Add smart animated format conversion.

src/ImageSharp/Common/Helpers/SimdUtils.HwIntrinsics.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics;
@@ -656,6 +657,36 @@ public static Vector128<byte> BlendVariable(Vector128<byte> left, Vector128<byte
             return AdvSimd.BitwiseSelect(signedMask, right.AsInt16(), left.AsInt16()).AsByte();
         }
 
+        /// <summary>
+        /// Blend packed 32-bit unsigned integers from <paramref name="left"/> and <paramref name="right"/> using <paramref name="mask"/>.
+        /// The high bit of each corresponding <paramref name="mask"/> byte determines the selection.
+        /// If the high bit is set the element of <paramref name="left"/> is selected.
+        /// The element of <paramref name="right"/> is selected otherwise.
+        /// </summary>
+        /// <param name="left">The left vector.</param>
+        /// <param name="right">The right vector.</param>
+        /// <param name="mask">The mask vector.</param>
+        /// <returns>The <see cref="Vector256{T}"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static Vector128<uint> BlendVariable(Vector128<uint> left, Vector128<uint> right, Vector128<uint> mask)
+            => BlendVariable(left.AsByte(), right.AsByte(), mask.AsByte()).AsUInt32();
+
+        /// <summary>
+        /// Count the number of leading zero bits in a mask.
+        /// Similar in behavior to the x86 instruction LZCNT.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        public static ushort LeadingZeroCount(ushort value)
+            => (ushort)(BitOperations.LeadingZeroCount(value) - 16);
+
+        /// <summary>
+        /// Count the number of trailing zero bits in an integer value.
+        /// Similar in behavior to the x86 instruction TZCNT.
+        /// </summary>
+        /// <param name="value">The value.</param>
+        public static ushort TrailingZeroCount(ushort value)
+            => (ushort)(BitOperations.TrailingZeroCount(value << 16) - 16);
+
         /// <summary>
         /// <see cref="ByteToNormalizedFloat"/> as many elements as possible, slicing them down (keeping the remainder).
         /// </summary>

src/ImageSharp/Formats/AnimatedImageFrameMetadata.cs

@@ -0,0 +1,93 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats;
+internal class AnimatedImageFrameMetadata
+{
+    /// <summary>
+    /// Gets or sets the frame color table.
+    /// </summary>
+    public ReadOnlyMemory<Color>? ColorTable { get; set; }
+
+    /// <summary>
+    /// Gets or sets the frame color table mode.
+    /// </summary>
+    public FrameColorTableMode ColorTableMode { get; set; }
+
+    /// <summary>
+    /// Gets or sets the duration of the frame.
+    /// </summary>
+    public TimeSpan Duration { get; set; }
+
+    /// <summary>
+    /// Gets or sets the frame alpha blending mode.
+    /// </summary>
+    public FrameBlendMode BlendMode { get; set; }
+
+    /// <summary>
+    /// Gets or sets the frame disposal mode.
+    /// </summary>
+    public FrameDisposalMode DisposalMode { get; set; }
+}
+
+#pragma warning disable SA1201 // Elements should appear in the correct order
+internal enum FrameBlendMode
+#pragma warning restore SA1201 // Elements should appear in the correct order
+{
+    /// <summary>
+    /// Do not blend. Render the current frame on the canvas by overwriting the rectangle covered by the current frame.
+    /// </summary>
+    Source = 0,
+
+    /// <summary>
+    /// Blend the current frame with the previous frame in the animation sequence within the rectangle covered
+    /// by the current frame.
+    /// If the current has any transparent areas, the corresponding areas of the previous frame will be visible
+    /// through these transparent regions.
+    /// </summary>
+    Over = 1
+}
+
+internal enum FrameDisposalMode
+{
+    /// <summary>
+    /// No disposal specified.
+    /// The decoder is not required to take any action.
+    /// </summary>
+    Unspecified = 0,
+
+    /// <summary>
+    /// Do not dispose. The current frame is not disposed of, or in other words, not cleared or altered when moving to
+    /// the next frame. This means that the next frame is drawn over the current frame, and if the next frame contains
+    /// transparency, the previous frame will be visible through these transparent areas.
+    /// </summary>
+    DoNotDispose = 1,
+
+    /// <summary>
+    /// Restore to background color. When transitioning to the next frame, the area occupied by the current frame is
+    /// filled with the background color specified in the image metadata.
+    /// This effectively erases the current frame by replacing it with the background color before the next frame is displayed.
+    /// </summary>
+    RestoreToBackground = 2,
+
+    /// <summary>
+    /// Restore to previous. This method restores the area affected by the current frame to what it was before the
+    /// current frame was displayed. It essentially "undoes" the current frame, reverting to the state of the image
+    /// before the frame was displayed, then the next frame is drawn. This is useful for animations where only a small
+    /// part of the image changes from frame to frame.
+    /// </summary>
+    RestoreToPrevious = 3
+}
+
+internal enum FrameColorTableMode
+{
+    /// <summary>
+    /// The frame uses the shared color table specified by the image metadata.
+    /// </summary>
+    Global,
+
+    /// <summary>
+    /// The frame uses a color table specified by the frame metadata.
+    /// </summary>
+    Local
+}

src/ImageSharp/Formats/AnimatedImageMetadata.cs

@@ -0,0 +1,32 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.ImageSharp.Formats;
+internal class AnimatedImageMetadata
+{
+    /// <summary>
+    /// Gets or sets the shared color table.
+    /// </summary>
+    public ReadOnlyMemory<Color>? ColorTable { get; set; }
+
+    /// <summary>
+    /// Gets or sets the shared color table mode.
+    /// </summary>
+    public FrameColorTableMode ColorTableMode { get; set; }
+
+    /// <summary>
+    /// Gets or sets the default background color of the canvas when animating.
+    /// This color may be used to fill the unused space on the canvas around the frames,
+    /// as well as the transparent pixels of the first frame.
+    /// The background color is also used when the disposal mode is <see cref="FrameDisposalMode.RestoreToBackground"/>.
+    /// </summary>
+    public Color BackgroundColor { get; set; }
+
+    /// <summary>
+    /// Gets or sets the number of times any animation is repeated.
+    /// <remarks>
+    /// 0 means to repeat indefinitely, count is set as repeat n-1 times. Defaults to 1.
+    /// </remarks>
+    /// </summary>
+    public ushort RepeatCount { get; set; }
+}