CubeMap.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SortRenderWithCSharp {
    /// <summary>
    /// 立方体纹理,
    /// 拥有六个面的纹理,
    /// 通过3D向量进行采样,从该立方体中心出发的向量与任意一个面的交点即为采样点
    /// </summary>
    public class CubeMap {
        // 纹理数组
        // 纹理顺序是 
        // front,back,left,right,top,bottom
        private Bitmap[] textures;
        // 用于采样的六个面,顺序与纹理顺序一致
        private Plane[] planes;

        public Bitmap[] Textures { get => textures; set => textures = value; }
        public Plane[] Planes { get => planes; set => planes = value; }

        public CubeMap(Bitmap frontTexture,Bitmap backTexture, Bitmap leftTexture, Bitmap rightTexture,Bitmap topTexture,Bitmap bottomTexture) {
            // 初始化立方体的六个平面
            Plane front = new Plane(new Vector3(0,0,-1),new Vector3(-1,-1,-1));
            Plane back = new Plane(new Vector3(0,0,1),new Vector3(-1,-1,1));
            Plane left = new Plane(new Vector3(-1,0,0),new Vector3(-1,-1,-1));
            Plane right = new Plane(new Vector3(1,0,0),new Vector3(1,-1,-1));
            Plane top = new Plane(new Vector3(0,1,0),new Vector3(-1,1,-1));
            Plane bottom = new Plane(new Vector3(0,-1,0),new Vector3(-1,-1,-1));

            planes = new Plane[]{
                front,back,left,right,top,bottom    
            };

            Textures = new Bitmap[] {
                frontTexture,backTexture,leftTexture,rightTexture,topTexture,bottomTexture
            };
        }

        /// <summary>
        /// 根据一个从立方体中心出发的方向向量来对立方体纹理进行采样,
        /// 该方向向量必须为归一化的向量
        /// </summary>
        /// <param name="cubeMap"></param>
        /// <param name="dir"></param>
        /// <returns></returns>
        public static Color01 TexCube(CubeMap cubeMap,Vector3 dir) {

            // 用于采样的射线
            Ray ray = new Ray(Vector3.Zero,dir,10f);

            // 分别于判断该射线与6个面的相交情况,如果与任意一个面相交,那么根据交点进行采样
            for (int i=0;i<6;i++) {
                Plane plane = cubeMap.Planes[i];

                float u, v = 0;

                // 如果相交,那么根据交点进行采样
                if (Ray.GetIntersectionPoint(ray, plane, out Vector3 point)) {
                    switch (i) {
                        case 0:
                        case 1:
                            // front、back,即xy空间
                            u = point.X * 0.5f + 0.5f;
                            v = point.Y * 0.5f + 0.5f;
                            return Texture.Tex2D(cubeMap.Textures[i],u,v);
                        case 2:
                            // left、right，即yz平面
                            u = point.Z * 0.5f + 0.5f;
                            v = point.Y * 0.5f + 0.5f;
                            return Texture.Tex2D(cubeMap.Textures[i], u, v);
                        case 4:
                        case 5:
                            // top、bottom,即xz平面
                            u = point.X * 0.5f + 0.5f;
                            v = point.Z * 0.5f + 0.5f;
                            return Texture.Tex2D(cubeMap.Textures[i], u, v);
                    }
                }
            }

            return Color01.White;
        }
    }
}