代码定位到Shadow和Outline的主要实现代码：

//Shadow的实现
public override void ModifyMesh(VertexHelper vh)
        {
            if (!IsActive())
                return;

            var output = ListPool<UIVertex>.Get();
            vh.GetUIVertexStream(output);

            ApplyShadow(output, effectColor, 0, output.Count, effectDistance.x, effectDistance.y);
            vh.Clear();
            vh.AddUIVertexTriangleStream(output);
            ListPool<UIVertex>.Release(output);
        }

//Outline的实现
public override void ModifyMesh(VertexHelper vh)
        {
            if (!IsActive())
                return;

            var verts = ListPool<UIVertex>.Get();
            vh.GetUIVertexStream(verts);

            var neededCpacity = verts.Count * 5;
            if (verts.Capacity < neededCpacity)
                verts.Capacity = neededCpacity;

            var start = 0;
            var end = verts.Count;
            ApplyShadowZeroAlloc(verts, effectColor, start, verts.Count, effectDistance.x, effectDistance.y);

            start = end;
            end = verts.Count;
            ApplyShadowZeroAlloc(verts, effectColor, start, verts.Count, effectDistance.x, -effectDistance.y);

            start = end;
            end = verts.Count;
            ApplyShadowZeroAlloc(verts, effectColor, start, verts.Count, -effectDistance.x, effectDistance.y);

            start = end;
            end = verts.Count;
            ApplyShadowZeroAlloc(verts, effectColor, start, verts.Count, -effectDistance.x, -effectDistance.y);

            vh.Clear();
            vh.AddUIVertexTriangleStream(verts);
            ListPool<UIVertex>.Release(verts);
        }

两者其实都是复制网格顶点并指定方向距离进行绘制，也就是说Shadow和Outline的实现是通过增加顶点数据实现的，两者都重写了ModifyMesh方法，但Outline继承了Shadow，Outline增加的顶点数是Shadow的5倍，所以要慎用

Unity提供了BaseMeshEffect类，它继承自IMeshModifier，可以重写public override void ModifyMesh(VertexHelper helper)方法修改Mesh，贴图等数据