Unity3D如何实现渐变颜色效果

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
 
namespace ExtraFoundation.Components
{
 [AddComponentMenu("UI/Effects/Gradient")]
 public class UIGradient : BaseMeshEffect
 {
 #region Public Declarations
 public enum Type
 {
 Vertical,
 Horizontal
 }
 #endregion
 
 #region Public Properties
 public Type GradientType = Type.Vertical;
 [Range(-1f, 1f)]
 public float Offset = 0f;
 public Gradient gradient;
 #endregion
 
 #region Public Methods
 public override void ModifyMesh(VertexHelper helper)
 {
 if (!IsActive() || helper.currentVertCount == 0)
 {
 return;
 }
 
 vertexList.Clear();
 helper.GetUIVertexStream(vertexList);
 
 int nCount = vertexList.Count;
 switch (GradientType)
 {
 case Type.Vertical:
  {
  float fBottomY = vertexList[0].position.y;
  float fTopY = vertexList[0].position.y;
  float fYPos = 0f;
 
  for (int i = nCount - 1; i >= 1; --i)
  {
  fYPos = vertexList[i].position.y;
  if (fYPos > fTopY)
  fTopY = fYPos;
  else if (fYPos < fBottomY)
  fBottomY = fYPos;
  }
 
  float fUIElementHeight = 1f / (fTopY - fBottomY);
  UIVertex v = new UIVertex();
 
  for (int i = 0; i < helper.currentVertCount; i++)
  {
  helper.PopulateUIVertex(ref v, i);
  v.color = gradient.Evaluate((v.position.y - fBottomY) *
  fUIElementHeight - Offset);
  helper.SetUIVertex(v, i);
  }
  }
  break;
 case Type.Horizontal:
  {
  float fLeftX = vertexList[0].position.x;
  float fRightX = vertexList[0].position.x;
  float fXPos = 0f;
 
  for (int i = nCount - 1; i >= 1; --i)
  {
  fXPos = vertexList[i].position.x;
  if (fXPos > fRightX)
  fRightX = fXPos;
  else if (fXPos < fLeftX)
  fLeftX = fXPos;
  }
 
  float fUIElementWidth = 1f / (fRightX - fLeftX);
  UIVertex v = new UIVertex();
 
  for (int i = 0; i < helper.currentVertCount; i++)
  {
  helper.PopulateUIVertex(ref v, i);
  v.color = gradient.Evaluate((v.position.x - fLeftX) *
  fUIElementWidth - Offset);
  helper.SetUIVertex(v, i);
  }
 
  }
  break;
 default:
  break;
 }
 }
 #endregion
 
 #region Internal Fields
 private List vertexList = new List();
 #endregion
 }
}