Class: PNG::Canvas

Inherits:
Object
  • Object
show all
Defined in:
lib/PatchedPNG.rb

Overview

PNG canvas

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(height, width, background = Color::White) ⇒ Canvas

Returns a new instance of Canvas.



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# File 'lib/PatchedPNG.rb', line 194

def initialize(height, width, background = Color::White)
  @height = height
  @width = width
  @data = Array.new(@width) { |x| Array.new(@height) { background } }
end

Instance Attribute Details

#data ⇒ Object (readonly)

Raw data



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# File 'lib/PatchedPNG.rb', line 192

def data
  @data
end

#height ⇒ Object (readonly)

Height of the canvas



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# File 'lib/PatchedPNG.rb', line 182

def height
  @height
end

#width ⇒ Object (readonly)

Width of the canvas



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# File 'lib/PatchedPNG.rb', line 187

def width
  @width
end

Instance Method Details

#[](x, y) ⇒ Object

Retrieves the color of the pixel at (x, y).



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# File 'lib/PatchedPNG.rb', line 203

def [](x, y)
  raise "bad x value #{x} >= #{@height}" if x >= @height
  raise "bad y value #{y} >= #{@width}" if y >= @width
  @data[y][x]
end

#[]=(x, y, color) ⇒ Object

Sets the color of the pixel at (x, y) to color.



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# File 'lib/PatchedPNG.rb', line 212

def []=(x, y, color)
  raise "bad x value #{x} >= #{@height}" if x >= @height
  raise "bad y value #{y} >= #{@width}"  if y >= @width
  @data[y][x] = color
end

#each ⇒ Object

Iterates over each pixel in the canvas.



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# File 'lib/PatchedPNG.rb', line 221

def each
  @data.each_with_index do |row, y|
    row.each_with_index do |pixel, x|
      yield x, y, color
    end
  end
end

#line(x0, y0, x1, y1, color) ⇒ Object

Draws a line using Xiaolin Wu’s antialiasing technique.

en.wikipedia.org/wiki/Xiaolin_Wu’s_line_algorithm



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# File 'lib/PatchedPNG.rb', line 241

def line(x0, y0, x1, y1, color)
  dx = x1 - x0
  sx = dx < 0 ? -1 : 1
  dx *= sx # TODO: abs?
  dy = y1 - y0

  # 'easy' cases
  if dy == 0 then
    Range.new(*[x0,x1].sort).each do |x|
      point(x, y0, color)
    end
    return
  end

  if dx == 0 then
    (y0..y1).each do |y|
      point(x0, y, color)
    end
    return
  end

  if dx == dy then
    Range.new(*[x0,x1].sort).each do |x|
      point(x, y0, color)
      y0 += 1
    end
    return
  end

  # main loop
  point(x0, y0, color)
  e_acc = 0
  if dy > dx then # vertical displacement
    e = (dx << 16) / dy
    (y0...y1-1).each do |i|
      e_acc_temp, e_acc = e_acc, (e_acc + e) & 0xFFFF
      x0 = x0 + sx if (e_acc <= e_acc_temp) 
      w = 0xFF-(e_acc >> 8)
      point(x0, y0, color.intensity(w))
      y0 = y0 + 1
      point(x0 + sx, y0, color.intensity(0xFF-w))
    end
    point(x1, y1, color)
    return
  end

  # horizontal displacement
  e = (dy << 16) / dx
  (x0...(x1-sx)).each do |i|
    e_acc_temp, e_acc = e_acc, (e_acc + e) & 0xFFFF
    y0 += 1 if (e_acc <= e_acc_temp)
    w = 0xFF-(e_acc >> 8)
    point(x0, y0, color.intensity(w))
    x0 += sx
    point(x0, y0 + 1, color.intensity(0xFF-w))
  end
  point(x1, y1, color)
end

#point(x, y, color) ⇒ Object

Blends color onto the color at point (x, y).



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# File 'lib/PatchedPNG.rb', line 232

def point(x, y, color)
  self[x,y] = self[x,y].blend(color)
end