@@ -138,61 +138,57 @@ public static LayerTranslator TranslateMatteLayer(
138138
139139 // Walk the collection of layer data and for each pair of matte layer and matted layer, compose them and return a visual
140140 // with the composed result. All other items are not touched.
141- public static IEnumerable < LayerTranslator > ComposeMattedLayers ( CompositionContext context , IEnumerable < ( LayerTranslator translatedLayer , Layer layer ) > items )
141+ public static IEnumerable < LayerTranslator > ComposeMattedLayers ( CompositionContext context , IList < ( LayerTranslator translatedLayer , Layer layer ) > items )
142142 {
143- // Save off the visual for the layer to be matted when we encounter it. The very next
144- // layer is the matte layer.
145- Visual ? mattedVisual = null ;
146- Layer . MatteType matteType = Layer . MatteType . None ;
147-
143+ // After Effects has a concept named "matte layers" which is very similar to masks.
144+ // If there are two adjacent layers in After Effects and first of them has LayerMatteType not equal to MatteType.None
145+ // then we should use the second layer as a "matte" for the first one "mattedLayer". "Matte" layer will not be visible but
146+ // it will define visible region for the "mattedLayer".
147+ //
148148 // NOTE: The items appear in reverse order from how they appear in the original Lottie file.
149149 // This means that the layer to be matted appears right before the layer that is the matte.
150- foreach ( var ( translatedLayer , layer ) in items )
150+ for ( int i = 0 ; i < items . Count ; i ++ )
151151 {
152- var layerIsMattedLayer = false ;
153- layerIsMattedLayer = layer . LayerMatteType != Layer . MatteType . None ;
154-
155- Visual ? visual = null ;
152+ var ( translatedLayer , layer ) = items [ i ] ;
153+ var layerIsMattedLayer = layer . LayerMatteType != Layer . MatteType . None ;
156154
157- if ( translatedLayer . IsShape )
155+ if ( layerIsMattedLayer )
158156 {
159- // If the layer is a shape then we need to wrap it
160- // in a shape visual so that it can be used for matte
161- // composition.
162- if ( layerIsMattedLayer || mattedVisual is not null )
157+ if ( i + 1 < items . Count )
163158 {
164- visual = translatedLayer . GetVisualRoot ( context ) ;
165- }
166- }
167- else
168- {
169- visual = translatedLayer . GetVisualRoot ( context ) ;
170- }
159+ // Move index to the next layer.
160+ i ++ ;
171161
172- if ( visual is not null )
173- {
174- // The layer to be matted comes first. The matte layer is the very next layer.
175- if ( layerIsMattedLayer )
176- {
177- mattedVisual = visual ;
178- matteType = layer . LayerMatteType ;
179- }
180- else if ( mattedVisual is not null )
181- {
182- var compositedMatteVisual = Masks . TranslateMatteLayer ( context , visual , mattedVisual , matteType == Layer . MatteType . Invert ) ;
183- mattedVisual = null ;
184- matteType = Layer . MatteType . None ;
185- yield return compositedMatteVisual ;
186- }
187- else
188- {
189- // Return the visual that was not a matte layer or a layer to be matted.
190- yield return new LayerTranslator . FromVisual ( visual ) ;
162+ var ( translatedLayerNext , _) = items [ i ] ;
163+
164+ Visual ? mattedVisual = translatedLayer . GetVisualRoot ( context ) ;
165+ Visual ? matte = translatedLayerNext . GetVisualRoot ( context ) ;
166+
167+ if ( mattedVisual is not null && matte is not null )
168+ {
169+ // Both matte and mattedLayer are not null -> both are visible, compose them into one visual.
170+ var compositedMatteVisual = TranslateMatteLayer ( context , matte , mattedVisual , layer . LayerMatteType == Layer . MatteType . Invert ) ;
171+ yield return compositedMatteVisual ;
172+ }
173+ else
174+ {
175+ context . Issues . MatteLayerIsNeverVisible ( ) ;
176+
177+ if ( mattedVisual is not null && matte is null && layer . LayerMatteType == Layer . MatteType . Invert )
178+ {
179+ // Matte layer is null, which means that it is never visible and LayerMatteType is equal to Invert.
180+ // In this case we should just return mattedVisual because matte layer is effectively a no-op.
181+ // This is how it works in After Effects.
182+ yield return new LayerTranslator . FromVisual ( mattedVisual ) ;
183+ }
184+ }
191185 }
186+
187+ // We do not have matte layer or both mattedLayer and matte were null so we can just skip them.
192188 }
193189 else
194190 {
195- // Return the shape which does not participate in mattes.
191+ // Just a regular layer, no mattes applied .
196192 yield return translatedLayer ;
197193 }
198194 }
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