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[LottieGen] New optimizer that collapses PreComp layers if they reference the same RefId for AnimatedIcon (#474)
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‎source/LottieData/LottieData.projitems

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<Compile Include="$(MSBuildThisFileDirectory)Mask.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)MergePaths.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)NullLayer.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Optimization\CollapsePreCompsOptimizer.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Optimization\LayerGroup.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Optimization\LayersGraph.cs" />
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<Compile Include="$(MSBuildThisFileDirectory)Optimization\MergeHelper.cs" />

‎source/LottieData/Marker.cs

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@@ -31,5 +31,10 @@ public Marker(
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/// <inheritdoc/>
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public override LottieObjectType ObjectType => LottieObjectType.Marker;
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public Marker WithTimeOffset(double offset)
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{
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return new Marker(Name, Frame + offset, DurationInFrames);
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}
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}
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}

‎source/LottieData/Optimization/CollapsePreCompsOptimizer.cs

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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// See the LICENSE file in the project root for more information.
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#nullable enable
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using System.Collections.Generic;
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using System.Linq;
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namespace Microsoft.Toolkit.Uwp.UI.Lottie.LottieData.Optimization
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{
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/// <summary>
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/// This optimizer is trying to optimize the most common Lottie scenario - usage for AnimatedIcon.
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/// AnimatedIcons have many animation segments for different states of the icon and in most
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/// cases they are represented by non-intersecting <see cref="PreCompLayer"/>s. Often these layers
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/// are referencing the same RefId in Asset collection so it means that in fact we can use
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/// only one <see cref="PreCompLayer"/> entry to display an animation for two (or more) identical segments.
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///
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/// This optimizer checks if this is a scenario described above, and if it is, it performs collapsing
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/// of <see cref="PreCompLayer"/>s that have same RefId into one.
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/// </summary>
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#if PUBLIC_LottieData
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public
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#endif
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sealed class CollapsePreCompsOptimizer
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{
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public static LottieComposition Optimize(LottieComposition composition)
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{
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// Example of how this optimization works:
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//
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// m - markers
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//
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// Before optimization:
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//
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// |__ RefId: comp_0 __| |________ RefId: comp_1 ________| |__ RefId : comp_0 __| |__ RefId : comp_2 __|
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// ^ ^ ^ ^ ^ ^ ^ ^
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// m0 m1 m2 m3 m4 m5 m6 m7
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//
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//
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// Step 1 (delete duplicates)
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//
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// |__ RefId: comp_0 __| |________ RefId: comp_1 ________| |__ RefId : comp_2 __|
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// ^ ^ ^ ^ ^ ^ ^ ^
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// m0 m1 m2 m3 m4 m5 m6 m7
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//
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//
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// Step 2 (shift all layers to form one contiguous section)
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//
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// |__ RefId: comp_0 __| |________ RefId: comp_1 ________| |__ RefId : comp_2 __|
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// ^ ^ ^ ^ ^ ^ ^ ^
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// m0 m1 m2 m3 m4 m5 m6 m7
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//
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//
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// Step 3 (final, move all markers to corresponding layers):
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//
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// |__ RefId: comp_0 __| |________ RefId: comp_1 ________| |__ RefId : comp_2 __|
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// ^ ^ ^ ^ ^ ^
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// m0 m1 m2 m3 m6 m7
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// m4 m5
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//
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// We deleted second entry of comp_0, shifted comp_2 to the left and moved markers m4 and m5 to the same spots where m0 and m1 are.
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List<Layer> layers = composition.Layers.GetLayersBottomToTop().ToList();
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// All layers should be pre-comp layers.
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if (!layers.All(a => a is PreCompLayer) || layers.Count == 0)
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{
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return composition;
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}
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// Sort layers by beginning of their time range.
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layers.Sort((a, b) => a.InPoint.CompareTo(b.InPoint));
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// There should not be intersecting layers.
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for (int i = 1; i < layers.Count; i++)
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{
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if (layers[i - 1].OutPoint > layers[i].InPoint)
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{
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return composition;
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}
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}
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// AnimatedIcon uses pair of markers to represent animation segment.
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var startMarkers = new Dictionary<string, Marker>();
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var endMarkers = new Dictionary<string, Marker>();
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foreach (var marker in composition.Markers)
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{
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if (marker.Name.EndsWith("_End"))
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{
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// End markers have %s_End format.
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endMarkers.Add(marker.Name.Substring(0, marker.Name.Length - "_End".Length), marker);
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}
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else if (marker.Name.EndsWith("_Start"))
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{
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// Start markers have %s_Start format.
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startMarkers.Add(marker.Name.Substring(0, marker.Name.Length - "_Start".Length), marker);
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}
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else
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{
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// All markers should have %s_Start or %s_End format.
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return composition;
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}
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}
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// Each Start should match to one End.
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if (startMarkers.Count != endMarkers.Count)
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{
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return composition;
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}
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// Next part of this function will perform PreComps collapsing.
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// We are iterating over layers in order and checking if we can find
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// another layer that has been added to the result and referencing the same RefId.
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//
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// After all layers are collapsed we can end up with some gaps where there is no animations/layers.
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// We can shift all the layers so that there will be no gaps, for this we need layerInPointOffset.
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var layerInPointOffset = new Dictionary<int, double>();
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var layersAfterCollapse = new List<Layer>();
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for (int i = 0; i < layers.Count; i++)
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{
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// Find layer that is referencing the same RefId in already processed layers.
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int previousSameLayer = layersAfterCollapse.FindIndex(layer => ((PreCompLayer)layer).RefId == ((PreCompLayer)layers[i]).RefId);
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if (previousSameLayer == -1)
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{
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// If there were no processed layers, we will offset time of the first layer to start at 0.
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if (layersAfterCollapse.Count == 0)
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{
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layerInPointOffset[i] = -layers[i].InPoint;
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}
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else
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{
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// Otherwise we will offset new layer to start right after previous processed layer.
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layerInPointOffset[i] = layersAfterCollapse[layersAfterCollapse.Count - 1].OutPoint - layers[i].InPoint;
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}
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layersAfterCollapse.Add(layers[i].WithTimeOffset(layerInPointOffset[i]));
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}
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else
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{
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// If we found a layer that is referencing the same RefId we should offset new layer to start at the same point.
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// But we do not need to add this to the layersAfterCompression, since the same layer is already there.
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layerInPointOffset[i] = layersAfterCollapse[previousSameLayer].InPoint - layers[i].InPoint;
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}
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}
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// Next part of this function will offset markers to match new layer positions.
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var markersAfterOffset = new List<Marker>();
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foreach (var key in startMarkers.Keys)
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{
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// For each start there should be an end.
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if (!endMarkers.ContainsKey(key))
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{
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return composition;
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}
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// Each pair of start and end should correspond to some PreCompLayer and should be inside of its time segment.
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int correspondingLayer = layers.FindIndex(
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layer => layer.InPoint <= startMarkers[key].Frame &&
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startMarkers[key].Frame <= endMarkers[key].Frame &&
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endMarkers[key].Frame <= layer.OutPoint);
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if (correspondingLayer == -1)
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{
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return composition;
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}
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// Offset each marker with the same shift as corresponding layer was shifted.
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markersAfterOffset.Add(startMarkers[key].WithTimeOffset(layerInPointOffset[correspondingLayer]));
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markersAfterOffset.Add(endMarkers[key].WithTimeOffset(layerInPointOffset[correspondingLayer]));
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}
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return new LottieComposition(
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composition.Name,
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composition.Width,
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composition.Height,
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layersAfterCollapse[0].InPoint,
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layersAfterCollapse[layersAfterCollapse.Count - 1].OutPoint,
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composition.FramesPerSecond,
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composition.Is3d,
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composition.Version,
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composition.Assets,
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composition.Chars,
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composition.Fonts,
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new LayerCollection(layersAfterCollapse),
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markersAfterOffset,
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composition.ExtraData);
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}
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}
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}

