Class: Pura::Bmp::Encoder

Inherits:
Object
  • Object
show all
Defined in:
lib/pura/bmp/encoder.rb

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(image) ⇒ Encoder

Returns a new instance of Encoder.



13
14
15
 
# File 'lib/pura/bmp/encoder.rb', line 13

def initialize(image)
  @image = image
end

Class Method Details

.encode(image, output_path) ⇒ Object 



6
7
8
9
10
11
 
# File 'lib/pura/bmp/encoder.rb', line 6

def self.encode(image, output_path)
  encoder = new(image)
  data = encoder.encode
  File.binwrite(output_path, data)
  data.bytesize
end

Instance Method Details

#encode ⇒ Object 



17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
 
# File 'lib/pura/bmp/encoder.rb', line 17

def encode
  width = @image.width
  height = @image.height
  pixels = @image.pixels

  stride = ((width * 3) + 3) & ~3 # Row size padded to 4-byte boundary
  padding = stride - (width * 3)
  pixel_data_size = stride * height
  file_size = 14 + 40 + pixel_data_size # File header + info header + pixel data
  pixel_offset = 14 + 40

  out = String.new(encoding: Encoding::BINARY, capacity: file_size)

  # File header (14 bytes)
  out << "BM"
  out << [file_size].pack("V")
  out << [0, 0].pack("vv") # Reserved
  out << [pixel_offset].pack("V")

  # Info header (BITMAPINFOHEADER, 40 bytes)
  out << [40].pack("V")           # Header size
  out << [width].pack("V")        # Width
  out << [height].pack("l<")      # Height (positive = bottom-up)
  out << [1].pack("v")            # Planes
  out << [24].pack("v")           # Bit depth
  out << [0].pack("V")            # Compression (BI_RGB)
  out << [pixel_data_size].pack("V") # Image size
  out << [2835].pack("l<")        # X pixels per meter (~72 DPI)
  out << [2835].pack("l<")        # Y pixels per meter (~72 DPI)
  out << [0].pack("V")            # Colors used
  out << [0].pack("V")            # Colors important

  # Pixel data (bottom-to-top, BGR order)
  pad_bytes = "\x00".b * padding
  (height - 1).downto(0) do |y|
    row_offset = y * width * 3
    width.times do |x|
      off = row_offset + (x * 3)
      r = pixels.getbyte(off)
      g = pixels.getbyte(off + 1)
      b = pixels.getbyte(off + 2)
      out << b.chr << g.chr << r.chr # BGR order
    end
    out << pad_bytes if padding.positive?
  end

  out
end