encode dibs for windows clipboard

src/pixie/fileformats/bmp.nim

@@ -6,7 +6,9 @@ import bitops, chroma, flatty/binny, pixie/common, pixie/images
 # https://stackoverflow.com/questions/61788908/windows-clipboard-getclipboarddata-for-cf-dibv5-causes-the-image-on-the-clip
 # https://stackoverflow.com/questions/44177115/copying-from-and-to-clipboard-loses-image-transparency/46424800#46424800
 
-const bmpSignature* = "BM"
+const
+  bmpSignature* = "BM"
+  LCS_sRGB = 0x73524742
 
 template failInvalid() =
   raise newException(PixieError, "Invalid BMP buffer, unable to load")
@@ -17,8 +19,7 @@ proc colorMaskShift(color, mask: uint32): uint8 {.inline.} =
 proc decodeDib*(
   data: pointer, len: int, lpBitmapInfo = false
 ): Image {.raises: [PixieError].} =
-  ## Decodes DIB data into an Image.
-
+  ## Decodes DIB data into an image.
   if len < 40:
     failInvalid()
 
@@ -216,8 +217,7 @@ proc decodeDib*(
     result.flipVertical()
 
 proc decodeBmp*(data: string): Image {.raises: [PixieError].} =
-  ## Decodes bitmap data into an Image.
-
+  ## Decodes bitmap data into an image.
   if data.len < 14:
     failInvalid()
 
@@ -231,7 +231,6 @@ proc decodeBmpDimensions*(
   data: string
 ): ImageDimensions {.raises: [PixieError].} =
   ## Decodes the BMP dimensions.
-
   if data.len < 26:
     failInvalid()
 
@@ -242,42 +241,47 @@ proc decodeBmpDimensions*(
   result.width = data.readInt32(18).int
   result.height = abs(data.readInt32(22)).int
 
-proc encodeBmp*(image: Image): string {.raises: [].} =
-  ## Encodes an image into the BMP file format.
+proc encodeDib*(image: Image): string {.raises: [].} =
+  ## Encodes an image into a DIB.
 
-  # BMP Header
-  result.add("BM") # The header field used to identify the BMP
-  result.addUint32(0) # The size of the BMP file in bytes.
-  result.addUint16(0) # Reserved.
-  result.addUint16(0) # Reserved.
-  result.addUint32(122) # The offset to the pixel array.
-
-  # DIB Header
-  result.addUint32(108) # Size of this header
-  result.addInt32(image.width.int32) # Signed integer.
-  result.addInt32(image.height.int32) # Signed integer.
-  result.addUint16(1) # Must be 1 (color planes).
-  result.addUint16(32) # Bits per pixels, only support RGBA.
+  # BITMAPINFO containing BITMAPV5HEADER
+  result.addUint32(124) # Size of this header
+  result.addInt32(image.width.int32) # Signed integer
+  result.addInt32(image.height.int32) # Signed integer
+  result.addUint16(1) # Must be 1 (color planes)
+  result.addUint16(32) # Bits per pixels, only support RGBA
   result.addUint32(3) # BI_BITFIELDS, no pixel array compression used
   result.addUint32(32) # Size of the raw bitmap data (including padding)
   result.addUint32(2835) # Print resolution of the image
   result.addUint32(2835) # Print resolution of the image
   result.addUint32(0) # Number of colors in the palette
   result.addUint32(0) # 0 means all colors are important
-  result.addUint32(uint32(0x000000FF)) # Red channel.
-  result.addUint32(uint32(0x0000FF00)) # Green channel.
-  result.addUint32(uint32(0x00FF0000)) # Blue channel.
-  result.addUint32(uint32(0xFF000000)) # Alpha channel.
-  result.add("Win ") # little-endian.
-  for i in 0 ..< 48:
-    result.addUint8(0) # Unused
+  result.addUint32(uint32(0x000000FF)) # Red channel
+  result.addUint32(uint32(0x0000FF00)) # Green channel
+  result.addUint32(uint32(0x00FF0000)) # Blue channel
+  result.addUint32(uint32(0xFF000000)) # Alpha channel
+  result.addUint32(LCS_sRGB) # Color space
+  result.setLen(result.len + 64) # Unused
+  result.addUint32(0) # BITMAPINFO bmiColors 0
+  result.addUint32(0) # BITMAPINFO bmiColors 1
+  result.addUint32(0) # BITMAPINFO bmiColors 2
 
   for y in 0 ..< image.height:
     for x in 0 ..< image.width:
       let rgba = image[x, image.height - y - 1].rgba()
-      result.addUint8(rgba.r)
-      result.addUint8(rgba.g)
-      result.addUint8(rgba.b)
-      result.addUint8(rgba.a)
+      result.addUint32(cast[uint32](rgba))
+
+proc encodeBmp*(image: Image): string {.raises: [].} =
+  ## Encodes an image into the BMP file format.
+
+  # BMP Header
+  result.add("BM") # The header field used to identify the BMP
+  result.addUint32(0) # The size of the BMP file in bytes
+  result.addUint16(0) # Reserved
+  result.addUint16(0) # Reserved
+  result.addUint32(14 + 12 + 124) # The offset to the pixel array
+
+  # DIB
+  result.add(encodeDib(image))
 
-  result.writeUInt32(2, result.len.uint32)
+  result.writeUint32(2, result.len.uint32)

tests/test_bmp.nim

@@ -1,4 +1,4 @@
-import os, pixie/fileformats/bmp
+import os, pixie, pixie/fileformats/bmp
 
 # block:
 #   var image = newImage(4, 2)
@@ -52,3 +52,13 @@ block:
     #image.writeFile(file.replace("bmpsuite", "output") & ".png")
     doAssert image.width == dimensions.width
     doAssert image.height == dimensions.height
+
+block:
+  let image = newImage(100, 100)
+  image.fill(color(1, 0, 0, 1))
+
+  let
+    encoded = encodeDib(image)
+    decoded = decodeDib(encoded.cstring, encoded.len, true)
+
+  doAssert image.data == decoded.data