decode png has ptr+len proc

src/pixie/fileformats/png.nim

@@ -27,7 +27,8 @@ template failInvalid() =
 when defined(release):
   {.push checks: off.}
 
-proc decodeHeader(data: string): PngHeader =
+proc decodeHeader(data: pointer): PngHeader =
+  let data = cast[ptr UncheckedArray[uint8]](data)
   result.width = data.readUint32(0).swap().int
   result.height = data.readUint32(4).swap().int
   result.bitDepth = data.readUint8(8)
@@ -78,18 +79,19 @@ proc decodeHeader(data: string): PngHeader =
   # Not yet supported:
 
   if result.bitDepth == 16:
-    raise newException(PixieError, "PNG 16 bit depth not yet supported")
+    raise newException(PixieError, "PNG 16 bit depth not supported yet")
 
   if result.interlaceMethod != 0:
-    raise newException(PixieError, "Interlaced PNG not yet supported")
+    raise newException(PixieError, "Interlaced PNG not supported yet")
 
-proc decodePalette(data: string): seq[ColorRGB] =
+proc decodePalette(data: pointer, len: int): seq[ColorRGB] =
-  if data.len == 0 or data.len mod 3 != 0:
+  if len == 0 or len mod 3 != 0:
     failInvalid()
 
-  result.setLen(data.len div 3)
+  result.setLen(len div 3)
 
-  for i in 0 ..< data.len div 3:
+  let data = cast[ptr UncheckedArray[uint8]](data)
+  for i in 0 ..< len div 3:
     copyMem(result[i].addr, data[i * 3].unsafeAddr, 3)
 
 proc unfilter(
@@ -165,7 +167,7 @@ proc unfilter(
       discard # Not possible, parseHeader validates
 
 proc decodeImageData(
-  data: string,
+  data: ptr UncheckedArray[uint8],
   header: PngHeader,
   palette: seq[ColorRGB],
   transparency: string,
@@ -183,7 +185,7 @@ proc decodeImageData(
         for (start, len) in idats:
           let op = imageData.len
           imageData.setLen(imageData.len + len)
-          copyMem(imageData[op].addr, data[start].unsafeAddr, len)
+          copyMem(imageData[op].addr, data[start].addr, len)
         try: uncompress(imageData) except ZippyError: failInvalid()
       else:
         let
@@ -341,12 +343,14 @@ proc newImage*(png: Png): Image {.raises: [PixieError].} =
   result.data.toPremultipliedAlpha()
 
 proc decodePngDimensions*(
-  data: string
+  data: pointer, len: int
 ): ImageDimensions {.raises: [PixieError].} =
   ## Decodes the PNG dimensions.
-  if data.len < (8 + (8 + 13 + 4) + 4): # Magic bytes + IHDR + IEND
+  if len < (8 + (8 + 13 + 4) + 4): # Magic bytes + IHDR + IEND
     failInvalid()
 
+  let data = cast[ptr UncheckedArray[uint8]](data)
+
   # PNG file signature
   let signature = cast[array[8, uint8]](data.readUint64(0))
   if signature != pngSignature:
@@ -356,15 +360,23 @@ proc decodePngDimensions*(
   if data.readUint32(8).swap() != 13 or data.readStr(12, 4) != "IHDR":
     failInvalid()
 
-  let header = decodeHeader(data[16 ..< 16 + 13])
+  let header = decodeHeader(data[16].addr)
   result.width = header.width
   result.height = header.height
 
-proc decodePng*(data: string): Png {.raises: [PixieError].} =
+proc decodePngDimensions*(
+  data: string
+): ImageDimensions {.inline, raises: [PixieError].} =
+  ## Decodes the PNG dimensions.
+  decodePngDimensions(data.cstring, data.len)
+
+proc decodePng*(data: pointer, len: int): Png {.raises: [PixieError].} =
   ## Decodes the PNG data.
-  if data.len < (8 + (8 + 13 + 4) + 4): # Magic bytes + IHDR + IEND
+  if len < (8 + (8 + 13 + 4) + 4): # Magic bytes + IHDR + IEND
     failInvalid()
 
+  let data = cast[ptr UncheckedArray[uint8]](data)
+
   # PNG file signature
   let signature = cast[array[8, uint8]](data.readUint64(0))
   if signature != pngSignature:
@@ -384,7 +396,7 @@ proc decodePng*(data: string): Png {.raises: [PixieError].} =
     data.readStr(pos + 4, 4) != "IHDR":
     failInvalid()
   inc(pos, 8)
-  header = decodeHeader(data[pos ..< pos + 13])
+  header = decodeHeader(data[pos].addr)
   prevChunkType = "IHDR"
   inc(pos, 13)
 
@@ -393,7 +405,7 @@ proc decodePng*(data: string): Png {.raises: [PixieError].} =
   inc(pos, 4) # CRC
 
   while true:
-    if pos + 8 > data.len:
+    if pos + 8 > len:
       failInvalid()
 
     let
@@ -404,7 +416,7 @@ proc decodePng*(data: string): Png {.raises: [PixieError].} =
     if chunkLen > high(int32).int:
       failInvalid()
 
-    if pos + chunkLen + 4 > data.len:
+    if pos + chunkLen + 4 > len:
       failInvalid()
 
     case chunkType:
@@ -414,12 +426,12 @@ proc decodePng*(data: string): Png {.raises: [PixieError].} =
       inc counts.PLTE
       if counts.PLTE > 1 or counts.IDAT > 0 or counts.tRNS > 0:
         failInvalid()
-      palette = decodePalette(data[pos ..< pos + chunkLen])
+      palette = decodePalette(data[pos].addr, chunkLen)
     of "tRNS":
       inc counts.tRNS
       if counts.tRNS > 1 or counts.IDAT > 0:
         failInvalid()
-      transparency = data[pos ..< pos + chunkLen]
+      transparency = data.readStr(pos, chunkLen)
       case header.colorType:
       of 0:
         if transparency.len != 2:
@@ -456,7 +468,7 @@ proc decodePng*(data: string): Png {.raises: [PixieError].} =
 
     prevChunkType = chunkType
 
-    if pos == data.len or prevChunkType == "IEND":
+    if pos == len or prevChunkType == "IEND":
       break
 
   if prevChunkType != "IEND":
@@ -468,6 +480,10 @@ proc decodePng*(data: string): Png {.raises: [PixieError].} =
   result.channels = 4
   result.data = decodeImageData(data, header, palette, transparency, idats)
 
+proc decodePng*(data: string): Png {.inline, raises: [PixieError].} =
+  ## Decodes the PNG data.
+  decodePng(data.cstring, data.len)
+
 proc encodePng*(
   width, height, channels: int, data: pointer, len: int
 ): string {.raises: [PixieError].} =