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bmp_writer.rb
# coding: binary
class BMP
class Writer
PIXEL_ARRAY_OFFSET = 54
BITS_PER_PIXEL = 24
DIB_HEADER_SIZE = 40
PIXELS_PER_METER = 2835 # 2835 pixels per meter is basically 72dpi
def initialize(width, height)
@width, @height = width, height
@pixels = Array.new(@height) { Array.new(@width) { "000000" } }
end
def [](x,y)
@pixels[y][x]
end
def []=(x,y,value)
@pixels[y][x] = value
end
def save_as(filename)
File.open(filename, "wb") do |file|
write_bmp_file_header(file)
write_dib_header(file)
write_pixel_array(file)
end
end
private
def write_bmp_file_header(file)
file << ["BM", file_size, 0, 0, PIXEL_ARRAY_OFFSET].pack("A2Vv2V")
end
def file_size
PIXEL_ARRAY_OFFSET + pixel_array_size
end
def pixel_array_size
((BITS_PER_PIXEL*@width)/32.0).ceil*4*@height
end
def write_dib_header(file)
file << [DIB_HEADER_SIZE, @width, @height, 1, BITS_PER_PIXEL,
0, pixel_array_size, PIXELS_PER_METER, PIXELS_PER_METER,
0, 0].pack("Vl<2v2V2l<2V2")
end
def write_pixel_array(file)
@pixels.reverse_each do |row|
row.each do |color|
file << pixel_binstring(color)
end
file << row_padding
end
end
def pixel_binstring(rgb_string)
raise ArgumentError unless rgb_string =~ /\A\h{6}\z/
[rgb_string].pack("H6")
end
def row_padding
"\x0" * (@width % 4)
end
end
end
bmp = BMP::Writer.new(2,2)
bmp[0,0] = "ff0000"
bmp[1,0] = "00ff00"
bmp[0,1] = "0000ff"
bmp[1,1] = "ffffff"
bmp.save_as("example_generated.bmp")
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