Added some basic collision properties to sprites.

* Moved both the Shown and ZOrder properties to the Canvas class.
    * Sprites and Backgrounds are now both considered when doing z-order
      checks. As such, sprites can now be drawn under backgrounds. This will
      likely need more optimization.

DotSDL/Graphics/Background.cs

@@ -30,7 +30,7 @@ namespace DotSDL.Graphics {
             // TODO: Might be able to make this faster by leveraging memcpy(). Need to benchmark it.
             unsafe {
                 var copySize = Width * Height * 4;  // Width x Height at 4 bytes per pixel.
-                Render.LockTexture(Texture, IntPtr.Zero, out var pixels, out var _);
+                Render.LockTexture(Texture, IntPtr.Zero, out var pixels, out _);
                 Buffer.MemoryCopy(GetCanvasPointer().ToPointer(), pixels, copySize, copySize);
                 Render.UnlockTexture(Texture);
             }

DotSDL/Graphics/Canvas.cs

@@ -153,6 +153,17 @@ namespace DotSDL.Graphics {
             }
         }
 
+        /// <summary>
+        /// <c>true</c> if the <see cref="Canvas"/> should be drawn to the screen, otherwise <c>false</c>.
+        /// </summary>
+        public bool Shown { get; set; } = true;
+
+        /// <summary>
+        /// The order in which the canvas is drawn. Lower numbered <see cref="Canvas"/> instances are drawn first
+        /// and will appear on the bottom. This number can be negative.
+        /// </summary>
+        public int ZOrder { get; set; }
+
         /// <summary>
         /// 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.

DotSDL/Graphics/SdlWindow.cs

@@ -24,6 +24,8 @@ namespace DotSDL.Graphics {
         private uint _nextVideoUpdate;
         private uint _nextGameUpdate;
 
+        private List<Canvas> _drawList = new List<Canvas>();
+
         private ScalingQuality _scalingQuality = ScalingQuality.Nearest;
 
         /// <summary>Gets the background layer of this window. This is equivalent to accessing Layers[0].</summary>
@@ -191,6 +193,7 @@ namespace DotSDL.Graphics {
                     BlendMode = BlendMode.None
                 }
             };
+            Background.ZOrder = int.MinValue;
             Background.CreateTexture();
 
             CameraView = new Rectangle(
@@ -240,20 +243,29 @@ namespace DotSDL.Graphics {
 
             Render.SetRenderTarget(_renderer, _texture);
 
-            // Blit the background canvases to the target texture.
-            foreach(var canvas in Layers) {
-                canvas.Clipping.Position = CameraView.Position;
-                canvas.Clipping.Size = CameraView.Size;
-                canvas.UpdateTexture();
-                unsafe {
-                    var canvasClippingRect = canvas.Clipping.SdlRect;
-                    Render.RenderCopy(_renderer, canvas.Texture, new IntPtr(&canvasClippingRect), IntPtr.Zero);
+            // Sort all of the canvases, then draw them.
+            _drawList.Clear();
+            _drawList.AddRange(Layers.Where(l => l.Shown).ToArray());
+            _drawList.AddRange(Sprites.Where(s => s.Shown).ToArray());
+
+            foreach(var canvas in _drawList.OrderBy(layer => layer.ZOrder)) {
+                switch(canvas) {
+                    case Sprite sprite:
+                        DrawSprite(sprite);
+                        break;
+                    default:
+                        canvas.Clipping.Position = CameraView.Position;
+                        canvas.Clipping.Size = CameraView.Size;
+                        canvas.UpdateTexture();
+                        unsafe {
+                            var canvasClippingRect = canvas.Clipping.SdlRect;
+                            Render.RenderCopy(_renderer, canvas.Texture, new IntPtr(&canvasClippingRect), IntPtr.Zero);
+                        }
+
+                        break;
                 }
             }
 
-            // Plot sprites on top of the background layer.
-            if(Sprites.Count > 0) DrawSprites();
-
             Render.SetRenderTarget(_renderer, IntPtr.Zero);
             Render.RenderCopy(_renderer, _texture, IntPtr.Zero, IntPtr.Zero);
 
