1_demo.gif

2_SegmentationDrawer.cs

using System;
using System.Collections.Generic;
using UnityEditor;
using UnityEditor.UIElements;
using UnityEngine;
using UnityEngine.UIElements;

[CustomEditor(typeof(SegmentedStuff))]
public class SegmentationDrawer : Editor
{
    private struct SerializedFloatArrayProperty
    {
        public readonly SerializedProperty property;

        public int arraySize => property.arraySize;

        public SerializedFloatArrayProperty(SerializedProperty property)
        {
            if(! property.isArray) throw new ArgumentException();
            this.property = property;
        }

        public void RemoveAt(int index)
        {
            property.DeleteArrayElementAtIndex(index);
        }
        
        public void Insert(int index, float value)
        {
            property.InsertArrayElementAtIndex(index);
            property.GetArrayElementAtIndex(index).floatValue = value;
        }
        
        public float this[int index]
        {
            get => property.GetArrayElementAtIndex(index).floatValue;
            set => property.GetArrayElementAtIndex(index).floatValue = value;
        }
    }

    
    private readonly List<Box> boxes = new List<Box>();
    private VisualElement root;
    private SerializedFloatArrayProperty floatValues;
    
    private void OnEnable() {
        floatValues = new SerializedFloatArrayProperty(serializedObject.FindProperty("floatValues"));

        float sum = 0.0f;
        for (int i = 0; i < floatValues.arraySize; ++i) sum += floatValues[i];
        for (int i = 0; i < floatValues.arraySize; ++i) floatValues[i] /= sum;
    }

    private int separatorIndex;

    private void AddSeparator(int index, VisualElement container) {
        var separator = new Box();
        separator.AddToClassList("separator");
        void DragResize(MouseMoveEvent evt) {
            var dx = evt.mouseDelta.x / container.contentRect.width;
            
            var fx = Mathf.Min( floatValues[separatorIndex] + dx, 0);
            fx = Mathf.Min(floatValues[separatorIndex+1] - dx, fx);

            dx += fx * Mathf.Sign(dx);
            
            floatValues[separatorIndex] += dx;
            floatValues[separatorIndex+1] -= dx;

            floatValues[separatorIndex] = Mathf.RoundToInt(floatValues[separatorIndex] * 1000) / 1000f;
            floatValues[separatorIndex+1] = Mathf.RoundToInt(floatValues[separatorIndex+1] * 1000) / 1000f;
            
            UpdateSizes();
        }
        
        separator.RegisterCallback<MouseDownEvent>(evt => {
            separatorIndex = index;
            container.RegisterCallback<MouseMoveEvent>(DragResize);
        });
        container.RegisterCallback<MouseUpEvent>(evt => {
            separatorIndex = -1;
            container.UnregisterCallback<MouseMoveEvent>(DragResize);
        });
        container.RegisterCallback<MouseLeaveEvent>(evt => {
            separatorIndex = -1;
            container.UnregisterCallback<MouseMoveEvent>(DragResize);
        });
        container.Add(separator);
    }

    
    
    private void UpdateSizes() {
        float sum = 0.0f;
        for (int i = 0; i < floatValues.arraySize; ++i) sum += floatValues[i];
        for (int i = 0; i < floatValues.arraySize; ++i) floatValues[i] /= sum;

        if (boxes.Count != floatValues.arraySize)
        {
            root.RemoveAt(0);
            root.Insert(0, CreateContent());
            return;
        }
        
        for (var i = 0; i < boxes.Count; i++) {
            boxes[i].style.flexGrow = floatValues[i];
            boxes[i].Q<Label>().text = $"{floatValues[i]:P}";
        }
        if(serializedObject.targetObject != null) // can happen with multiple inspectors
            serializedObject.ApplyModifiedProperties();
    }

    VisualElement CreateContent()
    {
        var container = new BindableElement();
        container.BindProperty(floatValues.property);
        
        container.style.flexDirection = FlexDirection.Row;
        boxes.Clear();
        for (int i = 0; i < floatValues.arraySize; ++i) {
            var b = new Box();
            var l = new Label(string.Empty);
            b.Add(l);
            boxes.Add(b);

            int j = i;
            
            b.RegisterCallback<MouseDownEvent>(evt => {
                if(evt.button != 0) return;
                if (evt.shiftKey && !evt.ctrlKey) {
                    floatValues[j] /= 2;
                    floatValues.Insert(j, floatValues[j]);
                    root.RemoveAt(0);
                    root.Insert(0, CreateContent());
                }
                if (!evt.shiftKey && evt.ctrlKey) {
                    if (floatValues.arraySize > 1) {
                        int n = j == 0 ? 1 : j - 1;
                        floatValues[n] += floatValues[j];
                        floatValues.RemoveAt(j);
                        root.RemoveAt(0);
                        root.Insert(0, CreateContent());
                    }
                    
                }
                
            });
        }
        
        UpdateSizes();
        container.Add(boxes[0]);
        for (int i = 1; i < boxes.Count; ++i) {
            AddSeparator(i - 1, container);
            container.Add(boxes[i]);
        }

        return container;
    }
    
    public override VisualElement CreateInspectorGUI()
    {
        root = new VisualElement();
        root.Bind(serializedObject);
        
        root.styleSheets.Add(AssetDatabase.LoadAssetAtPath<StyleSheet>("Assets/_Gyms/SegmentationDrawer/Editor/SegmentationDrawerStyle.uss"));
        root.Add(CreateContent());
            
        root.Add(new Label("Shift-Click to split segment in two"));
        root.Add(new Label("Ctrl-Click to delete segment"));


        var action = root.schedule.Execute(UpdateSizes);
        action.Every(100); // ms
        
        return root;
    }
    
}

3_SegmentationStuff.cs

using UnityEngine;

public class SegmentedStuff : MonoBehaviour {

    public float[] floatValues = new []{1f, 1f, 1f}; // some default values, don't make it empty
}

SegmentationDrawerStyle.uss

.unity-box{
    height: 30;
    flex-grow: 1;
    flex-basis: 7;
    justify-content: center;
}

.unity-box > Label{
    -unity-text-align: middle-center;
    overflow: hidden;
    font-size: 8;
}

.unity-box:hover{
    -unity-background-image-tint-color: #eeeeff;
}   

.unity-box.separator{
    flex-grow: 0;
    flex-basis: 7;
    margin: 0 -3;
    cursor: split-resize-left-right;
    background-image: none;
}