add ico and bmp support

lib/load_bmp.rb

@@ -0,0 +1,170 @@
+# frozen_string_literal: true
+
+module LoadBmp
+  module_function
+
+  # rubocop:disable Metrics
+  def call(bmp_bytes)
+    bmp_bytes = bmp_bytes.b
+
+    header_data = parse_bmp_headers(bmp_bytes)
+
+    raw_pixel_data_from_file = extract_raw_pixel_data_blob(
+      bmp_bytes,
+      header_data[:pixel_data_offset],
+      header_data[:bmp_stride],
+      header_data[:height]
+    )
+
+    final_pixel_data = prepare_unpadded_pixel_data_string(
+      raw_pixel_data_from_file,
+      header_data[:bpp],
+      header_data[:width],
+      header_data[:height],
+      header_data[:bmp_stride]
+    )
+
+    bands = header_data[:bpp] / 8
+
+    unless header_data[:bpp] == 24 || header_data[:bpp] == 32
+      raise ArgumentError, "Conversion for #{header_data[:bpp]}-bpp BMP not implemented."
+    end
+
+    image = Vips::Image.new_from_memory(final_pixel_data, header_data[:width], header_data[:height], bands, :uchar)
+
+    image = image.flip(:vertical) if header_data[:orientation] == -1
+
+    image_rgb =
+      if bands == 3
+        Vips::Image.bandjoin([image[2], image[1], image[0]])
+      elsif bands == 4
+        Vips::Image.bandjoin([image[2], image[1], image[0], image[3]])
+      else
+        image
+      end
+
+    if image_rgb.interpretation == :multiband || image_rgb.interpretation == :'b-w'
+      image_rgb = image_rgb.copy(interpretation: :srgb)
+    end
+
+    image_rgb
+  end
+
+  def parse_bmp_headers(bmp_bytes)
+    raise ArgumentError, 'BMP data too short for file header (14 bytes).' if bmp_bytes.bytesize < 14
+
+    signature, pixel_data_offset = bmp_bytes.unpack('a2@10L<')
+
+    raise ArgumentError, "Not a valid BMP file (invalid signature 'BM')." if signature != 'BM'
+
+    raise ArgumentError, 'BMP data too short for info header size field (4 bytes).' if bmp_bytes.bytesize < (14 + 4)
+
+    info_header_size = bmp_bytes.unpack1('@14L<')
+
+    min_expected_info_header_size = 40
+
+    if info_header_size < min_expected_info_header_size
+      raise ArgumentError,
+            "Unsupported BMP info header size: #{info_header_size}. Expected at least #{min_expected_info_header_size}."
+    end
+
+    header_and_info_header_min_bytes = 14 + min_expected_info_header_size
+
+    if bmp_bytes.bytesize < header_and_info_header_min_bytes
+      raise ArgumentError,
+            'BMP data too short for essential BITMAPINFOHEADER fields ' \
+            "(requires #{header_and_info_header_min_bytes} bytes total)."
+    end
+
+    _header_size_check, width, raw_height_from_header, planes, bpp, compression =
+      bmp_bytes.unpack('@14L<l<l<S<S<L<')
+
+    height = 0
+    orientation = -1
+
+    if raw_height_from_header.negative?
+      height = -raw_height_from_header
+      orientation = 1
+    else
+      height = raw_height_from_header
+    end
+
+    raise ArgumentError, 'BMP width must be positive.' if width <= 0
+    raise ArgumentError, 'BMP height must be positive.' if height <= 0
+
+    if compression != 0
+      raise ArgumentError,
+            "Unsupported BMP compression type: #{compression}. Only uncompressed (0) is supported."
+    end
+
+    unless [24, 32].include?(bpp)
+      raise ArgumentError, "Unsupported BMP bits per pixel: #{bpp}. Only 24-bit and 32-bit are supported."
+    end
+
+    raise ArgumentError, "Unsupported BMP planes: #{planes}. Expected 1." if planes != 1
+
+    bytes_per_pixel = bpp / 8
+    row_size_unpadded = width * bytes_per_pixel
+    bmp_stride = (row_size_unpadded + 3) & ~3
+
+    {
+      width:,
+      height:,
+      bpp:,
+      pixel_data_offset:,
+      bmp_stride:,
+      orientation:
+    }
+  end
+
+  def extract_raw_pixel_data_blob(bmp_bytes, pixel_data_offset, bmp_stride, height)
+    expected_pixel_data_size = bmp_stride * height
+
+    if pixel_data_offset + expected_pixel_data_size > bmp_bytes.bytesize
+      actual_available = bmp_bytes.bytesize - pixel_data_offset
+      actual_available = 0 if actual_available.negative?
+      raise ArgumentError,
+            "Pixel data segment (offset #{pixel_data_offset}, expected size #{expected_pixel_data_size}) " \
+            "exceeds BMP file size (#{bmp_bytes.bytesize}). " \
+            "Only #{actual_available} bytes available after offset."
+    end
+
+    raw_pixel_data_from_file = bmp_bytes.byteslice(pixel_data_offset, expected_pixel_data_size)
+
+    if raw_pixel_data_from_file.nil? || raw_pixel_data_from_file.bytesize < expected_pixel_data_size
+      raise ArgumentError,
+            "Extracted pixel data is smaller (#{raw_pixel_data_from_file&.bytesize || 0} bytes) " \
+            "than expected (#{expected_pixel_data_size} bytes based on stride and height)."
+    end
+
+    raw_pixel_data_from_file
+  end
+
+  def prepare_unpadded_pixel_data_string(raw_pixel_data_from_file, bpp, width, height, bmp_stride)
+    bytes_per_pixel = bpp / 8
+    actual_row_width_bytes = width * bytes_per_pixel
+
+    unpadded_rows = Array.new(height)
+    current_offset_in_blob = 0
+
+    height.times do |i|
+      if current_offset_in_blob + actual_row_width_bytes > raw_pixel_data_from_file.bytesize
+        raise ArgumentError,
+              "Not enough data in pixel blob for row #{i}. Offset #{current_offset_in_blob}, " \
+              "row width #{actual_row_width_bytes}, blob size #{raw_pixel_data_from_file.bytesize}"
+      end
+
+      unpadded_row_slice = raw_pixel_data_from_file.byteslice(current_offset_in_blob, actual_row_width_bytes)
+
+      if unpadded_row_slice.nil? || unpadded_row_slice.bytesize < actual_row_width_bytes
+        raise ArgumentError, "Failed to slice a full unpadded row from pixel data blob for row #{i}."
+      end
+
+      unpadded_rows[i] = unpadded_row_slice
+      current_offset_in_blob += bmp_stride
+    end
+
+    unpadded_rows.join
+  end
+  # rubocop:enable Metrics
+end