sneak/Shared/TreeScene.cs

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

namespace SemiColinGames {
  public sealed class TreeScene : IScene {

    const int MAX_SEGMENTS = 1000;
    const int MAX_VERTICES = MAX_SEGMENTS * 6;  // 2 triangles per segment

    private readonly Color backgroundColor = Color.SkyBlue;
    private readonly GraphicsDevice graphics;
    private readonly BasicEffect basicEffect;

    private VertexPositionColor[] vertices;
    private VertexBuffer vertexBuffer;

    public TreeScene(GraphicsDevice graphics) {
      this.graphics = graphics;

      basicEffect = new BasicEffect(graphics) {
        World = Matrix.CreateTranslation(0, 0, 0),
        View = Matrix.CreateLookAt(Vector3.Backward, Vector3.Zero, Vector3.Up),
        VertexColorEnabled = true,
        Projection = Matrix.CreateOrthographicOffCenter(-1920 / 2, 1920 / 2, -1080 / 4, 1080 * 3 / 4, -1, 1)
      };

      vertices = new VertexPositionColor[MAX_VERTICES];
      vertexBuffer = new VertexBuffer(
          graphics, typeof(VertexPositionColor), MAX_VERTICES, BufferUsage.WriteOnly);
    }

    ~TreeScene() {
      Dispose();
    }

    public void Dispose() {
      vertexBuffer.Dispose();
      GC.SuppressFinalize(this);
    }

    public struct Trapezoid {
      public Vector2 p1, p2, p3, p4;

      public void Rotate(float angle) {
        p1 = p1.Rotate(angle);
        p2 = p2.Rotate(angle);
        p3 = p3.Rotate(angle);
        p4 = p4.Rotate(angle);
      }

      public void Translate(Vector2 position) {
        p1 = Vector2.Add(p1, position);
        p2 = Vector2.Add(p2, position);
        p3 = Vector2.Add(p3, position);
        p4 = Vector2.Add(p4, position);
      }
    }

    public class TreeNode {
      public float Orientation;  // relative to parent
      public float Length;
      public float InWidth;
      public float OutWidth;
      public readonly List<TreeNode> Children;
      public Vector2 Position;

      public TreeNode(float orientation, float length, float inWidth, float outWidth) :
        this(orientation, length, inWidth, outWidth, new List<TreeNode>()) {
      }

      public TreeNode(float orientation, float length, float inWidth, float outWidth, TreeNode child) :
        this(orientation, length, inWidth, outWidth, new List<TreeNode>() { child }) {
      }

      public TreeNode(float orientation, float length, float inWidth, float outWidth, TreeNode child1, TreeNode child2) :
        this(orientation, length, inWidth, outWidth, new List<TreeNode>() { child1, child2 }) {
      }

      public TreeNode(float orientation, float length, float inWidth, float outWidth, TreeNode child1, TreeNode child2, TreeNode child3) :
        this(orientation, length, inWidth, outWidth, new List<TreeNode>() { child1, child2, child3 }) {
      }

      public TreeNode(float orientation, float length, float inWidth, float outWidth, List<TreeNode> children) {
        Orientation = orientation;
        Length = length;
        InWidth = inWidth;
        OutWidth = outWidth;
        Children = children;
        Position = Vector2.Zero;
      }
    }

    public void Draw(bool isRunningSlowly, IWorld iworld, bool paused) {
      var tree =
        new TreeNode(-0.2f, 100, 10, 6,
          new TreeNode(-0.2f, 100, 10, 6,
            new TreeNode(-0.2f, 100, 10, 6,
              new TreeNode(-0.3f, 100, 6, 4,
                new TreeNode(-0.1f, 100, 6, 4,
                  new TreeNode(-0.3f, 150, 4, 2),
                  new TreeNode(0.2f, 200, 4, 2),
                  new TreeNode(0.5f, 100, 4, 2))),
              new TreeNode(0.5f, 100, 6, 4,
                new TreeNode(-0.1f, 100, 6, 4,
                  new TreeNode(-0.1f, 150, 4, 2),
                  new TreeNode(0.2f, 200, 4, 2))))));

      graphics.Clear(backgroundColor);

      var segments = new List<Trapezoid>();

      LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
      queue.AddLast(tree);
      while (queue.Count > 0) {
        TreeNode parent = queue.First.Value;
        queue.RemoveFirst();
        Vector2 outVector = new Vector2(0, parent.Length).Rotate(parent.Orientation);
        Vector2 outPosition = Vector2.Add(parent.Position, outVector);

        // We want a trapezoid with 4 points. A is the in position, B is the out position.
        // The TreeNode.Length is the distance from A to B.
        //
        // We come up with the points relative to A being the origin, then rotate the trapezoid
        // by its orientation, and translate the result to A's actual position.
        //
        //     3---B---4     <-- length = outWidth
        //    /    |    \
        //   /     |     \
        //  1------A------2  <-- length = inWidth

        // This fudge factor lengthens the sides a bit longer to prevent small discontinuities
        // in the rendered result.
        // TODO: remove this sideLengthFudge.
        float sideLengthFudge = 1.05f;
        Trapezoid t = new Trapezoid();
        t.p1 = new Vector2(-parent.InWidth, 0);
        t.p2 = new Vector2(parent.InWidth, 0);
        t.p3 = new Vector2(-parent.OutWidth, parent.Length * sideLengthFudge);
        t.p4 = new Vector2(parent.OutWidth, parent.Length * sideLengthFudge);
        t.Rotate(parent.Orientation);
        t.Translate(parent.Position);

        segments.Add(t);
        foreach (TreeNode child in parent.Children) {
          child.Position = outPosition;
          child.Orientation += parent.Orientation;
          queue.AddLast(child);
        }
      }

      Color color = Color.SaddleBrown;
      for (int i = 0; i < segments.Count; i++) {
        Trapezoid t = segments[i];
        vertices[i * 6] = new VertexPositionColor(new Vector3(t.p1.X, t.p1.Y, 0), color);
        vertices[i * 6 + 1] = new VertexPositionColor(new Vector3(t.p2.X, t.p2.Y, 0), color);
        vertices[i * 6 + 2] = new VertexPositionColor(new Vector3(t.p3.X, t.p3.Y, 0), color);
        vertices[i * 6 + 3] = new VertexPositionColor(new Vector3(t.p2.X, t.p2.Y, 0), color);
        vertices[i * 6 + 4] = new VertexPositionColor(new Vector3(t.p3.X, t.p3.Y, 0), color);
        vertices[i * 6 + 5] = new VertexPositionColor(new Vector3(t.p4.X, t.p4.Y, 0), color);
      }

      graphics.SetVertexBuffer(vertexBuffer);
      vertexBuffer.SetData(vertices);

      foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes) {
        pass.Apply();
        graphics.DrawPrimitives(PrimitiveType.TriangleList, 0, segments.Count * 2);
      }
    }
  }
}