# HG changeset patch
# User Sam <sam@basx.dev>
# Date 1683825210 -25200
# Node ID ecf2d75f06d8e68d715224aa9cdde0b92112ddc6
# Parent  22122b64f09fd4b598460cd48b551e444ffa6197
add: BMP loader

diff -r 22122b64f09f -r ecf2d75f06d8 src/semicongine/core/imagetypes.nim
--- a/src/semicongine/core/imagetypes.nim	Thu May 11 00:30:44 2023 +0700
+++ b/src/semicongine/core/imagetypes.nim	Fri May 12 00:13:30 2023 +0700
@@ -8,9 +8,10 @@
 
 proc newImage*(width, height: uint32, imagedata: seq[Pixel] = @[]): Image =
   assert width > 0 and height > 0
+  result = new Image
+
   result.imagedata = (if imagedata.len == 0: newSeq[Pixel](width * height) else: imagedata)
   assert width * height == uint32(result.imagedata.len)
 
-  result = new Image
   result.width = width
   result.height = height
diff -r 22122b64f09f -r ecf2d75f06d8 src/semicongine/resources/image.nim
--- a/src/semicongine/resources/image.nim	Thu May 11 00:30:44 2023 +0700
+++ b/src/semicongine/resources/image.nim	Fri May 12 00:13:30 2023 +0700
@@ -1,2 +1,105 @@
+import std/streams
+import std/bitops
+import std/algorithm
 
+import ../core/imagetypes
 
+const COMPRESSION_BI_RGB = 0'u32
+const COMPRESSION_BI_BITFIELDS = 3'u32
+const COMPRESSION_BI_ALPHABITFIELDS = 6'u32
+type
+  BitmapFileHeader = object
+    magicbytes: array[2, char]
+    filesize: uint32
+    reserved1: uint16
+    reserved2: uint16
+    dataStart: uint32
+  DIBHeader = object
+    headersize: uint32
+    width: int32
+    height: int32
+    colorPlanes: uint16
+    bitsPerPixel: uint16
+    compression: uint32
+    imageDataSize: uint32 # unused
+    resolutionX: int32 # unused
+    resolutionY: int32 # unused
+    nColors: uint32 # unused
+    nImportantColors: uint32 # unused
+    bitMaskRed: uint32
+    bitMaskGreen: uint32
+    bitMaskBlue: uint32
+    bitMaskAlpha: uint32
+    colorSpace: array[4, char] # not used yet
+    colorSpaceEndpoints: array[36, uint8] # unused
+    gammaRed: uint32 # not used yet
+    gammaGreen: uint32 # not used yet
+    gammaBlue: uint32 # not used yet
+
+proc loadBitmap(stream: Stream): Image =
+  var
+    bitmapFileHeader: BitmapFileHeader
+    dibHeader: DIBHeader
+
+  for name, value in fieldPairs(bitmapFileHeader):
+    stream.read(value)
+  for name, value in fieldPairs(dibHeader):
+
+    when name in ["bitMaskRed", "bitMaskGreen", "bitMaskBlue"]:
+      if dibHeader.compression in [COMPRESSION_BI_BITFIELDS, COMPRESSION_BI_ALPHABITFIELDS]:
+        stream.read(value)
+    elif name == "bitMaskAlpha":
+      if dibHeader.compression == COMPRESSION_BI_ALPHABITFIELDS:
+        stream.read(value)
+    else:
+      stream.read(value)
+
+    when name == "headersize":
+      if value != 124:
+        raise newException(Exception, "Cannot open image, only BITMAPV5 supported")
+    elif name == "colorPlanes":
+      assert value == 1
+    elif name == "bitsPerPixel":
+      if not (value in [24'u16, 32'u16]):
+        raise newException(Exception, "Cannot open image, only depth of 24 and 32 supported")
+    elif name == "compression":
+      if not (value in [0'u32, 3'u32]):
+        raise newException(Exception, "Cannot open image, only BI_RGB and BI_BITFIELDS are supported compressions")
+    elif name == "colorSpace":
+      swap(value[0], value[3])
+      swap(value[1], value[2])
+  stream.setPosition(int(bitmapFileHeader.dataStart))
+  var
+    padding = ((int32(dibHeader.bitsPerPixel div 8)) * dibHeader.width) mod 4
+    data = newSeq[Pixel](dibHeader.width * abs(dibHeader.height))
+  if padding > 0:
+    padding = 4 - padding
+  for row in 0 ..< abs(dibHeader.height):
+    for col in 0 ..< dibHeader.width:
+
+      var pixel: Pixel = [0'u8, 0'u8, 0'u8, 255'u8]
+      # if we got channeld bitmasks
+      if dibHeader.compression in [COMPRESSION_BI_BITFIELDS, COMPRESSION_BI_ALPHABITFIELDS]:
+        var value = stream.readUint32()
+        pixel[0] = uint8((value and dibHeader.bitMaskRed) shr dibHeader.bitMaskRed.countTrailingZeroBits)
+        pixel[1] = uint8((value and dibHeader.bitMaskGreen) shr dibHeader.bitMaskGreen.countTrailingZeroBits)
+        pixel[2] = uint8((value and dibHeader.bitMaskBlue) shr dibHeader.bitMaskBlue.countTrailingZeroBits)
+        if dibHeader.compression == COMPRESSION_BI_ALPHABITFIELDS:
+          pixel[3] = uint8((value and dibHeader.bitMaskAlpha) shr dibHeader.bitMaskAlpha.countTrailingZeroBits)
+      # if we got plain RGB(A), using little endian
+      elif dibHeader.compression == COMPRESSION_BI_RGB:
+        let nChannels = int(dibHeader.bitsPerPixel) div 8
+        for i in 1 .. nChannels:
+          stream.read(pixel[nChannels - i])
+      else:
+        raise newException(Exception, "Cannot open image, only BI_RGB and BI_BITFIELDS are supported compressions")
+
+      # determine whether we read top-to-bottom or bottom-to-top
+      var row_mult: int = (if dibHeader.height < 0: row else: dibHeader.height - row - 1)
+      data[row_mult * dibHeader.width + col]= pixel
+    stream.setPosition(stream.getPosition() + padding)
+
+  result = newImage(width=uint32(dibHeader.width), height=uint32(abs(dibHeader.height)), imagedata=data)
+
+proc loadBitmap(file: string): Image =
+  loadBitmap(newFileStream(file, fmRead))