How to do selection box ?

like in starcraft 2, you want to select multiple units, you can drag and draw a box to select all units in the box. But starcraft in 2D, i want to do in 3D space, something like HomeWorld, i dont need codes, i just need ideas, you can rotates your camera anywhere while still allows to do the selection.

 

I would draw the selection box in a Canvas associated with the camera. And then just highlight whatever units fall within the corresponding part of the screen.

 

I think i can draw on the canvas, but how do i know if which units are in that box ? that box is on canvas and has no direct relation to the 3d space.

 

https://docs.unity3d.com/ScriptReference/Camera.WorldToViewportPoint.html
&
https://docs.unity3d.com/ScriptReference/Camera.WorldToScreenPoint.html

Hey, how would we do this without needing to calculate the viewport or screen point of everything we want select-able? I could do this easily by getting those points, and then running them through an if then block to cull those that fall outside two further points defined by a click-drag function.

 

Yep, that's how you do it.

 

that means if there are like 100 units on the 3d space, i need to perform the calculation for every single units to see if they are within the selection box ?

 

Yep. And you also need to quit worrying about it. 100 coordinate transformations and bounds checks is trivial compared to what routinely happens on every frame anyway (particularly when physics are involved). And you'll be doing this only during manual selection.

There are certainly ways to optimize it if profiling later shows this to be a bottleneck. But I doubt it will ever show that.

 

actually i will need to do that every frame, imagine when you are dragging the box, you need to highlight which units will be selected, not only upon mouse up. thats why i am worry if the calculation will be heavy.

 

Yes, that's why I said "during manual selection" (instead of "at the end of manual selection").

Well please stop.

 

Don't worry. Just build it and see what happens. If it is to heavy, then come back and we can help optimize.

 

Not doing anything yet, just planning and predicting problems or difficulties.

 

That's a slippery slope that often leads to analysis paralysis (not saying that no analysis should be done, just don't overdo it).
Since building proof of concept scenes in Unity is extremely easy, if you're worried about the performance, commit a couple of hours and build it up. In many cases you will end up with a code snippet that is actually functional enough for the prototype/first iterations.
But the biggest boon of building a PoC like that, is that if it works, you can stop worrying about it - and that's very important. When designing complex systems crossing anything out of "need to keep in mind to figure out" is invaluable, as our minds tend to jump between unsolved things, creating distractions and leading to us jumping between things we work on (and, usually, multi-tasking developers tend to create sloppy, duct-tape solutions).

 

This is an old post, but when I was looking for a solution to get a selection rectangle drawing in game mode, also in a build version, then there were not really satisfying answers. Most tried via some assets packages or either Line Renderer or Shaders, which I found to be overloaded for what I was trying to achieve.

I finally managed to build it myself with very few code and want to share for everyone else googling in the future, enjoy:

Code (CSharp):

1.  
2. using UnityEngine;
3. /// <summary>
4. /// Draws a selection rectangle on the left mouse button down & dragging
5. ///
6. /// You only need an InputReceiverManager that basically tracks
7. /// - if the left mouse button is currently down and saves it in "LeftMouseButtonDown"
8. /// - saves the initial click position when mouse button was clicked  and saves it in "InitialMousePositionOnLeftClick"
9. /// - updates the current mouse position and saves it in "CurrentMousePosition"
10. ///
11. /// </summary>
12. public class SelectionRectangleDrawer : MonoBehaviour
13. {
14.     //set color via inspector for the selection rectangles filler color
15.     public Color SelectionRectangleFillerColor;
16.     //set color via inspector for the selection rectangles border color
17.     public Color SelectionRectangleBorderColor;
18.     //set selection rectangles  border thickness
19.     public int SelectionRectangleBorderThickness = 2;
20.     private Texture2D _selectionRectangleFiller;
21.     private Texture2D _selectionRectangleBorder;
22.     private bool _drawSelectionRectangle;
23.     private float _x1, _x2, _y1, _y2;
24.     private Vector2 pos1, pos2;
25.     void Start()
26.     {
27.         _selectionRectangleFiller = new Texture2D(1, 1);
28.         _selectionRectangleFiller.SetPixel(0, 0, SelectionRectangleFillerColor);
29.         _selectionRectangleFiller.Apply();
30.         _selectionRectangleFiller.wrapMode = TextureWrapMode.Clamp;
31.         _selectionRectangleFiller.filterMode = FilterMode.Point;
32.         _selectionRectangleBorder = new Texture2D(1, 1);
33.         _selectionRectangleBorder.SetPixel(0, 0, SelectionRectangleBorderColor);
34.         _selectionRectangleBorder.Apply();
35.         _selectionRectangleBorder.wrapMode = TextureWrapMode.Clamp;
36.         _selectionRectangleBorder.filterMode = FilterMode.Point;
37.     }
38.     void Update()
39.     {
40.         if (InputReceiverManager.Instance.LeftMouseButtonDown && !Mathf.Approximately(Vector2.Distance(InputReceiverManager.Instance.CurrentMousePosition,
41.                                                                                                        InputReceiverManager.Instance.InitialMousePositionOnLeftClick), 0f))
42.             _drawSelectionRectangle = true;
43.         else if (!InputReceiverManager.Instance.LeftMouseButtonDown && _drawSelectionRectangle)
44.             _drawSelectionRectangle = false;
45.     }
46.     private void OnGUI()
47.     {
48.         if (_drawSelectionRectangle)
49.             drawSelectionRectangle();
50.     }
51.     private void drawSelectionRectangle()
52.     {
53.         pos1 = InputReceiverManager.Instance.InitialMousePositionOnLeftClick;
54.         pos2 = InputReceiverManager.Instance.CurrentMousePosition;
55.         //check initial mouse position on X axis versus dragging mouse position
56.         if (pos1.x < pos2.x)
57.         {
58.             _x1 = pos1.x;
59.             _x2 = pos2.x;
60.         }
61.         else
62.         {
63.             _x1 = pos2.x;
64.             _x2 = pos1.x;
65.         }
66.         //check initial mouse position on Y axis versus dragging mouse position
67.         if (pos1.y < pos2.y)
68.         {
69.             _y1 = pos1.y;
70.             _y2 = pos2.y;
71.         }
72.         else
73.         {
74.             _y1 = pos2.y;
75.             _y2 = pos1.y;
76.         }
77.         //filler
78.         GUI.DrawTexture(new Rect(_x1, Screen.height - _y1, _x2 - _x1, _y1 - _y2), _selectionRectangleFiller, ScaleMode.StretchToFill);
79.         //top line
80.         GUI.DrawTexture(new Rect(_x1, Screen.height - _y1, _x2 - _x1, -SelectionRectangleBorderThickness), _selectionRectangleBorder, ScaleMode.StretchToFill);
81.         //bottom line
82.         GUI.DrawTexture(new Rect(_x1, Screen.height - _y2, _x2 - _x1, SelectionRectangleBorderThickness), _selectionRectangleBorder, ScaleMode.StretchToFill);
83.         //left line
84.         GUI.DrawTexture(new Rect(_x1, Screen.height - _y1, SelectionRectangleBorderThickness, _y1 - _y2), _selectionRectangleBorder, ScaleMode.StretchToFill);
85.         //right line
86.         GUI.DrawTexture(new Rect(_x2, Screen.height - _y1, -SelectionRectangleBorderThickness, _y1 - _y2), _selectionRectangleBorder, ScaleMode.StretchToFill);
87.     }
88. }
89.  
90.  
91.