Add support for decoding images from a pointer and a length instead of a string (TODO: qoi, ppm)

src/pixie.nim

@@ -49,8 +49,39 @@ proc decodeImageDimensions*(
   ## Decodes an image's dimensions from memory.
   decodeImageDimensions(data.cstring, data.len)
 
+template compare_as(T: typedesc, p,q: pointer): bool =
+  cast[ptr T](p)[] == cast[ptr T](q)[]
+
+proc decodeImage*(data: pointer, len: int): Image {.raises: [PixieError].} =
+  ## Loads an image from memory, from a pointer and a length.
+  if len > 8 and compare_as(uint64, data, pngSignature.addr):
+    decodePng(data, len).convertToImage()
+  elif len > 2 and compare_as(uint16, data, jpegStartOfImage.addr):
+    decodeJpeg(data, len)
+  elif len > 2 and compare_as(array[2,char], data, bmpSignature.cstring):
+    decodeBmp(data, len)
+  elif len > 5 and
+      compare_as(array[5,char], data, xmlSignature.cstring) or 
+      compare_as(array[4,char], data, svgSignature.cstring):
+    # TODO: avoid allocating/initializing string
+    var s = newStringOfCap(len)
+    s.setLen len
+    copyMem(s.cstring, data, len)
+    newImage(parseSvg(s))
+  elif len > 6 and compare_as(array[6,char], data, gifSignatures[0].cstring) or 
+      compare_as(array[6,char], data, gifSignatures[1].cstring):
+    newImage(decodeGif(data, len))
+  # TODO
+  # elif len > (14+8) and compare_as(array[4,char], data, qoiSignature.cstring):
+  #   decodeQoi(data, len).convertToImage()
+  # elif len > 9 and compare_as(array[2,char], data, ppmSignatures[0].cstring) or 
+  #     compare_as(array[2,char], data, ppmSignatures[1].cstring):
+  #   decodePpm(data, len)
+  else:
+    raise newException(PixieError, "Unsupported image file format")
+
 proc decodeImage*(data: string): Image {.raises: [PixieError].} =
-  ## Loads an image from memory.
+  ## Loads an image from memory as a string.
   if data.len > 8 and data.readUint64(0) == cast[uint64](pngSignature):
     decodePng(data).convertToImage()
   elif data.len > 2 and data.readUint16(0) == cast[uint16](jpegStartOfImage):

src/pixie/fileformats/bmp.nim

@@ -227,6 +227,17 @@ proc decodeBmp*(data: string): Image {.raises: [PixieError].} =
 
   decodeDib(data[14].unsafeAddr, data.len - 14)
 
+proc decodeBmp*(data: pointer, len: int): Image {.raises: [PixieError].} =
+  ## Decodes bitmap data into an image.
+  if len < 14:
+    failInvalid()
+
+  # BMP Header
+  if cast[ptr int16](data)[] != cast[ptr int16]("BM".cstring)[]:
+    failInvalid()
+
+  decodeDib(cast[ptr UncheckedArray[char]](data)[14].addr, len - 14)
+
 proc decodeBmpDimensions*(
   data: pointer, len: int
 ): ImageDimensions {.raises: [PixieError].} =

src/pixie/fileformats/gif.nim

@@ -22,12 +22,18 @@ template failInvalid() =
 when defined(release):
   {.push checks: off.}
 
-proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
+template compare_as(T: typedesc, p,q: pointer): bool =
+  cast[ptr T](p)[] == cast[ptr T](q)[]
+
+proc decodeGif*(data: pointer, len: int): Gif {.raises: [PixieError].} =
+  let data = cast[ptr UncheckedArray[uint8]](data)
   ## Decodes GIF data.
-  if data.len < 13:
+  if len < 13:
     failInvalid()
 
-  if data[0 .. 5] notin gifSignatures:
+  if not (len > 6 and 
+      compare_as(array[6,char], data, gifSignatures[0].cstring) or 
+      compare_as(array[6,char], data, gifSignatures[1].cstring)):
     raise newException(PixieError, "Invalid GIF file signature")
 
   result = Gif()
@@ -49,7 +55,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
 
   var pos = 13
 
-  if pos + globalColorTableSize * 3 > data.len:
+  if pos + globalColorTableSize * 3 > len:
     failInvalid()
 
   var
@@ -69,7 +75,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
 
   proc skipSubBlocks() =
     while true: # Skip data sub-blocks
-      if pos + 1 > data.len:
+      if pos + 1 > len:
         failInvalid()
 