@@ -306,61 +318,58 @@ namespace DotSDL.Graphics {
         }
 
         /// <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. Additionally, this method will not be
-        /// called if there are no sprites defined. You usually do not need to override this method.
-        /// </summary>
-        public virtual void DrawSprites() {
-            Render.SetRenderTarget(_renderer, _texture);
-            foreach(var sprite in Sprites.Where(e => e.Shown).OrderBy(e => e.ZOrder)) {
-                var srcRect = sprite.Clipping.SdlRect;
-                var drawSize = sprite.DrawSize;
-
-                Rectangle dest;
-                Point rotationCenter;
-                if(sprite.CoordinateSystem == CoordinateSystem.ScreenSpace) {
-                    dest = new Rectangle(sprite.Position, drawSize);
-                    rotationCenter = sprite.RotationCenter;
-                } else {
-                    // Create a set of world coordinates based on the position of the camera
-                    // and this sprite.
-                    var relPosition = new Point(sprite.Position - CameraView.Position);
-                    var screenPosition = new Point(
-                        (int)((float)relPosition.X / CameraView.Size.X * RenderWidth),
-                        (int)((float)relPosition.Y / CameraView.Size.Y * RenderHeight)
-                    );
-                    var scaleFactorX = (float)RenderWidth / CameraView.Size.X;
-                    var scaleFactorY = (float)RenderHeight / CameraView.Size.Y;
-                    var size = new Point(
-                        (int)(drawSize.X * scaleFactorX),
-                        (int)(drawSize.Y * scaleFactorY)
-                    );
-
-                    dest = new Rectangle(screenPosition, size);
-                    rotationCenter = new Point(
-                        (int)(sprite.RotationCenter.X * scaleFactorX),
-                        (int)(sprite.RotationCenter.Y * scaleFactorY)
-                    );
-                }
+        /// Plots a sprite to the screen. Please note that this method is called by DotSDL's drawing
+        /// routines and does not need to be called manually. Additionally, this method will never be
+        /// called if there are no active sprites. You usually do not need to override this method.
+        /// </summary>
+        public virtual void DrawSprite(Sprite sprite) {
+            var srcRect = sprite.Clipping.SdlRect;
+            var drawSize = sprite.DrawSize;
+
+            Rectangle dest;
+            Point rotationCenter;
+            if(sprite.CoordinateSystem == CoordinateSystem.ScreenSpace) {
+                dest = new Rectangle(sprite.Position, drawSize);
+                rotationCenter = sprite.RotationCenter;
+            } else {
+                // Create a set of world coordinates based on the position of the camera
+                // and this sprite.
+                var relPosition = new Point(sprite.Position - CameraView.Position);
+                var screenPosition = new Point(
+                    (int)((float)relPosition.X / CameraView.Size.X * RenderWidth),
+                    (int)((float)relPosition.Y / CameraView.Size.Y * RenderHeight)
+                );
+                var scaleFactorX = (float)RenderWidth / CameraView.Size.X;
+                var scaleFactorY = (float)RenderHeight / CameraView.Size.Y;
+                var size = new Point(
+                    (int)(drawSize.X * scaleFactorX),
+                    (int)(drawSize.Y * scaleFactorY)
+                );
+
+                dest = new Rectangle(screenPosition, size);
+                rotationCenter = new Point(
+                    (int)(sprite.RotationCenter.X * scaleFactorX),
+                    (int)(sprite.RotationCenter.Y * scaleFactorY)
+                );
+            }
 
-                var destRect = dest.SdlRect;
-                var rotationCenterPoint = rotationCenter.SdlPoint;
-
-                unsafe {
-                    var srcRectPtr = new IntPtr(&srcRect);
-                    var destRectPtr = new IntPtr(&destRect);
-                    var rotationCenterPtr = new IntPtr(&rotationCenterPoint);
-
-                    Render.RenderCopyEx(
-                        renderer: _renderer,
-                        texture: sprite.Texture,
-                        srcRect: srcRectPtr,
-                        dstRect: destRectPtr,
-                        angle: sprite.Rotation,
-                        center: rotationCenterPtr,
-                        flip: sprite.Flip
-                    );
-                }
+            var destRect = dest.SdlRect;
+            var rotationCenterPoint = rotationCenter.SdlPoint;
+
+            unsafe {
+                var srcRectPtr = new IntPtr(&srcRect);
+                var destRectPtr = new IntPtr(&destRect);
+                var rotationCenterPtr = new IntPtr(&rotationCenterPoint);
+
+                Render.RenderCopyEx(
+                    renderer: _renderer,
+                    texture: sprite.Texture,
+                    srcRect: srcRectPtr,
+                    dstRect: destRectPtr,
+                    angle: sprite.Rotation,
+                    center: rotationCenterPtr,
+                    flip: sprite.Flip
+                );
             }
         }
 
@@ -486,17 +495,13 @@ namespace DotSDL.Graphics {
         /// <summary>
         /// Displays the window and begins executing code that's associated with it.
         /// </summary>
-        public void Start() {
-            Start(0, 0);
-        }
+        public void Start() => Start(0, 0);
 
         /// <summary>
         /// Displays the window and begins executing code that's associated with it.
         /// </summary>
         /// <param name="updateRate">The desired number of milliseconds between frames and game logic updates. 0 causes the display and game to be continuously updated.</param>
-        public void Start(uint updateRate) {
-            Start(updateRate, updateRate);
-        }
+        public void Start(uint updateRate) => Start(updateRate, updateRate);
 
         /// <summary>
         /// Displays the window and begins executing code that's associated with it.

