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[bugfix] Keep png transparency (#1522) 

* keep png transparency

* rewrite to switch case
This commit is contained in:
mushus 2023-02-19 00:52:15 +09:00 committed by GitHub
parent 59b2e10787
commit fe66a2aed2
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 24 additions and 4 deletions
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28
internal/media/png-stripper.go
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@ -78,9 +78,29 @@ import (
"io"
)
// chunkTypeAncillaryBit is whether the first byte of a big-endian uint32 chunk
// type (the first of four ASCII letters) is lower-case.
const chunkTypeAncillaryBit = 0x20000000
const (
chunkTypeIHDR = 0x49484452
chunkTypePLTE = 0x504C5445
chunkTypeIDAT = 0x49444154
chunkTypeIEND = 0x49454E44
chunkTypeTRNS = 0x74524e53
)
func isNecessaryChunkType(chunkType uint32) bool {
switch chunkType {
case chunkTypeIHDR:
return true
case chunkTypePLTE:
return true
case chunkTypeIDAT:
return true
case chunkTypeIEND:
return true
case chunkTypeTRNS:
return true
}
return false
}
// pngAncillaryChunkStripper wraps another io.Reader to strip ancillary chunks,
// if the data is in the PNG file format. If the data isn't PNG, it is passed
@ -179,7 +199,7 @@ func (r *pngAncillaryChunkStripper) Read(p []byte) (int, error) {
// byte trailer, a checksum.
r.pending = int64(binary.BigEndian.Uint32(r.buffer[:4])) + 4
chunkType := binary.BigEndian.Uint32(r.buffer[4:])
r.discard = (chunkType & chunkTypeAncillaryBit) != 0
r.discard = !isNecessaryChunkType(chunkType)
if r.discard {
r.rIndex = r.wIndex
}