recrownedathenaeum/RecrownedAthenaeum/Render/RectangleRenderer.cs

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

namespace RecrownedAthenaeum.Render
{
    /// <summary>
    /// Renders rectangles using the <see cref="PrimitiveBatch"/>.
    /// </summary>
    public class RectangleRenderer
    {
        /// <summary>
        /// The <see cref="PrimitiveBatch"/> used. Needs to be disposed.
        /// </summary>
        public readonly PrimitiveBatch primitiveBatch;
        private bool began;
        private bool filling;

        /// <summary>
        /// Creates a rectangle renderer with the given <see cref="PrimitiveBatch"/>.
        /// </summary>
        /// <param name="primitiveBatch"></param>
        public RectangleRenderer(PrimitiveBatch primitiveBatch)
        {
            this.primitiveBatch = primitiveBatch;
        }

        /// <summary>
        /// Begins the render batch.
        /// </summary>
        /// <param name="filled">Whether or not to fill the rectangle.</param>
        public void Begin(bool filled)
        {
            filling = filled;
            if (began) throw new InvalidOperationException("Cannot begin twice.");
            primitiveBatch.Begin(filled ? PrimitiveType.TriangleStrip : PrimitiveType.LineStrip);
            began = true;
        }

        /// <summary>
        /// Ends the batch.
        /// </summary>
        public void End()
        {
            if (!began) throw new InvalidOperationException("Cannot end before beginning.");
            primitiveBatch.End();
            began = false;
        }


        /// <summary>
        /// Draws a basic rectangle given bottom left and top right.
        /// </summary>
        /// <param name="x">X coordinate of bottom left.</param>
        /// <param name="y">Y coordinate of bottom left.</param>
        /// <param name="width">Width of rectangle.</param>
        /// <param name="height">Height of rectangle.</param>
        /// <param name="color">Color of all vertices of this rectangle.</param>
        /// <param name="rotation">Rotation of rectangle. Default is 0 radians.</param>
        public void DrawRectangle(int x, int y, int width, int height, Color color, double rotation = 0)
        {
            if (!began) throw new InvalidOperationException("Renderer must be started by calling Begin.");
            Vector2[] corners = new Vector2[4];

            corners[0] = new Vector2(x, y);
            corners[1] = new Vector2(x + (float)Math.Cos(rotation) * width, y + (float)Math.Sin(rotation) * width);
            double topRightAngleFromOrig = Math.Atan(height / (double)width);
            float origDiagonalHypotenuse = (float)Math.Sqrt(width * width * height * height);
            corners[2] = new Vector2(x + (float)Math.Cos(topRightAngleFromOrig + rotation) * origDiagonalHypotenuse, y + (float)Math.Sin(topRightAngleFromOrig + rotation) * origDiagonalHypotenuse);
            corners[3] = new Vector2(x + (float)Math.Cos(rotation + Math.PI / 4f) * height, y + (float)Math.Sin(rotation) * height);

            if (filling)
            {
                primitiveBatch.AddVertex(corners[1], color);
                primitiveBatch.AddVertex(corners[2], color);
                primitiveBatch.AddVertex(corners[0], color);
                primitiveBatch.AddVertex(corners[3], color);
            } else
            {
                primitiveBatch.AddVertex(corners[0], color);
                primitiveBatch.AddVertex(corners[1], color);
                primitiveBatch.AddVertex(corners[2], color);
                primitiveBatch.AddVertex(corners[3], color);
            }
        }
    }
}