Area Clipping or Polygon Clipping

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Area Clipping or Polygon Clipping
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Sutherland Hodgeman Method

• Clip the polygon by processing the polygon
  boundary as a whole against each window.
• Process all polygon vertices against each clip
  rectangle boundary in turn.
• First clip the polygon against the left boundary
  to produce a new sequence of vertices.
• The new sequence of vertices is then successive
  passed to right, bottom and top boundary clipper.
• At each step a new sequence of output vertices is
  generated and passed to the next boundary clipper

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Sutherland-HodgmanPolygon Clipping

• Input each edge (vertex pair) successively.
• Output is a new list of vertices.
• Each edge goes through 4 clippers.
• The rule for each edge for each clipper is
• If first input vertex is outside, and second is
  inside, output the intersection and the second
  vertex
• If both input vertices are inside, then just
  output second vertex
• If first input vertex is inside, and second is
  outside, output is the intersection
• If both vertices are outside, output is nothing.
• The last vertex in the list is always added to
  the first vertex

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Sutherland-Hodgeman Polygon Clipping Four
possible scenarios at each clipper
outside inside
outside inside
outside inside
outside inside
v2
v2
v2
v2
v1
v1
v1
v1
v1
v1
Outside to inside Output v1 and v2
Inside to inside Output v2
Inside to outside Output v1
Outside to outside Output nothing
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• The last vertex in the list is always added to
  the first vertex

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Sutherland-Hodgeman Polygon Clipping
v2
Figure 6-27, page 332
v2
v3
v1
v3
Right Clipper
Bottom Clipper
Top Clipper
Left Clipper
v1
v2
v2v3
v2v1
v1
v2v2
v2
v2
v1v2
v2
v2v3
v3
v3v1
v1v2
v2
v2v3
v2
v3v1
v3v1
v1
v1v2
v1v2
v2v2
v3v1
v2
v1v2
v2
v2v2
v2
v2v2
Edges Output
Edges Output
Edges Output
Edges Output
Final
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