2 enjoy yuan mode

The flyweight pattern

The flyweight pattern ： Multiple instances with similar functions , Share a public instance .

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The explanation in the book ：

We need to render a forest , There are a thousand trees in the forest , Every tree has the same part ： Grid of trees 、 The texture of trees and leaves
Each tree has different parts ： Location 、 rotate 、 Zoom, etc

Encapsulate the same part into a class , Instantiate only once ; Different parts are encapsulated into a class , Instantiate a thousand times .

stay Direct3D and openGL The graphic API in , Provide separately
The first is the public data block that will be rendered many times —— Instances of classes of shared trees
The second is the instance list and its parameters —— An example of a thousand trees （ Contains different locations 、 rotate 、 The zoom ）

This renders a forest

The use trace of Xiangyuan mode is not obvious , If you do not additionally encapsulate a class shared between multiple instances , This seems to be resource sharing .

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stay 1 Command mode in , Jump commands are purely behavioral, stateless records , under these circumstances , There are multiple instances of jump command classes , It's a waste of memory , Because all instances are functionally equivalent .

Flyweight （ Enjoying yuan ） Pattern solved “ Instantiating multiple instances with the same function wastes memory ” This problem .
The solution is to let multiple similar instances share an instance of a class

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How to use the sharing mode ？

Illustrate with examples , Create a 2D World class , Generate an instance of the world class later

	public class World
    {
    
        public List<Terrain> terrainList = new List<Terrain>();
        public TerrainProp grassProp = new TerrainProp(1, false, Texture.GRASS_TEXTURE);
        public TerrainProp hillProp = new TerrainProp(3, false, Texture.HILL_TEXTURE);
        public TerrainProp riverProp = new TerrainProp(2, true, Texture.RIVER_TEXTURE);
    }

There are terrain classes in the world class , The data in the terrain category is divided into two parts ：
Part is the position of the terrain instance in the world , Each terrain instance should be in a different position in the world , This part is different for each instance 、 Unshareable ;

	public class Terrain
    {
    
        #region  Unshareable parts 
        //  The position of the lower left vertex of the terrain block in the world 
        public int x;
        public int y;
        public int width = 10;
        public int height = 10;
        #endregion
        #region  The shared part 
        public TerrainProp prop;
        #endregion
        public Terrain(int x, int y, TerrainProp prop)
        {
    
            this.x = x;
            this.y = y;
            this.prop = prop;
        }
    }

The example in the book is to store the terrain in the form of an array into the member attribute of the world class , Therefore, the index of the array directly represents the location of the terrain , There are only shareable parts left between different terrains

The other part is the characteristics of terrain instances , for example “ Moving speed on the terrain ”、“ Whether this terrain is navigable ”、“ The map of this terrain ” Such a characteristic , This part can be used in the same type of terrain instances Shareable .

	public class TerrainProp
    {
    
        public int moveSpeed;
        public bool isWater;
        public Texture texture;
        public TerrainProp(int moveSpeed, bool isWater, Texture texture)
        {
    
            this.moveSpeed = moveSpeed;
            this.isWater = isWater;
            this.texture = texture;
        }
    }
    public class Texture
    {
    
        public static Texture GRASS_TEXTURE;
        public static Texture HILL_TEXTURE;
        public static Texture RIVER_TEXTURE;
    }

Last , When generating multiple terrain instances of the world , The same type of terrain shares the same terrain attribute TerrainProp

		public void GenerateWorld()
        {
    
            terrainList.Clear();
            //  Generate   Two lawns 、 Two hills 、 The two rivers are arranged horizontally 
            for (int i = 0; i < 6; i++)
            {
    
                TerrainProp tmp;
                if (i < 2)
                {
    
                    tmp = grassProp;
                }
                else if (i < 4)
                {
    
                    tmp = hillProp;
                }
                else
                {
    
                    tmp = riverProp;
                }
                var terrain = new Terrain(i * 10, 0, tmp);
                terrainList.Add(terrain);
            }
        }