diff options
Diffstat (limited to 'src/img/png.nim')
| -rw-r--r-- | src/img/png.nim | 67 |
1 files changed, 49 insertions, 18 deletions
diff --git a/src/img/png.nim b/src/img/png.nim index 7f4d8493..bd7e6206 100644 --- a/src/img/png.nim +++ b/src/img/png.nim @@ -132,8 +132,7 @@ func spp(reader: PNGReader): int = of pcTrueColorWithAlpha: return 4 func scanlen(reader: PNGReader): int {.inline.} = - let w = reader.width + 1 - return (w * reader.spp * int(reader.bitDepth) + 7) div 8 + return 1 + (reader.width * reader.spp * int(reader.bitDepth) + 7) div 8 proc handleError(reader: var PNGReader; msg: string) = #TODO proper error handling? @@ -258,28 +257,55 @@ proc readtRNS(reader: var PNGReader) = for i in 0 ..< reader.palette.len: reader.palette[i].a = reader.readU8() +func paethPredictor(a, b, c: uint16): uint16 = + let pa0 = int(b) - int(c) + let pb0 = int(a) - int(c) + let pa = abs(pa0) + let pb = abs(pb0) + let pc = abs(pa0 + pb0) + return if pa <= pb and pa <= pc: a elif pb <= pc: b else: c + proc unfilter(reader: var PNGReader; irow: openArray[uint8]; bpp: int) = # none, sub, up -> replace uprow directly # average, paeth -> copy to temp array, then replace uprow - let fil = irow[0] - let w = reader.width - case fil + case irow[0] of 0u8: # none - copyMem(addr reader.uprow[0], unsafeAddr irow[1], w) + copyMem(addr reader.uprow[0], unsafeAddr irow[1], irow.len) of 1u8: # sub for i in 1 ..< irow.len: let j = i - 1 # skip filter byte - reader.uprow[j] = irow[i] - if j - bpp >= 0: - reader.uprow[j] += irow[j - bpp] + let aidx = j - bpp + let x = uint16(irow[i]) + let a = if aidx >= 0: uint16(reader.uprow[aidx]) else: 0u16 + reader.uprow[j] = uint8((x + a) and 0xFF) of 2u8: # up for i in 1 ..< irow.len: let j = i - 1 # skip filter byte - reader.uprow[j] += irow[i] + let x = uint16(irow[i]) + let b = uint16(reader.uprow[j]) + reader.uprow[j] = uint8((x + b) and 0xFF) of 3u8: # average - reader.err "average not implemented yet" + for i in 1 ..< irow.len: + let j = i - 1 # skip filter byte + let aidx = j - bpp + let x = uint16(irow[i]) + let a = if aidx >= 0: uint16(reader.uprow[aidx]) else: 0u16 + let b = uint16(reader.uprow[j]) + reader.uprow[j] = uint8((x + (a + b) div 2) and 0xFF) of 4u8: # paeth - reader.err "paeth not implemented yet" + var cmap: array[8, uint16] # max bpp is 16 bit with true color = 4 * 2 + var k = 0 + for i in 1 ..< irow.len: + let j = i - 1 # skip filter byte + let aidx = j - bpp + let x = uint16(irow[i]) + let a = if aidx >= 0: uint16(reader.uprow[aidx]) else: 0u16 + let b = uint16(reader.uprow[j]) + let kk = k mod bpp + let c = cmap[kk] + cmap[kk] = b + reader.uprow[j] = uint8((x + paethPredictor(a, b, c)) and 0xFF) + inc k else: reader.err "got invalid filter" @@ -340,11 +366,16 @@ proc writepxs(reader: var PNGReader; crow: var openArray[RGBAColor]) = crow[x] = rgba(n, n, n, a) of pcTrueColorWithAlpha: let step = int(reader.bitDepth) div 8 + var i = 0 for x in 0 ..< crow.len: - let r = reader.uprow[x * step] - let g = reader.uprow[(x + 1) * step] - let b = reader.uprow[(x + 2) * step] - let a = reader.uprow[(x + 3) * step] + let r = reader.uprow[i] + i += step + let g = reader.uprow[i] + i += step + let b = reader.uprow[i] + i += step + let a = reader.uprow[i] + i += step crow[x] = rgba(r, g, b, a) proc readPLTE(reader: var PNGReader) = @@ -404,10 +435,10 @@ proc readIDAT(reader: var PNGReader) = for y in reader.atline ..< maxline: let yi = y * sl assert yi + sl - 1 < reader.idatAt - reader.unfilter(toOpenArray(reader.idatBuf, yi, yi + sl - 1), bpp) + reader.unfilter(reader.idatBuf.toOpenArray(yi, yi + sl - 1), bpp) if unlikely(reader.bmp == nil): return let yj = y * reader.width - reader.writepxs(toOpenArray(bmp.px, yj, yj + reader.width - 1)) + reader.writepxs(bmp.px.toOpenArray(yj, yj + reader.width - 1)) proc readIEND(reader: var PNGReader) = if reader.i < reader.limit: |