MonoGame.Samples/TexturedQuad/Core/Quad.cs

using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace TexturedQuad.Core
{
    public struct Quad
    {
        public Vector3 Origin;
        public Vector3 UpperLeft;
        public Vector3 LowerLeft;
        public Vector3 UpperRight;
        public Vector3 LowerRight;
        public Vector3 Normal;
        public Vector3 Up;
        public Vector3 Left;
        public VertexPositionNormalTexture[] Vertices;
        public short[] Indexes;

        /// <summary>
        /// Initializes a new quad with the specified origin, normal, up vector, width, and height.
        /// Calculates the quad's corners and fills the vertex and index buffers.
        /// </summary>
        /// <param name="origin">The center of the quad.</param>
        /// <param name="normal">The normal vector of the quad's surface.</param>
        /// <param name="up">The up direction for the quad.</param>
        /// <param name="width">The width of the quad.</param>
        /// <param name="height">The height of the quad.</param>
        public Quad(Vector3 origin, Vector3 normal, Vector3 up, float width, float height)
        {
            Vertices = new VertexPositionNormalTexture[4];
            Indexes = new short[6];
            Origin = origin;
            Normal = normal;
            Up = up;
            Left = Vector3.Cross(normal, Up);
            Vector3 uppercenter = (Up * height / 2) + origin;
            UpperLeft = uppercenter + (Left * width / 2);
            UpperRight = uppercenter - (Left * width / 2);
            LowerLeft = UpperLeft - (Up * height);
            LowerRight = UpperRight - (Up * height);
            FillVertices();
        }

        /// <summary>
        /// Fills the quad's vertex and index buffers with positions, normals, and texture coordinates.
        /// </summary>
        private void FillVertices()
        {
            Vector2 textureUpperLeft = new Vector2(0.0f, 0.0f);
            Vector2 textureUpperRight = new Vector2(1.0f, 0.0f);
            Vector2 textureLowerLeft = new Vector2(0.0f, 1.0f);
            Vector2 textureLowerRight = new Vector2(1.0f, 1.0f);

            for (int i = 0; i < Vertices.Length; i++)
            {
                Vertices[i].Normal = Normal;
            }

            Vertices[0].Position = LowerLeft;
            Vertices[0].TextureCoordinate = textureLowerLeft;
            Vertices[1].Position = UpperLeft;
            Vertices[1].TextureCoordinate = textureUpperLeft;
            Vertices[2].Position = LowerRight;
            Vertices[2].TextureCoordinate = textureLowerRight;
            Vertices[3].Position = UpperRight;
            Vertices[3].TextureCoordinate = textureUpperRight;

            Indexes[0] = 0;
            Indexes[1] = 1;
            Indexes[2] = 2;
            Indexes[3] = 2;
            Indexes[4] = 1;
            Indexes[5] = 3;
        }
    }
}