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 Draw(bool isRunningSlowly, IWorld iworld, bool paused) {
      var skeleton = new List<Vector2> {
        new Vector2(0, 0),
        new Vector2(0, 100),
        new Vector2(10, 200),
        new Vector2(30, 300),
        new Vector2(60, 400),
        new Vector2(100, 500),
      };

      graphics.Clear(backgroundColor);

      var segments = new List<Trapezoid>();

      for (int i = 0; i < skeleton.Count - 1; i++) {
        Vector2 low = skeleton[i];
        Vector2 high = skeleton[i + 1];
        Trapezoid t;
        int width = 10 - i;
        t.p1 = new Vector2(low.X - width, low.Y);
        t.p2 = new Vector2(low.X + width, low.Y);
        t.p3 = new Vector2(high.X - width + 4, high.Y);
        t.p4 = new Vector2(high.X + width - 4, high.Y);
        segments.Add(t);
      }

      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);
      }
    }
  }
}