Fix lossy decoding issue: return value of ParseResiduals was not used

src/ImageSharp/Formats/WebP/IWebPDecoderOptions.cs

@@ -4,7 +4,7 @@
 namespace SixLabors.ImageSharp.Formats.WebP
 {
     /// <summary>
-    /// Image decoder for generating an image out of a webp stream.
+    /// Image decoder options for generating an image out of a webp stream.
     /// </summary>
     internal interface IWebPDecoderOptions
     {

src/ImageSharp/Formats/WebP/Vp8Decoder.cs

@@ -340,7 +340,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
                         info.Limit = 0;  // no filtering.
                     }
 
-                    info.UseInnerFiltering = (byte)i4x4;
+                    info.UseInnerFiltering = i4x4 is 1;
                 }
             }
         }

src/ImageSharp/Formats/WebP/Vp8FilterInfo.cs

@@ -39,9 +39,8 @@ namespace SixLabors.ImageSharp.Formats.WebP
 
         /// <summary>
         /// Gets or sets a value indicating whether to do inner filtering.
-        /// TODO: can this be a bool?
         /// </summary>
-        public byte UseInnerFiltering { get; set; }
+        public bool UseInnerFiltering { get; set; }
 
         /// <summary>
         /// Gets or sets the high edge variance threshold in [0..2].

src/ImageSharp/Formats/WebP/Vp8MacroBlockData.cs

@@ -8,6 +8,9 @@ namespace SixLabors.ImageSharp.Formats.WebP
     /// </summary>
     internal class Vp8MacroBlockData
     {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Vp8MacroBlockData"/> class.
+        /// </summary>
         public Vp8MacroBlockData()
         {
             this.Modes = new byte[16];
@@ -15,7 +18,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
         }
 
         /// <summary>
-        /// Gets or sets the coefficient. 384 coeffs = (16+4+4) * 4*4.
+        /// Gets or sets the coefficients. 384 coeffs = (16+4+4) * 4*4.
         /// </summary>
         public short[] Coeffs { get; set; }
 
@@ -38,7 +41,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
 
         public uint NonZeroUv { get; set; }
 
-        public byte Skip { get; set; }
+        public bool Skip { get; set; }
 
         public byte Segment { get; set; }
     }

src/ImageSharp/Formats/WebP/WebPLookupTables.cs

@@ -444,7 +444,6 @@ namespace SixLabors.ImageSharp.Formats.WebP
 
         static WebPLookupTables()
         {
-            // TODO: maybe use hashset here
             Abs0 = new Dictionary<int, byte>();
             for (int i = -255; i <= 255; ++i)
             {

src/ImageSharp/Formats/WebP/WebPLossyDecoder.cs

@@ -191,7 +191,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
 
             if (dec.UseSkipProbability)
             {
-                block.Skip = (byte)this.bitReader.GetBit(dec.SkipProbability);
+                block.Skip = this.bitReader.GetBit(dec.SkipProbability) is 1;
             }
 
             block.IsI4x4 = this.bitReader.GetBit(145) is 0;
@@ -488,7 +488,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
                         break;
                 }
 
-                this.DoUVTransform(bitsUv >> 0, coeffs.AsSpan(16 * 16), uDst);
+                this.DoUVTransform(bitsUv, coeffs.AsSpan(16 * 16), uDst);
                 this.DoUVTransform(bitsUv >> 8, coeffs.AsSpan(20 * 16), vDst);
 
                 // Stash away top samples for next block.
@@ -545,7 +545,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
                     LossyUtils.SimpleHFilter16(dec.CacheY.Memory.Span, offset, yBps, limit + 4);
                 }
 
-                if (filterInfo.UseInnerFiltering > 0)
+                if (filterInfo.UseInnerFiltering)
                 {
                     LossyUtils.SimpleHFilter16i(dec.CacheY.Memory.Span, offset, yBps, limit);
                 }
@@ -555,7 +555,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
                     LossyUtils.SimpleVFilter16(dec.CacheY.Memory.Span, offset, yBps, limit + 4);
                 }
 
-                if (filterInfo.UseInnerFiltering > 0)
+                if (filterInfo.UseInnerFiltering)
                 {
                     LossyUtils.SimpleVFilter16i(dec.CacheY.Memory.Span, offset, yBps, limit);
                 }
@@ -572,7 +572,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
                     LossyUtils.HFilter8(dec.CacheU.Memory.Span, dec.CacheV.Memory.Span, uvOffset, uvBps, limit + 4, iLevel, hevThresh);
                 }
 
-                if (filterInfo.UseInnerFiltering > 0)
+                if (filterInfo.UseInnerFiltering)
                 {
                     LossyUtils.HFilter16i(dec.CacheY.Memory.Span, yOffset, yBps, limit, iLevel, hevThresh);
                     LossyUtils.HFilter8i(dec.CacheU.Memory.Span, dec.CacheV.Memory.Span, uvOffset, uvBps, limit, iLevel, hevThresh);
@@ -584,7 +584,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
                     LossyUtils.VFilter8(dec.CacheU.Memory.Span, dec.CacheV.Memory.Span, uvOffset, uvBps, limit + 4, iLevel, hevThresh);
                 }
 
-                if (filterInfo.UseInnerFiltering > 0)
+                if (filterInfo.UseInnerFiltering)
                 {
                     LossyUtils.VFilter16i(dec.CacheY.Memory.Span, yOffset, yBps, limit, iLevel, hevThresh);
                     LossyUtils.VFilter8i(dec.CacheU.Memory.Span, dec.CacheV.Memory.Span, uvOffset, uvBps, limit, iLevel, hevThresh);
@@ -820,11 +820,11 @@ namespace SixLabors.ImageSharp.Formats.WebP
             Vp8MacroBlock left = dec.LeftMacroBlock;
             Vp8MacroBlock macroBlock = dec.CurrentMacroBlock;
             Vp8MacroBlockData blockData = dec.CurrentBlockData;
-            int skip = dec.UseSkipProbability ? blockData.Skip : 0;
+            bool skip = dec.UseSkipProbability ? blockData.Skip : false;
 
-            if (skip is 0)
+            if (!skip)
             {
-                this.ParseResiduals(dec, bitreader, macroBlock);
+                skip = this.ParseResiduals(dec, bitreader, macroBlock);
             }
             else
             {
@@ -843,7 +843,7 @@ namespace SixLabors.ImageSharp.Formats.WebP
             {
                 Vp8FilterInfo precomputedFilterInfo = dec.FilterStrength[blockData.Segment, blockData.IsI4x4 ? 1 : 0];
                 dec.FilterInfo[dec.MbX] = (Vp8FilterInfo)precomputedFilterInfo.DeepClone();
-                dec.FilterInfo[dec.MbX].UseInnerFiltering |= (byte)(skip is 0 ? 1 : 0);
+                dec.FilterInfo[dec.MbX].UseInnerFiltering |= !skip;
             }
         }