Module: Tabula::CohenSutherlandClipping

Defined in:
lib/tabula/algorithms/cohen_sutherland_clipping.rb

Overview

Cohen-Sutherland line clipping algorithm. Clips a line segment to a rectangular region.

Constant Summary collapse

INSIDE =

Region codes for Cohen-Sutherland algorithm

0b0000
LEFT = 
0b0001
RIGHT = 
0b0010
BOTTOM = 
0b0100
TOP = 
0b1000

Class Method Summary collapse

Class Method Details

.clip(ruling, rect) ⇒ Ruling?

Clip a ruling to a rectangular region

Parameters:

  • ruling (Ruling) —

    the line segment to clip

  • rect (Rectangle) —

    the clipping region

Returns:

  • (Ruling, nil) —

    clipped ruling, or nil if entirely outside



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# File 'lib/tabula/algorithms/cohen_sutherland_clipping.rb', line 19

def clip(ruling, rect)
  x1 = ruling.x1
  y1 = ruling.y1
  x2 = ruling.x2
  y2 = ruling.y2

  min_x = rect.left
  max_x = rect.right
  min_y = rect.top
  max_y = rect.bottom

  code1 = compute_code(x1, y1, min_x, max_x, min_y, max_y)
  code2 = compute_code(x2, y2, min_x, max_x, min_y, max_y)

  loop do
    # Both endpoints inside - trivially accept
    return Ruling.new(x1, y1, x2, y2) if (code1 | code2).zero?

    # Both endpoints share an outside region - trivially reject
    return nil if (code1 & code2).nonzero?

    # At least one endpoint is outside, select it
    code_out = code1.nonzero? ? code1 : code2

    # Find intersection point
    x, y = find_intersection(x1, y1, x2, y2, code_out, min_x, max_x, min_y, max_y)

    # Replace the outside point
    if code_out == code1
      x1 = x
      y1 = y
      code1 = compute_code(x1, y1, min_x, max_x, min_y, max_y)
    else
      x2 = x
      y2 = y
      code2 = compute_code(x2, y2, min_x, max_x, min_y, max_y)
    end
  end
end