Add VP8 encoding tests

src/ImageSharp/Formats/WebP/Lossy/Vp8EncIterator.cs

@@ -367,17 +367,17 @@ namespace SixLabors.ImageSharp.Formats.WebP.Lossy
                 this.ImportLine(v.Slice(uvStartIdx - 1), uvStride, vLeft.Slice(1), uvh, 8);
             }
 
-            Span<byte> yTop = this.YTop.Slice(this.yTopIdx);
+            Span<byte> yTop = this.YTop.Slice(this.yTopIdx, 16);
             if (this.Y == 0)
             {
                 yTop.Fill(127);
-                this.UvTop.GetSpan().Fill(127);
+                this.UvTop.Slice(this.uvTopIdx, 16).Fill(127);
             }
             else
             {
                 this.ImportLine(y.Slice(yStartIdx - yStride), 1, yTop, w, 16);
-                this.ImportLine(u.Slice(uvStartIdx - uvStride), 1, this.UvTop.GetSpan().Slice(8), uvw, 8);
-                this.ImportLine(v.Slice(uvStartIdx - uvStride), 1, this.UvTop.GetSpan().Slice(8), uvw, 8);
+                this.ImportLine(u.Slice(uvStartIdx - uvStride), 1, this.UvTop.Slice(this.uvTopIdx, 8), uvw, 8);
+                this.ImportLine(v.Slice(uvStartIdx - uvStride), 1, this.UvTop.Slice(this.uvTopIdx + 8, 8), uvw, 8);
             }
         }
 

src/ImageSharp/Formats/WebP/Lossy/Vp8Encoder.cs

@@ -224,7 +224,7 @@ namespace SixLabors.ImageSharp.Formats.WebP.Lossy
             var alphas = new int[WebPConstants.MaxAlpha + 1];
             this.alpha = this.MacroBlockAnalysis(width, height, it, y, u, v, yStride, uvStride, alphas, out this.uvAlpha);
 
-            // Analysis is done, proceed to actual coding.
+            // Analysis is done, proceed to actual encoding.
 
             // TODO: EncodeAlpha();
             this.segmentHeader = new Vp8EncSegmentHeader(4);

tests/ImageSharp.Tests/Formats/WebP/WebPEncoderTests.cs

@@ -24,11 +24,9 @@ namespace SixLabors.ImageSharp.Tests.Formats.WebP
                 Quality = quality
             };
 
-            using (Image<TPixel> image = provider.GetImage())
-            {
-                var testOutputDetails = string.Concat("lossless", "_q", quality);
-                image.VerifyEncoder(provider, "webp", testOutputDetails, encoder);
-            }
+            using Image<TPixel> image = provider.GetImage();
+            var testOutputDetails = string.Concat("lossless", "_q", quality);
+            image.VerifyEncoder(provider, "webp", testOutputDetails, encoder);
         }
 
         [Theory]
@@ -46,14 +44,53 @@ namespace SixLabors.ImageSharp.Tests.Formats.WebP
             {
                 Lossy = false,
                 Method = method,
-                Quality = 100
+                Quality = 75
             };
 
-            using (Image<TPixel> image = provider.GetImage())
+            using Image<TPixel> image = provider.GetImage();
+            var testOutputDetails = string.Concat("lossless", "_m", method);
+            image.VerifyEncoder(provider, "webp", testOutputDetails, encoder);
+        }
+
+        [Theory]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 100)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 75)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 20)]
+        public void Encode_Lossy_WithDifferentQuality_Works<TPixel>(TestImageProvider<TPixel> provider, int quality)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            var encoder = new WebPEncoder()
             {
-                var testOutputDetails = string.Concat("lossless", "_m", method);
-                image.VerifyEncoder(provider, "webp", testOutputDetails, encoder);
-            }
+                Lossy = true,
+                Quality = quality
+            };
+
+            using Image<TPixel> image = provider.GetImage();
+            var testOutputDetails = string.Concat("lossy", "_q", quality);
+            image.VerifyEncoder(provider, "webp", testOutputDetails, encoder);
+        }
+
+        [Theory]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 0)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 1)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 2)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 3)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 4)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 5)]
+        [WithFile(Lossy.NoFilter06, PixelTypes.Rgba32, 6)]
+        public void Encode_Lossy_WithDifferentMethods_Works<TPixel>(TestImageProvider<TPixel> provider, int method)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            var encoder = new WebPEncoder()
+            {
+                Lossy = true,
+                Method = method,
+                Quality = 75
+            };
+
+            using Image<TPixel> image = provider.GetImage();
+            var testOutputDetails = string.Concat("lossy", "_m", method);
+            image.VerifyEncoder(provider, "webp", testOutputDetails, encoder);
         }
     }
 }