       let subBlockSize = data.readUint8(pos).int
@@ -82,7 +88,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
 
   var controlExtension: ControlExtension
   while true:
-    if pos + 1 > data.len:
+    if pos + 1 > len:
       failInvalid()
 
     let blockType = data.readUint8(pos)
@@ -90,7 +96,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
 
     case blockType:
     of 0x2c: # Image
-      if pos + 9 > data.len:
+      if pos + 9 > len:
         failInvalid()
 
       let
@@ -108,7 +114,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
       if imageWidth > screenWidth or imageHeight > screenHeight:
         raise newException(PixieError, "Invalid GIF frame dimensions")
 
-      if pos + localColorTableSize * 3 > data.len:
+      if pos + localColorTableSize * 3 > len:
         failInvalid()
 
       var localColorTable: seq[ColorRGBX]
@@ -123,7 +129,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
           )
           pos += 3
 
-      if pos + 1 > data.len:
+      if pos + 1 > len:
         failInvalid()
 
       let minCodeSize = data.readUint8(pos).int
@@ -135,7 +141,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
       # The image data is contained in a sequence of sub-blocks
       var lzwDataBlocks: seq[(int, int)] # (offset, len)
       while true:
-        if pos + 1 > data.len:
+        if pos + 1 > len:
           failInvalid()
 
         let subBlockSize = data.readUint8(pos).int
@@ -144,7 +150,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
         if subBlockSize == 0:
           break
 
-        if pos + subBlockSize > data.len:
+        if pos + subBlockSize > len:
           failInvalid()
 
         lzwDataBlocks.add((pos, subBlockSize))
@@ -307,7 +313,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
       controlExtension = ControlExtension()
 
     of 0x21: # Extension
-      if pos + 1 > data.len:
+      if pos + 1 > len:
         failInvalid()
 
       let extensionType = data.readUint8(pos + 0)
@@ -316,7 +322,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
       case extensionType:
       of 0xf9:
         # Graphic Control Extension
-        if pos + 1 > data.len:
+        if pos + 1 > len:
           failInvalid()
 
         let blockSize = data.readUint8(pos).int
@@ -325,7 +331,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
         if blockSize != 4:
           failInvalid()
 
-        if pos + blockSize > data.len:
+        if pos + blockSize > len:
           failInvalid()
 
         controlExtension.fields = data.readUint8(pos + 0)
@@ -344,7 +350,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
 
       of 0xff:
         # Application Specific
-        if pos + 1 > data.len:
+        if pos + 1 > len:
           failInvalid()
 
         let blockSize = data.readUint8(pos).int
@@ -353,7 +359,7 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
         if blockSize != 11:
           failInvalid()
 
-        if pos + blockSize > data.len:
+        if pos + blockSize > len:
           failInvalid()
 
         pos += blockSize
@@ -378,6 +384,9 @@ proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
   for interval in result.intervals:
     result.duration += interval
 
+proc decodeGif*(data: string): Gif {.raises: [PixieError].} =
+  return decodeGif(data.cstring, data.len)
+
 proc decodeGifDimensions*(
   data: pointer, len: int
 ): ImageDimensions {.raises: [PixieError].} =

src/pixie/fileformats/jpeg.nim

@@ -1092,12 +1092,12 @@ proc buildImage(state: var DecoderState): Image =
     else:
       failInvalid("invalid orientation")
 
-proc decodeJpeg*(data: string): Image {.raises: [PixieError].} =
+proc decodeJpeg*(data: pointer, len: int): Image {.raises: [PixieError].} =
   ## Decodes the JPEG into an Image.
 
   var state = DecoderState()
-  state.buffer = cast[ptr UncheckedArray[uint8]](data.cstring)
-  state.len = data.len
+  state.buffer = cast[ptr UncheckedArray[uint8]](data)
+  state.len = len
 
   while true:
     if state.readUint8() != 0xFF:
@@ -1157,6 +1157,10 @@ proc decodeJpeg*(data: string): Image {.raises: [PixieError].} =
 
   state.buildImage()
 
+proc decodeJpeg*(data: string): Image {.raises: [PixieError].} =
+  ## Decodes the JPEG into an Image.
+  decodeJpeg(data.cstring, data.len)
+
 proc decodeJpegDimensions*(
   data: pointer, len: int
 ): ImageDimensions {.raises: [PixieError].} =