Sha256: bb1a9e9fa96bc9e402440fa037590e1c608db71fe3a5aeea43cfe9ccbf5dda16
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Contents
module ChunkyPNG
class Canvas
# Methods for decoding and encoding adam7 interlacing
#
module Adam7Interlacing
def adam7_multiplier_offset(pass)
{
:x_shift => 3 - (pass >> 1),
:x_offset => (pass & 1 == 0) ? 0 : 8 >> ((pass + 1) >> 1),
:y_shift => pass == 0 ? 3 : 3 - ((pass - 1) >> 1),
:y_offset => (pass == 0 || pass & 1 == 1) ? 0 : 8 >> (pass >> 1)
}
end
def adam7_pass_size(pass, original_width, original_height)
m_o = adam7_multiplier_offset(pass)
[ (original_width - m_o[:x_offset] + (1 << m_o[:x_shift]) - 1) >> m_o[:x_shift],
(original_height - m_o[:y_offset] + (1 << m_o[:y_shift]) - 1) >> m_o[:y_shift]]
end
def adam7_pass_sizes(original_width, original_height)
(0...7).map { |pass| adam7_pass_size(pass, original_width, original_height) }
end
def adam7_merge_pass(pass, canvas, subcanvas)
m_o = adam7_multiplier_offset(pass)
for y in 0...subcanvas.height do
for x in 0...subcanvas.width do
new_x = (x << m_o[:x_shift]) | m_o[:x_offset]
new_y = (y << m_o[:y_shift]) | m_o[:y_offset]
canvas[new_x, new_y] = subcanvas[x, y]
end
end
canvas
end
def adam7_extract_pass(pass, canvas)
m_o = adam7_multiplier_offset(pass)
sm_pixels = []
m_o[:y_offset].step(canvas.height - 1, 1 << m_o[:y_shift]) do |y|
m_o[:x_offset].step(canvas.width - 1, 1 << m_o[: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
Version data entries
20 entries across 20 versions & 1 rubygems