Set a Material's main texture with a sprite.

SetMaterialWithSpriteEditorWindow.cs

// The MIT License (MIT) - https://gist.github.com/bcatcho/1926794b7fd6491159e7
// Copyright (c) 2015 Brandon Catcho
using UnityEngine;
using UnityEditor;

namespace CatchCo.EditorScripts.Util
{
   public class SetMaterialWithSpriteEditorWindow : EditorWindow
   {
      private Material _material;
      private bool _needsPositionUpdated;
   
      // Add a menu item called "Double Mass" to a Rigidbody's context menu.
      [MenuItem ("CONTEXT/Material/Set With Sprite")]
      static void SetToSprite(MenuCommand command)
      {
         var rect = new Rect(0, 0, 100f, 100f);
         var window = EditorWindow.GetWindowWithRect<SetMaterialWithSpriteEditorWindow>(rect, false, "Set With Sprite", true);
         window._material = (Material)command.context;
         window._needsPositionUpdated = true;
      }
   
      public void OnGUI()
      {
         // first OnGUI, set the window to where the mouse is
         if (_needsPositionUpdated)
         {
            var screenPos = GUIUtility.GUIToScreenPoint(Event.current.mousePosition);
            position = new Rect(screenPos.x, screenPos.y, 100f, 100f);
            _needsPositionUpdated = false;
         }
         
         // Set a ridiculous color to make it noticeable
         var previousColor = GUI.backgroundColor;
         GUI.backgroundColor = new Color32(255, 98, 95, 255);
         if (GUILayout.Button("Choose sprite", GUILayout.ExpandWidth(true), GUILayout.ExpandHeight(true)))
         {
            ShowPicker();
         }
         GUI.backgroundColor = previousColor;
   
         if (Event.current.commandName == "ObjectSelectorUpdated")
         {
            var sprite = (Sprite)EditorGUIUtility.GetObjectPickerObject();
            UpdateWithSprite(sprite);
         }
   
         if (Event.current.keyCode == KeyCode.Escape || Event.current.commandName == "ObjectSelectorClosed")
         {
            Close();
         }
      }
   
      private void ShowPicker()
      {
         int controlID = EditorGUIUtility.GetControlID(FocusType.Passive);
         EditorGUIUtility.ShowObjectPicker<Sprite>(null, false, "", controlID);
      }
      
      private void UpdateWithSprite(Sprite sprite)
      {
         if (sprite == null)
            return;
   
         var rect = sprite.textureRect;
         var texSize = new Vector2(sprite.texture.width, sprite.texture.height);
         var tiling = new Vector2(rect.width / texSize.x, rect.height / texSize.y);
         var offset = new Vector2(rect.x / texSize.x, rect.y / texSize.y);
   
         _material.mainTextureOffset = offset;
         _material.mainTextureScale = tiling;
         _material.mainTexture = sprite.texture;
      }
   }
}