Add Image and ImageFrame constructors that take a clear color as parameter.

This is good for performance because this avoids first needing to clear the buffer with zeroes.

src/ImageSharp/ImageFrameCollection.cs

@@ -23,7 +23,14 @@ namespace SixLabors.ImageSharp
             this.parent = parent;
 
             // Frames are already cloned within the caller
-            this.frames.Add(new ImageFrame<TPixel>(parent.GetConfiguration().MemoryManager, width, height));
+            if (parent.ClearColor.HasValue)
+            {
+                this.frames.Add(new ImageFrame<TPixel>(parent.GetConfiguration(), width, height, parent.ClearColor.Value));
+            }
+            else
+            {
+                this.frames.Add(new ImageFrame<TPixel>(parent.GetConfiguration().MemoryManager, width, height));
+            }
         }
 
         internal ImageFrameCollection(Image<TPixel> parent, IEnumerable<ImageFrame<TPixel>> frames)
@@ -143,7 +150,16 @@ namespace SixLabors.ImageSharp
         /// <inheritdoc/>
         public ImageFrame<TPixel> CreateFrame()
         {
-            var frame = new ImageFrame<TPixel>(this.parent.GetConfiguration().MemoryManager, this.RootFrame.Width, this.RootFrame.Height);
+            ImageFrame<TPixel> frame;
+            if (this.parent.ClearColor.HasValue)
+            {
+                frame = new ImageFrame<TPixel>(this.parent.GetConfiguration(), this.RootFrame.Width, this.RootFrame.Height, this.parent.ClearColor.Value);
+            }
+            else
+            {
+                frame = new ImageFrame<TPixel>(this.parent.GetConfiguration().MemoryManager, this.RootFrame.Width, this.RootFrame.Height);
+            }
+
             this.frames.Add(frame);
             return frame;
         }

src/ImageSharp/Image{TPixel}.cs

@@ -22,6 +22,7 @@ namespace SixLabors.ImageSharp
     {
         private readonly Configuration configuration;
         private readonly ImageFrameCollection<TPixel> frames;
+        private readonly TPixel? clearColor;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Image{TPixel}"/> class
@@ -37,6 +38,21 @@ namespace SixLabors.ImageSharp
         {
         }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Image{TPixel}"/> class
+        /// with the height and the width of the image.
+        /// </summary>
+        /// <param name="configuration">
+        /// The configuration providing initialization code which allows extending the library.
+        /// </param>
+        /// <param name="width">The width of the image in pixels.</param>
+        /// <param name="height">The height of the image in pixels.</param>
+        /// <param name="clearColor">The color to initialize the pixels with.</param>
+        public Image(Configuration configuration, int width, int height, TPixel clearColor)
+            : this(configuration, width, height, clearColor, new ImageMetaData())
+        {
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Image{TPixel}"/> class
         /// with the height and the width of the image.
@@ -66,6 +82,25 @@ namespace SixLabors.ImageSharp
             this.frames = new ImageFrameCollection<TPixel>(this, width, height);
         }
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Image{TPixel}"/> class
+        /// with the height and the width of the image.
+        /// </summary>
+        /// <param name="configuration">
+        /// The configuration providing initialization code which allows extending the library.
+        /// </param>
+        /// <param name="width">The width of the image in pixels.</param>
+        /// <param name="height">The height of the image in pixels.</param>
+        /// <param name="clearColor">The clear color.</param>
+        /// <param name="metadata">The images metadata.</param>
+        internal Image(Configuration configuration, int width, int height, TPixel clearColor, ImageMetaData metadata) {
+            this.configuration = configuration ?? Configuration.Default;
+            this.PixelType = new PixelTypeInfo(Unsafe.SizeOf<TPixel>() * 8);
+            this.MetaData = metadata ?? new ImageMetaData();
+            this.clearColor = clearColor;
+            this.frames = new ImageFrameCollection<TPixel>(this, width, height);
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Image{TPixel}" /> class
         /// with the height and the width of the image.
@@ -104,6 +139,11 @@ namespace SixLabors.ImageSharp
         /// </summary>
         public IImageFrameCollection<TPixel> Frames => this.frames;
 
+        /// <summary>
+        /// Gets the clear color to initialize the image frame pixels with.
+        /// </summary>
+        internal TPixel? ClearColor => this.clearColor;
+
         /// <summary>
         /// Gets the root frame.
         /// </summary>

src/ImageSharp/Memory/BufferExtensions.cs

@@ -52,6 +52,18 @@ namespace SixLabors.ImageSharp.Memory
             buffer.Span.Clear();
         }
 
+        /// <summary>
+        /// Fills the contents of this buffer.
+        /// </summary>
+        /// <param name="buffer">The buffer</param>
+        /// <param name="value">The value to fill the buffer with.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void Fill<T>(this IBuffer<T> buffer, T value)
+            where T : struct
+        {
+            buffer.Span.Fill(value);
+        }
+
         public static ref T DangerousGetPinnableReference<T>(this IBuffer<T> buffer)
             where T : struct =>
             ref MemoryMarshal.GetReference(buffer.Span);