WIP: More sprite stuff!

* Added a public Rectangle struct.
    * Added a constructor for the Point struct to slightly reduce typing fatigue. :)
    * Modified the way that Canvas classes are initialized so that
      sprite sheets and scrolling backgrounds will be possible to
      implement.

DotSDL/Graphics/Canvas.cs

@@ -1,31 +1,70 @@
-namespace DotSDL.Graphics {
+using System;
+
+namespace DotSDL.Graphics {
     /// <summary>
     /// A representation of the contents of the SDL window, with a number of
     /// helper routines.
     /// </summary>
     public class Canvas {
+        private int _width, _height;
+
         /// <summary>
         /// The raw pixels in the <see cref="Canvas"/>.
         /// </summary>
         public Color[] Pixels;
 
         /// <summary>
-        /// Gets the width of the <see cref="Canvas"/>.
+        /// Gets or sets the width of the <see cref="Canvas"/> texture.
         /// </summary>
-        public int Width { get; private set; }
+        public int Width {
+            get => _width;
+            set {
+                if(value <= 0) throw new ArgumentException("Width must be greater than 0.");
+
+                _width = value;
+                Resize();
+            }
+        }
 
         /// <summary>
-        /// Gets the height of the <see cref="Canvas"/>.
+        /// Gets or sets the height of the <see cref="Canvas"/> texture.
         /// </summary>
-        public int Height { get; private set; }
+        public int Height {
+            get => _height;
+            set {
+                if(value <= 0) throw new ArgumentException("Height must be greater than 0.");
+
+                _height = value;
+                Resize();
+            }
+        }
 
         /// <summary>
-        /// Initialization a new <see cref="Canvas"/>.
+        /// Sets the section of the <see cref="Canvas"/> that should be drawn. If the size values are set to 0, the
+        /// <see cref="Canvas"/> will fill as much of its containing object as possible.
         /// </summary>
-        /// <param name="width">The width of the <see cref="Canvas"/>.</param>
-        /// <param name="height">The height of the <see cref="Canvas"/>.</param>
-        internal Canvas(int width, int height) {
-            SetSize(width, height);
+        public Rectangle Clipping { get; set; }
+
+        /// <summary>
+        /// Initializes a new <see cref="Canvas"/>.
+        /// </summary>
+        /// <param name="textureWidth">The width of the <see cref="Canvas"/>.</param>
+        /// <param name="textureHeight">The height of the <see cref="Canvas"/>.</param>
+        internal Canvas(int textureWidth, int textureHeight) : this(textureWidth, textureHeight, new Rectangle(0, 0, textureWidth, textureHeight)) { }
+
+        /// <summary>
+        /// Initializes a new <see cref="Canvas"/>.
+        /// </summary>
+        /// <param name="textureWidth">The width of the <see cref="Canvas"/>.</param>
+        /// <param name="textureHeight">The height of the <see cref="Canvas"/>.</param>
+        /// <param name="clipping">The clipping <see cref="Rectangle"/> for the <see cref="Canvas"/>.</param>
+        internal Canvas(int textureWidth, int textureHeight, Rectangle clipping) {
+            _width = textureWidth;
+            _height = textureHeight;
+
+            Clipping = clipping;
+
+            Resize();
         }
 
         /// <summary>
@@ -51,12 +90,7 @@
         /// Resizes the <see cref="Canvas"/>. Please note that this will also clear the canvas of
         /// its existing contents.
         /// </summary>
-        /// <param name="width">The new width of the <see cref="Canvas"/>.</param>
-        /// <param name="height">The new height of the <see cref="Canvas"/>.</param>
-        internal void SetSize(int width, int height) {
-            Width = width;
-            Height = height;
-
+        protected void Resize() {
             Pixels = new Color[Width * Height];
         }
     }

