/usr/lib/ruby/vendor_ruby/chunky_png/canvas/adam7_interlacing.rb is in ruby-chunky-png 1.2.8-1.
This file is owned by root:root, with mode 0o644.
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class Canvas
# Methods for decoding and encoding Adam7 interlacing.
#
# Adam7 interlacing extracts 7 pass images out of a single image, that can be encoded to a
# stream separately so the image can be built up progressively. The module is included into
# ChunkyPNG canvas and is used to extract the pass images from the original image, or to
# reconstruct an original image from separate pass images.
module Adam7Interlacing
# Returns an array with the x-shift, x-offset, y-shift and y-offset for the requested pass.
# @param [Integer] pass The pass number, should be in 0..6.
def adam7_multiplier_offset(pass)
[3 - (pass >> 1), (pass & 1 == 0) ? 0 : 8 >> ((pass + 1) >> 1),
pass == 0 ? 3 : 3 - ((pass - 1) >> 1), (pass == 0 || pass & 1 == 1) ? 0 : 8 >> (pass >> 1)]
end
# Returns the pixel dimensions of the requested pass.
# @param [Integer] pass The pass number, should be in 0..6.
# @param [Integer] original_width The width of the original image.
# @param [Integer] original_height The height of the original image.
def adam7_pass_size(pass, original_width, original_height)
x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass)
[ (original_width - x_offset + (1 << x_shift) - 1) >> x_shift,
(original_height - y_offset + (1 << y_shift) - 1) >> y_shift]
end
# Returns an array of the dimension of all the pass images.
# @param [Integer] original_width The width of the original image.
# @param [Integer] original_height The height of the original image.
# @return [Array<Array<Integer>>] Returns an array with 7 pairs of dimensions.
# @see #adam7_pass_size
def adam7_pass_sizes(original_width, original_height)
(0...7).map { |pass| adam7_pass_size(pass, original_width, original_height) }
end
# Merges a pass image into a total image that is being constructed.
# @param [Integer] pass The pass number, should be in 0..6.
# @param [ChunkyPNG::Canvas] canvas The image that is being constructed.
# @param [ChunkyPNG::Canvas] subcanvas The pass image that should be merged
def adam7_merge_pass(pass, canvas, subcanvas)
x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass)
for y in 0...subcanvas.height do
for x in 0...subcanvas.width do
new_x = (x << x_shift) | x_offset
new_y = (y << y_shift) | y_offset
canvas[new_x, new_y] = subcanvas[x, y]
end
end
end
# Extracts a pass from a complete image
# @param [Integer] pass The pass number, should be in 0..6.
# @param [ChunkyPNG::Canvas] canvas The image that is being deconstructed.
# @return [ChunkyPNG::Canvas] The extracted pass image.
def adam7_extract_pass(pass, canvas)
x_shift, x_offset, y_shift, y_offset = adam7_multiplier_offset(pass)
sm_pixels = []
y_offset.step(canvas.height - 1, 1 << y_shift) do |y|
x_offset.step(canvas.width - 1, 1 << x_shift) do |x|
sm_pixels << canvas[x, y]
end
end
new_canvas_args = adam7_pass_size(pass, canvas.width, canvas.height) + [sm_pixels]
ChunkyPNG::Canvas.new(*new_canvas_args)
end
end
end
end
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