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@ -361,7 +361,10 @@ internal sealed class GifEncoderCore |
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: Color.Transparent; |
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// Deduplicate and quantize the frame capturing only required parts.
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(bool difference, Rectangle bounds) = |
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// Pixels matching the previous frame are replaced with the transparent placeholder.
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// When the entire frame matches there is no captured difference, but every pixel is
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// still a placeholder, so a transparent index is always required for additional frames.
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(_, Rectangle bounds) = |
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AnimationUtilities.DeDuplicatePixels( |
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this.configuration, |
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previous, |
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@ -378,7 +381,7 @@ internal sealed class GifEncoderCore |
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bounds, |
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metadata, |
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useLocal, |
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difference, |
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true, |
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transparencyIndex, |
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background); |
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@ -403,7 +406,7 @@ internal sealed class GifEncoderCore |
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Rectangle bounds, |
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GifFrameMetadata metadata, |
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bool useLocal, |
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bool hasDuplicates, |
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bool requiresTransparency, |
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int transparencyIndex, |
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Color transparentColor) |
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where TPixel : unmanaged, IPixel<TPixel> |
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@ -417,9 +420,11 @@ internal sealed class GifEncoderCore |
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// We can use the color data from the decoded metadata here.
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// We avoid dithering by default to preserve the original colors.
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ReadOnlyMemory<Color> palette = metadata.LocalColorTable.Value; |
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if (hasDuplicates && !metadata.HasTransparency) |
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if (requiresTransparency && !metadata.HasTransparency) |
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{ |
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// Duplicates were captured but the metadata does not have transparency.
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// The frame was de-duplicated against the previous frame, replacing matching
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// pixels with the transparent placeholder, but the metadata does not yet carry
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// a transparent index. Reserve one so those pixels encode as transparent.
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metadata.HasTransparency = true; |
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if (palette.Length < 256) |
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@ -480,7 +485,7 @@ internal sealed class GifEncoderCore |
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metadata.TransparencyIndex = ClampIndex(derivedTransparencyIndex); |
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if (hasDuplicates) |
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if (requiresTransparency) |
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{ |
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metadata.HasTransparency = true; |
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} |
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@ -492,11 +497,19 @@ internal sealed class GifEncoderCore |
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// Individual frames, though using the shared palette, can use a different transparent index
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// to represent transparency.
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// A difference was captured but the metadata does not have transparency.
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if (hasDuplicates && !metadata.HasTransparency) |
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// The frame was de-duplicated against the previous frame, replacing matching pixels with
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// the transparent placeholder. When the whole frame matches there is no captured difference,
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// yet every pixel is still a placeholder, so we must always reserve a transparent index here;
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// otherwise the placeholder pixels are matched to the nearest (typically darkest) palette color.
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if (requiresTransparency && !metadata.HasTransparency) |
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{ |
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metadata.HasTransparency = true; |
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transparencyIndex = globalFrameQuantizer.Palette.Length; |
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// Normally we pad one index past the palette so the (out of range) value is treated as
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// transparent by decoders without growing the color table. A full 256-color palette leaves
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// no room to pad within the 8-bit index space (index 256 wraps to 0 when written and exceeds
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// the maximum GIF bit depth), so reuse the last in-range index for transparency instead.
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transparencyIndex = Math.Min(globalFrameQuantizer.Palette.Length, byte.MaxValue); |
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metadata.TransparencyIndex = ClampIndex(transparencyIndex); |
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} |
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James Jackson-South
2 weeks ago
GitHub