‎source/LottieGen/CommandLineOptions.cs

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internal bool DisableTranslationOptimizer { get; private set; }
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internal bool EnableAnimatedIconOptimizer { get; private set; }
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// The parse error, or null if the parse succeeded.
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// The error should be a sentence (starts with a capital letter, and ends with a period).
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internal string? ErrorDescription { get; private set; }
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sb.Append($" -{nameof(DisableTranslationOptimizer)}");
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}
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if (EnableAnimatedIconOptimizer)
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{
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sb.Append($" -{nameof(EnableAnimatedIconOptimizer)}");
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}
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if (GenerateColorBindings)
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{
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sb.Append($" -{nameof(GenerateColorBindings)}");
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DisableCodeGenOptimizer,
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DisableLottieMergeOptimizer,
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DisableTranslationOptimizer,
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EnableAnimatedIconOptimizer,
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GenerateColorBindings,
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GenerateDependencyObject,
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Help,
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.AddPrefixedKeyword(Keyword.DisableCodeGenOptimizer)
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.AddPrefixedKeyword(Keyword.DisableLottieMergeOptimizer)
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.AddPrefixedKeyword(Keyword.DisableTranslationOptimizer)
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.AddPrefixedKeyword(Keyword.EnableAnimatedIconOptimizer)
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.AddPrefixedKeyword(Keyword.GenerateColorBindings)
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.AddPrefixedKeyword(Keyword.GenerateDependencyObject)
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.AddPrefixedKeyword(Keyword.Help, "?")
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case Keyword.DisableTranslationOptimizer:
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DisableTranslationOptimizer = true;
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break;
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case Keyword.EnableAnimatedIconOptimizer:
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EnableAnimatedIconOptimizer = true;
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break;
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case Keyword.Public:
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Public = true;
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break;

‎source/LottieGen/LottieJsonFileProcessor.cs

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return false;
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}
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if (_options.EnableAnimatedIconOptimizer)
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{
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lottieComposition = CollapsePreCompsOptimizer.Optimize(lottieComposition);
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}
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if (!_options.DisableLottieMergeOptimizer)
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{
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lottieComposition = LottieMergeOptimizer.Optimize(lottieComposition);

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