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+namespace Ecng.Drawing;
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+/// <summary>
+/// An animation: its canvas, how many times it plays and its frames. The frames are decoded one at a
+/// time, as they are asked for, so that a long animation never has all its canvases in memory at once.
+/// </summary>
+internal sealed class Animation
+{
+	/// <summary>
+	/// The most frames an animation may have to be decoded.
+	/// </summary>
+	public const int MaxFrames = 512;
+
+	/// <summary>
+	/// The most pixels an animation may take to decode, all frames together: every frame costs its
+	/// canvas, whatever part of it the frame itself covers.
+	/// </summary>
+	public const long MaxPixels = 100_000_000;
+
+	public Animation(int width, int height, int plays, int frameCount, IEnumerable<AnimationFrame> frames)
+	{
+		Width = width;
+		Height = height;
+		Plays = plays;
+		FrameCount = frameCount;
+		Frames = frames ?? throw new ArgumentNullException(nameof(frames));
+	}
+
+	public int Width { get; }
+	public int Height { get; }
+
+	/// <summary>
+	/// How many times the animation plays; 0 - endlessly.
+	/// </summary>
+	public int Plays { get; }
+
+	public int FrameCount { get; }
+
+	/// <summary>
+	/// The frames in order. Enumerating decodes them; each comes as a picture of its own that the caller may change.
+	/// </summary>
+	public IEnumerable<AnimationFrame> Frames { get; }
+
+	/// <summary>
+	/// The same animation with every frame replaced by what <paramref name="change"/> makes of it.
+	/// </summary>
+	public Animation Select(int width, int height, Func<RasterImage, RasterImage> change)
+		=> new(width, height, Plays, FrameCount, Frames.Select(frame => frame.WithImage(change(frame.Image))));
+
+	/// <summary>
+	/// Refuses an animation that takes more work than the decoders do for one file.
+	/// </summary>
+	/// <param name="frames">Number of frames.</param>
+	/// <param name="pixels">Pixels to decode and composite, all frames together.</param>
+	/// <exception cref="InvalidDataException">The animation is beyond <see cref="MaxFrames"/> or <see cref="MaxPixels"/>.</exception>
+	public static void EnsureWithinBudget(int frames, long pixels)
+	{
+		if (frames > MaxFrames)
+			throw new InvalidDataException($"The animation has {frames} frames: more than the {MaxFrames} that are decoded.");
+
+		if (pixels > MaxPixels)
+			throw new InvalidDataException($"The animation takes {pixels} pixels to decode: more than the {MaxPixels} that are decoded.");
+	}
+}
@@ -0,0 +1,46 @@
+namespace Ecng.Drawing;
+
+using System;
+
+/// <summary>
+/// One frame of an animation: the whole canvas as it looks while the frame is shown, and for how long.
+/// </summary>
+internal sealed class AnimationFrame
+{
+	/// <param name="image">The composited canvas.</param>
+	/// <param name="delayNumerator">Numerator of the time the frame is shown for, in seconds.</param>
+	/// <param name="delayDenominator">Denominator of that time; greater than zero.</param>
+	public AnimationFrame(RasterImage image, int delayNumerator, int delayDenominator)
+	{
+		Image = image ?? throw new ArgumentNullException(nameof(image));
+
+		if (delayNumerator < 0)
+			throw new ArgumentOutOfRangeException(nameof(delayNumerator));
+
+		if (delayDenominator <= 0)
+			throw new ArgumentOutOfRangeException(nameof(delayDenominator));
+
+		DelayNumerator = delayNumerator;
+		DelayDenominator = delayDenominator;
+	}
+
+	public RasterImage Image { get; }
+
+	/// <summary>
+	/// The frame is shown for <see cref="DelayNumerator"/> / <see cref="DelayDenominator"/> of a second:
+	/// kept as the fraction the file states, so that writing it back changes nothing.
+	/// </summary>
+	public int DelayNumerator { get; }
+
+	/// <inheritdoc cref="DelayNumerator"/>
+	public int DelayDenominator { get; }
+
+	public int DelayMilliseconds
+		=> (int)Math.Min(int.MaxValue, Math.Round(DelayNumerator * 1000.0 / DelayDenominator, MidpointRounding.AwayFromZero));
+
+	/// <summary>
+	/// The same timing over another picture.
+	/// </summary>
+	public AnimationFrame WithImage(RasterImage image)
+		=> new(image, DelayNumerator, DelayDenominator);
+}