DotSDL/Graphics/Sprite.cs

@@ -9,6 +9,8 @@ namespace DotSDL.Graphics {
     public class Sprite : Canvas {
         private readonly Point _effectiveSize = new Point();
         private Vector2<float> _scale;
+        private bool _collisionBoxSet;
+        private Rectangle _collisionBox;
 
         /// <summary>
         /// The position on the screen where the <see cref="Sprite"/> should be drawn.
@@ -41,6 +43,9 @@ namespace DotSDL.Graphics {
                 _scale = value;
                 _effectiveSize.X = (int)(Width * _scale.X);
                 _effectiveSize.Y = (int)(Height * _scale.Y);
+
+                if(!_collisionBoxSet)
+                    _collisionBox = new Rectangle(new Point(0, 0), _effectiveSize);
             }
         }
 
@@ -84,15 +89,20 @@ namespace DotSDL.Graphics {
         public CoordinateSystem CoordinateSystem { get; set; } = CoordinateSystem.WorldSpace;
 
         /// <summary>
-        /// <c>true</c> if the sprite should be drawn to the screen, otherwise <c>false</c>.
+        /// Gets or sets the size and position of the collision box for this <see cref="Sprite"/>.
         /// </summary>
-        public bool Shown { get; set; }
+        public Rectangle CollisionBox {
+            get => _collisionBox;
+            set {
+                _collisionBox = value;
+                _collisionBoxSet = true;
+            }
+        }
 
         /// <summary>
-        /// The order in which the sprite is drawn. Lower numbered <see cref="Sprite"/> instances are drawn first
-        /// and will appear on the bottom.
+        /// Gets or sets whether or not collision calculations are performed on this <see cref="Sprite"/>.
         /// </summary>
-        public int ZOrder { get; set; }
+        public bool HasCollision { get; set; }
 
         /// <summary>
         /// Initializes a new <see cref="Sprite"/>.
@@ -174,6 +184,35 @@ namespace DotSDL.Graphics {
             (int)(Clipping.Size.Y * _scale.Y / 2)
         );
 
+        /// <summary>
+        /// Determines whether or not a given point collides with this <see cref="Sprite"/>. By default
+        /// this will test the point against the sprite's <see cref="CollisionBox"/>, but this method
+        /// can be overridden.
+        /// </summary>
+        /// <param name="point">The <see cref="Point"/> to check.</param>
+        /// <returns><c>true</c> if this object's collision is enabled and this sprite's collision
+        /// routine determines that the given pixel collides with the sprite, otherwise <c>false</c>.</returns>
+        public virtual bool CheckCollision(Point point) {
+            if(!HasCollision) return false;
+
+            return point.X >= CollisionBox.Position.X + Position.X
+                && point.X <= CollisionBox.Position.X + CollisionBox.Size.X + Position.X
+                && point.Y >= CollisionBox.Position.Y + Position.Y
+                && point.Y <= CollisionBox.Position.Y + CollisionBox.Size.Y + Position.Y;
+        }
+
+        /// <summary>
+        /// Determines whether or not a given point collides with this <see cref="Sprite"/>. By default
+        /// this will test the point against the sprite's <see cref="CollisionBox"/>. If you wish to
+        /// override this sprite's collision routine, override the <see cref="CheckCollision(DotSDL.Graphics.Point)"/>
+        /// method instead.
+        /// </summary>
+        /// <param name="x">The X coordinate of the point to check.</param>
+        /// <param name="y">The Y coordinate of the point to check.</param>
+        /// <returns><c>true</c> if this object's collision is enabled and this sprite's collision
+        /// routine determines that the given pixel collides with the sprite, otherwise <c>false</c>.</returns>
+        public bool CheckCollision(int x, int y) => CheckCollision(new Point(x, y));
+
         /// <inheritdoc/>
         internal override void CreateTexture() {
             CreateTexture(Render.TextureAccess.Static);
@@ -184,7 +223,8 @@ namespace DotSDL.Graphics {
         /// <see cref="Canvas.Pixels"/> array is changed after adding this sprite to the sprite list associated
         /// with the application's <see cref="SdlWindow"/>.
         /// </summary>
-        /// <returns><c>true</c> if the texture was successfully updated, otherwise <c>false</c>. This will return <c>false</c> if this <see cref="Sprite"/> hasn't been added to the sprite list.</returns>
+        /// <returns><c>true</c> if the texture was successfully updated, otherwise <c>false</c>. This will return
+        /// <c>false</c> if this <see cref="Sprite"/> hasn't been added to the sprite list.</returns>
         public new bool UpdateTexture() {
             return base.UpdateTexture();
         }