MinMaxSlider

MinMaxSliderAttribute.cs

using UnityEngine;
using System.Collections;

public class MinMaxSliderAttribute : PropertyAttribute
{
    public readonly float max;
    public readonly float min;

    public MinMaxSliderAttribute(float min, float max)
    {
        this.min = min;
        this.max = max;
    }
}

MinMaxSliderDrawer.cs

using UnityEngine;
using UnityEditor;

// based on: https://gist.github.com/frarees/9791517
[CustomPropertyDrawer(typeof(MinMaxSliderAttribute))]
class MinMaxSliderDrawer : PropertyDrawer
{
    /// <summary>インデント段階を保存</summary>
    private int lastIndentLevel;

    /// <summary>インデント量</summary>
    private int indentAmount;

    /// <summary>描画領域全体</summary>
    private Rect wholeRect;

    /// <summary>ラベルの幅</summary>
    private const float LabelWidth = 60;

    /// <summary>ラベルの間隔</summary>
    private const float LabelMargin = 5;


    /// <summary>
    /// 描画を行う
    /// </summary>
    /// <param name="position">描画範囲</param>
    /// <param name="property">対象プロパティ</param>
    /// <param name="label">表示するラベル</param>
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        BeginProperty(position, property, label);

        // Vector2のみ対応
        if (property.propertyType == SerializedPropertyType.Vector2)
        {
            // 値の取得
            Vector2 range = property.vector2Value;
            float min = range.x;
            float max = range.y;
            MinMaxSliderAttribute attr = attribute as MinMaxSliderAttribute;
            EditorGUI.BeginChangeCheck();

            var rect = this.wholeRect;

            // min field
            rect.width = LabelWidth;
            min = EditorGUI.FloatField(rect, min);
            min = Mathf.Clamp(min, attr.min, max);

            // min max slider
            rect.x += LabelWidth + LabelMargin;
            rect.width = this.wholeRect.width - LabelWidth * 2 - LabelMargin * 2;
            EditorGUI.MinMaxSlider(new GUIContent(), rect, ref min, ref max, attr.min, attr.max);

            // max field
            rect.x += this.wholeRect.width - LabelWidth * 2 - LabelMargin;
            rect.width = LabelWidth;
            max = EditorGUI.FloatField(rect, max);
            max = Mathf.Clamp(max, min, attr.max);

            // 変更の適用
            if (EditorGUI.EndChangeCheck())
            {
                range.x = min;
                range.y = max;
                property.vector2Value = range;
            }
        }
        else
        {
            EditorGUI.LabelField(position, label, "Use only with Vector2");
        }

        EndProperty();
    }

    /// <summary>
    /// プロパティの開始
    /// </summary>
    /// <param name="position">OnGUIと同じ</param>
    /// <param name="property">OnGUIと同じ</param>
    /// <param name="label">OnGUIと同じ</param>
    protected void BeginProperty(Rect position, SerializedProperty property, GUIContent label)
    {
        this.indentAmount = EditorGUI.indentLevel * 16;

        EditorGUIUtility.labelWidth = EditorGUIUtility.labelWidth;
        label = EditorGUI.BeginProperty(position, label, property);

        this.lastIndentLevel = EditorGUI.indentLevel;
        this.wholeRect = EditorGUI.PrefixLabel(position, label);
        EditorGUI.indentLevel = 0;
    }

    /// <summary>
    /// プロパティの終了
    /// </summary>
    protected void EndProperty()
    {
        EditorGUI.indentLevel = this.lastIndentLevel;
        EditorGUI.EndProperty();
    }
}

Test.cs

using UnityEngine;
using System.Collections;

public class Test : MonoBehaviour 
{
    [MinMaxSlider(0, 255)]
    public Vector2 range;
}

Awesome script, thanks for sharing.