3D空間上の範囲をPixelで指定する。

NGUIのWidgetのように範囲を指定する機能を最小限で作りたかったので作成

SpriteRendererとは別に範囲を設定するに使えるんじゃないかと思います

Rectangle.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

#if UNITY_EDITOR
using UnityEditor;

[CustomEditor(typeof(Rectangle))]
public class RectangleEditor : Editor{

    SerializedProperty pixelsPerUnitProperty;
    SerializedProperty boundsProperty;

    Rectangle rectangle;

    void OnEnable()
    {
        rectangle = target as Rectangle;
        pixelsPerUnitProperty = serializedObject.FindProperty("pixelsPerUnit");
        boundsProperty = serializedObject.FindProperty("bounds");
    }

    public override void OnInspectorGUI(){
        serializedObject.Update();
        EditorGUILayout.PropertyField(pixelsPerUnitProperty);
        using(new EditorGUILayout.HorizontalScope()){
            GUILayout.FlexibleSpace();
            var oldLabelWidth = EditorGUIUtility.labelWidth;
            EditorGUIUtility.labelWidth = 20;
            int oldWidth = (int)(rectangle.bounds.size.x * rectangle.pixelsPerUnit);
            var width = EditorGUILayout.IntField("W", oldWidth, GUILayout.MaxWidth(100));
            int oldHeight = (int)(rectangle.bounds.size.y * rectangle.pixelsPerUnit);
            var height = EditorGUILayout.IntField("H", oldHeight, GUILayout.MaxWidth(100));

            if(width != oldWidth || height != oldHeight){
                rectangle.bounds.size = new Vector3(width, height, 0f) / rectangle.pixelsPerUnit;
                EditorUtility.SetDirty(rectangle);
            }
            EditorGUIUtility.labelWidth = oldLabelWidth;
        }
        serializedObject.ApplyModifiedProperties();
    }
}
#endif

public class Rectangle : MonoBehaviour {
    public Bounds bounds;

    public int pixelsPerUnit = 100;

    /// <summary>
    /// Callback to draw gizmos that are pickable and always drawn.
    /// </summary>
    void OnDrawGizmos () {
        Gizmos.color = Color.red;
        Gizmos.DrawWireCube (this.transform.position + bounds.center, bounds.size);
    }
}