module ChunkyPNG::Canvas::Drawing

def circle(x0, y0, radius, stroke_color = ChunkyPNG::Color::BLACK, fill_color = ChunkyPNG::Color::TRANSPARENT)
  stroke_color = ChunkyPNG::Color.parse(stroke_color)
  fill_color   = ChunkyPNG::Color.parse(fill_color)
  f = 1 - radius
  ddF_x = 1
  ddF_y = -2 * radius
  x = 0
  y = radius
  compose_pixel(x0, y0 + radius, stroke_color)
  compose_pixel(x0, y0 - radius, stroke_color)
  compose_pixel(x0 + radius, y0, stroke_color)
  compose_pixel(x0 - radius, y0, stroke_color)
  lines = [radius - 1] unless fill_color == ChunkyPNG::Color::TRANSPARENT
  while x < y
    if f >= 0
      y -= 1
      ddF_y += 2
      f += ddF_y
    end
    x += 1
    ddF_x += 2
    f += ddF_x
    unless fill_color == ChunkyPNG::Color::TRANSPARENT
      lines[y] = lines[y] ? [lines[y], x - 1].min : x - 1
      lines[x] = lines[x] ? [lines[x], y - 1].min : y - 1
    end
    compose_pixel(x0 + x, y0 + y, stroke_color)
    compose_pixel(x0 - x, y0 + y, stroke_color)
    compose_pixel(x0 + x, y0 - y, stroke_color)
    compose_pixel(x0 - x, y0 - y, stroke_color)
    unless x == y
      compose_pixel(x0 + y, y0 + x, stroke_color)
      compose_pixel(x0 - y, y0 + x, stroke_color)
      compose_pixel(x0 + y, y0 - x, stroke_color)
      compose_pixel(x0 - y, y0 - x, stroke_color)
    end
  end
  unless fill_color == ChunkyPNG::Color::TRANSPARENT
    lines.each_with_index do |length, y|
      line(x0 - length, y0 - y, x0 + length, y0 - y, fill_color) if length > 0
      line(x0 - length, y0 + y, x0 + length, y0 + y, fill_color) if length > 0 && y > 0
    end
  end
  return self
end

def compose_pixel(x, y, color)
  return unless include_xy?(x, y)
  compose_pixel_unsafe(x, y, ChunkyPNG::Color.parse(color))
end

def compose_pixel_unsafe(x, y, color)
  set_pixel(x, y, ChunkyPNG::Color.compose(color, get_pixel(x, y)))
end

def line_xiaolin_wu(x0, y0, x1, y1, stroke_color, inclusive = true)
  
  stroke_color = ChunkyPNG::Color.parse(stroke_color)
  
  dx = x1 - x0
  sx = dx < 0 ? -1 : 1
  dx *= sx
  dy = y1 - y0
  sy = dy < 0 ? -1 : 1
  dy *= sy
  
  if dy == 0 # vertical line
    x0.step(inclusive ? x1 : x1 - sx, sx) do |x|
      compose_pixel(x, y0, stroke_color)
    end
    
  elsif dx == 0 # horizontal line
    y0.step(inclusive ? y1 : y1 - sy, sy) do |y|
      compose_pixel(x0, y, stroke_color)
    end
    
  elsif dx == dy # diagonal
    x0.step(inclusive ? x1 : x1 - sx, sx) do |x|
      compose_pixel(x, y0, stroke_color)
      y0 += sy
    end
    
  elsif dy > dx  # vertical displacement
    compose_pixel(x0, y0, stroke_color)
    e_acc = 0
    e = ((dx << 16) / dy.to_f).round
    (dy - 1).downto(0) do |i|
      e_acc_temp, e_acc = e_acc, (e_acc + e) & 0xffff
      x0 += sx if (e_acc <= e_acc_temp)
      w = 0xff - (e_acc >> 8)
      compose_pixel(x0, y0, ChunkyPNG::Color.fade(stroke_color, w))
      compose_pixel(x0 + sx, y0 + sy, ChunkyPNG::Color.fade(stroke_color, 0xff - w)) if inclusive || i > 0
      y0 += sy
    end
    compose_pixel(x1, y1, stroke_color) if inclusive
    
  else # horizontal displacement
    compose_pixel(x0, y0, stroke_color)
    e_acc = 0
    e = ((dy << 16) / dx.to_f).round
    (dx - 1).downto(0) do |i|
      e_acc_temp, e_acc = e_acc, (e_acc + e) & 0xffff
      y0 += sy if (e_acc <= e_acc_temp)
      w = 0xff - (e_acc >> 8)
      compose_pixel(x0, y0, ChunkyPNG::Color.fade(stroke_color, w))
      compose_pixel(x0 + sx, y0 + sy, ChunkyPNG::Color.fade(stroke_color, 0xff - w)) if inclusive || i > 0
      x0 += sx
    end
    compose_pixel(x1, y1, stroke_color) if inclusive
  end
  
  return self
end

def polygon(path, stroke_color = ChunkyPNG::Color::BLACK, fill_color = ChunkyPNG::Color::TRANSPARENT)
  
  vector = ChunkyPNG::Vector(*path)
  raise ArgumentError, "A polygon requires at least 3 points" if path.length < 3
  stroke_color = ChunkyPNG::Color.parse(stroke_color)
  fill_color   = ChunkyPNG::Color.parse(fill_color)
  # Fill
  unless fill_color == ChunkyPNG::Color::TRANSPARENT
    vector.y_range.each do |y|
      intersections = []
      vector.edges.each do |p1, p2|
        if (p1.y < y && p2.y >= y) || (p2.y < y && p1.y >= y)
          intersections << (p1.x + (y - p1.y).to_f / (p2.y - p1.y) * (p2.x - p1.x)).round
        end
      end
      intersections.sort!
      0.step(intersections.length - 1, 2) do |i|
        intersections[i].upto(intersections[i + 1]) do |x|
          compose_pixel(x, y, fill_color)
        end
      end
    end
  end
  
  # Stroke
  vector.each_edge do |(from_x, from_y), (to_x, to_y)|
    line(from_x, from_y, to_x, to_y, stroke_color, false)
  end
  return self
end

def rect(x0, y0, x1, y1, stroke_color = ChunkyPNG::Color::BLACK, fill_color = ChunkyPNG::Color::TRANSPARENT)

  stroke_color = ChunkyPNG::Color.parse(stroke_color)
  fill_color   = ChunkyPNG::Color.parse(fill_color)

  # Fill
  unless fill_color == ChunkyPNG::Color::TRANSPARENT
    [x0, x1].min.upto([x0, x1].max) do |x|
      [y0, y1].min.upto([y0, y1].max) do |y|
        compose_pixel(x, y, fill_color)
      end
    end
  end
  
  # Stroke
  line(x0, y0, x0, y1, stroke_color, false)
  line(x0, y1, x1, y1, stroke_color, false)
  line(x1, y1, x1, y0, stroke_color, false)
  line(x1, y0, x0, y0, stroke_color, false)
  
  return self
end