Instantiate gameobjects at random points on the screen

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Dear fellow programmers

I'm very now to Unity and I was trying to make a boid simulation like Sebastian Lague did (His video). I started with a 2D screen and I want to instantiate 10 boids at random points on the screen.

Here is the code I tried. Located in void Start():

 for (int i=0; i<11; i++) {
             Instantiate(boid);
             boid.transform.position = new Vector2(Random.Range(1, Screen.width), Random.Range(1, Screen.height));
         }

I quickly realised that this is not going to work tho.

The (0, 0) point is at the center of the screen
I can't just take screen coordinates and convert them into world coordinates

I tried to put my vector2 in Camera.main.WorldToScreenPoint(). But it didn't work. It even put the object further away from the screen.

I did some extensive research over a few days. But I didn't find anything helpful.

I somehow excpected there is an easyer way to convert screen pixels to world coordinated. Like there is a multiplication factor or something.

Anyway I hope I was clear. If you have any more questions feel free to ask and thanks for your help in advance.

Answer 1

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Answer by The-Peaceful · Apr 26, 2021 at 08:58 AM

You use Camera.main.WorldToScreenPoint(), that would give you the opposite of what you want (world point to a point in pixel space), what you want is Camera.main.ScreenToWorldPoint() :D The point (0,0) then is at the bottom left of the screen, as you can read in the documentation (link below)

https://docs.unity3d.com/ScriptReference/Camera.ScreenToWorldPoint.html

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ShadowCrafter_01_Hello · Apr 26, 2021 at 10:54 AM 0

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Ok so thats working. Thanks so much. But there is still a little bit of a weird problem. All the boids had a z value of -10. So the were not visible in the game view. I checked that the prefab value was set to 0 and it was. I applied a little bit of a crude fix and manually set all the boids z value to 0 in the code. But do you have any idea what could cause the boids to be instantiated at -10?

The-Peaceful ShadowCrafter_01_Hello · Apr 26, 2021 at 02:49 PM 0

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That's probably because the camera has a Z position of -10, so when you tell it to transform the 2D position into 3D world space, it just takes that value as the Z component of the vector. So setting it to 0 afterwards is just the right way to do it. :D

ShadowCrafter_01_Hello The-Peaceful · Apr 27, 2021 at 05:39 AM 0

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Ok thank you so much for your help :)

Instantiate gameobjects at random points on the screen

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