BoxColliderEditFaceCenterDots makes resizing BoxColiders easy

BoxColliderEditFaceCenterDots.cs

#if UNITY_EDITOR
using System;
using System.Collections.Generic;
using UnityEditor;
using UnityEditor.EditorTools;
using UnityEngine;
using UnityEngine.Rendering;

/// <summary>
/// While Unity’s built-in box collider edit tool is active, draws camera-facing 
/// discs at each face center (X red, Y blue, Z green, alpha 1). 
/// </summary>
[InitializeOnLoad]
static class BoxColliderEditFaceCenterDots {
    static readonly Color FaceColorX = new Color(1f, 0f, 0f, 1f);
    static readonly Color FaceColorY = new Color(0f, 1f, 0f, 1f);
    static readonly Color FaceColorZ = new Color(0f, 0f, 1f, 1f);
    const float DotSizeFactor = 0.09f;

    static Type _boxPrimitiveColliderToolType;

    static BoxColliderEditFaceCenterDots() => SceneView.duringSceneGui += OnSceneGUI;

    static void OnSceneGUI(SceneView view) {
        if (!IsBoxPrimitiveColliderToolActive())
            return;

        var targets = CollectSelectedBoxColliders();
        if (targets.Count == 0)
            return;

        var cam = view.camera;

        var prevZ = Handles.zTest;
        Handles.zTest = CompareFunction.Always;

        foreach (var box in targets) {
            if (box == null)
                continue;
            DrawFaceCenterDots(box, cam);
        }

        Handles.zTest = prevZ;
    }

    static void DrawFaceCenterDots(BoxCollider box, Camera cam) {
        Transform t = box.transform;
        Vector3 c = box.center;
        Vector3 h = box.size * 0.5f;
        (Vector3 local, Color color)[] faces = {
            (c + new Vector3(h.x, 0f, 0f), FaceColorX),
            (c + new Vector3(-h.x, 0f, 0f), FaceColorX),
            (c + new Vector3(0f, h.y, 0f), FaceColorY),
            (c + new Vector3(0f, -h.y, 0f), FaceColorY),
            (c + new Vector3(0f, 0f, h.z), FaceColorZ),
            (c + new Vector3(0f, 0f, -h.z), FaceColorZ),
        };

        foreach (var (local, color) in faces) {
            Vector3 world = t.TransformPoint(local);
            float radius = HandleUtility.GetHandleSize(world) * DotSizeFactor * 0.75f;
            Vector3 normal = cam != null ? (cam.transform.position - world).normalized : Vector3.forward;
            if (normal.sqrMagnitude < 1e-10f)
                normal = Vector3.up;
            Handles.color = color;
            Handles.DrawSolidDisc(world, normal, radius);
        }
    }

    static List<BoxCollider> CollectSelectedBoxColliders() {
        var set = new HashSet<BoxCollider>();
        foreach (var o in Selection.objects) {
            switch (o) {
                case BoxCollider b:
                    set.Add(b);
                    break;
                case GameObject go:
                    if (go.TryGetComponent(out BoxCollider b2))
                        set.Add(b2);
                    break;
            }
        }

        return new List<BoxCollider>(set);
    }

    static bool IsBoxPrimitiveColliderToolActive() {
        if (_boxPrimitiveColliderToolType == null)
            _boxPrimitiveColliderToolType = FindBoxPrimitiveColliderToolType();
        return _boxPrimitiveColliderToolType != null && ToolManager.activeToolType == _boxPrimitiveColliderToolType;
    }

    static Type FindBoxPrimitiveColliderToolType() {
        var t = Type.GetType("UnityEditor.BoxPrimitiveColliderTool, UnityEditor");
        if (t != null)
            return t;
        foreach (var asm in AppDomain.CurrentDomain.GetAssemblies()) {
            t = asm.GetType("UnityEditor.BoxPrimitiveColliderTool");
            if (t != null)
                return t;
        }

        return null;
    }
}
#endif