ray.GetPoint (Camera.main.nearClipPlane);
		v [1] = ray.GetPoint (Camera.main.farClipPlane);
		return v;
	}

Now, with those planes, you can use this:

to test if anything is in them. Then test them for nearest point to the camera or however you want to test them.

3

Have you considered simply using larger colliders?

4

This is close to your solution. Increase the size of colliders proportionate to distance away, but have them at their normal size when closer than a certain distance.

5

Thank you! I’ll try both ideas (bigmisterb’s and the larger colliders). I like the idea of larger colliders directly proportional with growing distance to camera. Especially because my colliders are just triggers, so they do not interfere physically… I will get some issues with my mesh colliders.
Thank you again! It was a great help!

6

It works well with Dameon_'s solution! Thanks a lot!