Add canvas and image support

Adds support for drawing "pixels" and displaying
images in the terminal.

src/Spectre.Console.ImageSharp/CanvasImageExtensions.cs

@@ -0,0 +1,135 @@
+using System;
+using SixLabors.ImageSharp.Processing;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="CanvasImage"/>.
+    /// </summary>
+    public static class CanvasImageExtensions
+    {
+        /// <summary>
+        /// Sets the maximum width of the rendered image.
+        /// </summary>
+        /// <param name="image">The canvas image.</param>
+        /// <param name="maxWidth">The maximum width.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static CanvasImage MaxWidth(this CanvasImage image, int? maxWidth)
+        {
+            if (image is null)
+            {
+                throw new ArgumentNullException(nameof(image));
+            }
+
+            image.MaxWidth = maxWidth;
+            return image;
+        }
+
+        /// <summary>
+        /// Disables the maximum width of the rendered image.
+        /// </summary>
+        /// <param name="image">The canvas image.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static CanvasImage NoMaxWidth(this CanvasImage image)
+        {
+            if (image is null)
+            {
+                throw new ArgumentNullException(nameof(image));
+            }
+
+            image.MaxWidth = null;
+            return image;
+        }
+
+        /// <summary>
+        /// Sets the pixel width.
+        /// </summary>
+        /// <param name="image">The canvas image.</param>
+        /// <param name="width">The pixel width.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static CanvasImage PixelWidth(this CanvasImage image, int width)
+        {
+            if (image is null)
+            {
+                throw new ArgumentNullException(nameof(image));
+            }
+
+            image.PixelWidth = width;
+            return image;
+        }
+
+        /// <summary>
+        /// Mutates the underlying image.
+        /// </summary>
+        /// <param name="image">The canvas image.</param>
+        /// <param name="action">The action that mutates the underlying image.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static CanvasImage Mutate(this CanvasImage image, Action<IImageProcessingContext> action)
+        {
+            if (image is null)
+            {
+                throw new ArgumentNullException(nameof(image));
+            }
+
+            if (action is null)
+            {
+                throw new ArgumentNullException(nameof(action));
+            }
+
+            image.Image.Mutate(action);
+            return image;
+        }
+
+        /// <summary>
+        /// Uses a bicubic sampler that implements the bicubic kernel algorithm W(x).
+        /// </summary>
+        /// <param name="image">The canvas image.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static CanvasImage BicubicResampler(this CanvasImage image)
+        {
+            if (image is null)
+            {
+                throw new ArgumentNullException(nameof(image));
+            }
+
+            image.Resampler = KnownResamplers.Bicubic;
+            return image;
+        }
+
+        /// <summary>
+        /// Uses a bilinear sampler. This interpolation algorithm
+        /// can be used where perfect image transformation with pixel matching is impossible,
+        /// so that one can calculate and assign appropriate intensity values to pixels.
+        /// </summary>
+        /// <param name="image">The canvas image.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static CanvasImage BilinearResampler(this CanvasImage image)
+        {
+            if (image is null)
+            {
+                throw new ArgumentNullException(nameof(image));
+            }
+
+            image.Resampler = KnownResamplers.Triangle;
+            return image;
+        }
+
+        /// <summary>
+        /// Uses a Nearest-Neighbour sampler that implements the nearest neighbor algorithm.
+        /// This uses a very fast, unscaled filter which will select the closest pixel to
+        /// the new pixels position.
+        /// </summary>
+        /// <param name="image">The canvas image.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static CanvasImage NearestNeighborResampler(this CanvasImage image)
+        {
+            if (image is null)
+            {
+                throw new ArgumentNullException(nameof(image));
+            }
+
+            image.Resampler = KnownResamplers.NearestNeighbor;
+            return image;
+        }
+    }
+}