DotSDL/Graphics/Point.cs

@@ -2,7 +2,7 @@
     /// <summary>
     /// Represents a point in 2D space.
     /// </summary>
-    public class Point {
+    public struct Point {
         /// <summary>
         /// The X coordinate of the point.
         /// </summary>
@@ -12,5 +12,15 @@
         /// The Y coordinate of the point.
         /// </summary>
         public int Y { get; set; }
+
+        /// <summary>
+        /// Creates a new <see cref="Point"/>.
+        /// </summary>
+        /// <param name="x">The X value of the new <see cref="Point"/>.</param>
+        /// <param name="y">The Y value of the new <see cref="Point"/>.</param>
+        public Point(int x, int y) {
+            X = x;
+            Y = y;
+        }
     }
 }

DotSDL/Graphics/Rectangle.cs

@@ -0,0 +1,35 @@
+namespace DotSDL.Graphics {
+    /// <summary>
+    /// Represents a rectangle in 2D space.
+    /// </summary>
+    public struct Rectangle {
+        /// <summary>
+        /// A <see cref="Point"/> representing the position of the <see cref="Rectangle"/>.
+        /// </summary>
+        public Point Position { get; set; }
+        
+        /// <summary>
+        /// A <see cref="Point"/> representing the size of the <see cref="Rectangle"/>.
+        /// </summary>
+        public Point Size { get; set; }
+
+        /// <summary>
+        /// Creates a new <see cref="Rectangle"/>.
+        /// </summary>
+        /// <param name="position">A <see cref="Point"/> representing the position of the new <see cref="Rectangle"/>.</param>
+        /// <param name="size">A <see cref="Point"/> representing the size of the new <see cref="Rectangle"/>.</param>
+        public Rectangle(Point position, Point size) {
+            Position = position;
+            Size = size;
+        }
+        
+        /// <summary>
+        /// Creates a new <see cref="Rectangle"/>.
+        /// </summary>
+        /// <param name="x">The X position of the new <see cref="Rectangle"/>.</param>
+        /// <param name="y">The Y position of the new <see cref="Rectangle"/>.</param>
+        /// <param name="width">The width of the new <see cref="Rectangle"/>.</param>
+        /// <param name="height">The height of the new <see cref="Rectangle"/>.</param>
+        public Rectangle(int x, int y, int width, int height) : this(new Point(x, y), new Point(width, height)) { }
+    }
+}

DotSDL/Graphics/SdlWindow.cs

@@ -175,6 +175,14 @@ namespace DotSDL.Graphics {
             IsDestroyed = true;
         }
 
+        /// <summary>
+        /// Plots the sprites stored in <see cref="Sprites"/> to the screen. Please note that this method is called by
+        /// DotSDL's drawing routines and does not need to be called manually. You usually do not need to override this
+        /// method.
+        /// </summary>
+        public virtual void DrawSprites() {
+        }
+
         /// <summary>
         /// Gets an <see cref="IntPtr"/> that points to what should be displayed on the window's background. You usually
         /// do not need to override this method.

DotSDL/Graphics/Sprite.cs

@@ -5,9 +5,25 @@ namespace DotSDL.Graphics {
     /// Represents a graphical, two-dimensional object in a program.
     /// </summary>
     public class Sprite : Canvas {
+        /// <summary>
+        /// The position on the screen where the <see cref="Sprite"/> should be drawn.
+        /// </summary>
         public Vector2 Position { get; set; }
+
+        /// <summary>
+        /// The scale of the <see cref="Sprite"/>. 1.0f is 100%.
+        /// </summary>
         public Vector2 Scale { get; set; }
+
+        /// <summary>
+        /// The order in which the sprite is drawn. Lower numbered <see cref="Sprite"/> instances are drawn first
+        /// and will appear on the bottom.
+        /// </summary>
         public int ZOrder { get; set; }
+
+        /// <summary>
+        /// <c>true</c> if the sprite should be drawn to the screen, otherwise <c>false</c>.
+        /// </summary>
         public bool Shown { get; set; }
 
         /// <summary>
@@ -63,8 +79,6 @@ namespace DotSDL.Graphics {
         /// <param name="zorder">A value indicating the order in which this <see cref="Sprite"/> is drawn. Higher numbered
         /// sprites are drawn on top of other sprites and, thus, will appear above them.</param>
         public Sprite(int width, int height, Vector2 position, Vector2 scale, int zorder) : base(width, height) {
-            SetSize(width, height);
-
             Position = position;
             Scale    = scale;
             ZOrder   = zorder;