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[bugfix] Keep png transparency (#1522)
* keep png transparency * rewrite to switch case
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@ -78,9 +78,29 @@
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"io"
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"io"
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)
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)
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// chunkTypeAncillaryBit is whether the first byte of a big-endian uint32 chunk
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const (
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// type (the first of four ASCII letters) is lower-case.
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chunkTypeIHDR = 0x49484452
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const chunkTypeAncillaryBit = 0x20000000
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chunkTypePLTE = 0x504C5445
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chunkTypeIDAT = 0x49444154
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chunkTypeIEND = 0x49454E44
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chunkTypeTRNS = 0x74524e53
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)
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func isNecessaryChunkType(chunkType uint32) bool {
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switch chunkType {
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case chunkTypeIHDR:
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return true
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case chunkTypePLTE:
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return true
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case chunkTypeIDAT:
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return true
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case chunkTypeIEND:
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return true
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case chunkTypeTRNS:
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return true
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}
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return false
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}
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// pngAncillaryChunkStripper wraps another io.Reader to strip ancillary chunks,
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// pngAncillaryChunkStripper wraps another io.Reader to strip ancillary chunks,
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// if the data is in the PNG file format. If the data isn't PNG, it is passed
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// if the data is in the PNG file format. If the data isn't PNG, it is passed
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@ -179,7 +199,7 @@ func (r *pngAncillaryChunkStripper) Read(p []byte) (int, error) {
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// byte trailer, a checksum.
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// byte trailer, a checksum.
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r.pending = int64(binary.BigEndian.Uint32(r.buffer[:4])) + 4
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r.pending = int64(binary.BigEndian.Uint32(r.buffer[:4])) + 4
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chunkType := binary.BigEndian.Uint32(r.buffer[4:])
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chunkType := binary.BigEndian.Uint32(r.buffer[4:])
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r.discard = (chunkType & chunkTypeAncillaryBit) != 0
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r.discard = !isNecessaryChunkType(chunkType)
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if r.discard {
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if r.discard {
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r.rIndex = r.wIndex
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r.rIndex = r.wIndex
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}
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}
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