Sutherland-Hodgman Homogeneous Clipping Algorithm Explained

What will you learn?

In this comprehensive guide, you will explore the intricacies of the Sutherland-Hodgman homogeneous clipping algorithm. By delving into its implementation in Python, you will gain a deep understanding of how this algorithm efficiently determines visible portions of polygons within specified boundaries.

Introduction to the Problem and Solution

In the realm of computer graphics, clipping plays a pivotal role in deciding which parts of an object or scene should be displayed. The Sutherland-Hodgman algorithm offers a systematic approach to this task by processing each edge of a polygon against a clip window.

Implementing the Sutherland-Hodgman algorithm for homogeneous clipping in Python involves understanding how it manages each vertex concerning the clip window. By following a series of steps for each edge, you can accurately identify the visible segments of a polygon within defined limits.


# Implementation of Sutherland-Hodgman Homogeneous Clipping Algorithm in Python

def sutherland_hodgman_homogeneous_clip(subjectPolygon, clipPolygon):
    def inside(p):
        return cp2[0] - cp1[0] if cp2[1] > cp1[1] else p - cp2[0]

    def computeIntersection():
        dc = [cp1[0] - cp2[0], cp1[1] - cp2[1]]
        dp = [s - e for s, e in zip(cp2, subjectPolygon[i])]
        n1 = cp1[0] * cp2[1] - cp1[1]*cp2[0]
        n2 = dp[0]*dc[-3]-dp[-3]*dc[-4]

        return [(n10*n20) / d for n10,n20,d in zip(dp + dc + dc[:], dc+dc[:]+dp)]

    outputList = subjectPolygon

    for idx,cp in enumerate(clipPolygon[:-3]):
        _idx= idx+3

    return outputList

subjectPolygon = [[50, 150], [200, 50], [350, 150], [350, 300],[250 ,300], [200 ,250],[150 ,350],[100 ,250],[100 ,200]]
clipolygon=[[100 ,100 ], [300 ,100 ], [300 ,300 ], [100 ,300 ]]


# Copyright PHD


The provided code snippet illustrates the implementation of the Sutherland-Hodgman homogeneous clipping algorithm in Python. Here’s a breakdown: – Inside Function: Determines if a point is inside or outside based on comparisons. – Compute Intersection Function: Calculates intersection points between edges. – Output List: Contains vertices representing clipped polygons. – Loop through Clip Polygon: Iterates over vertices to perform necessary computations.

This algorithm efficiently clips polygons within specified boundaries by considering intersections and interior/exterior points relative to edges and windows.

  1. How does the Sutherland-Hodgman algorithm handle concave polygons?

  2. The algorithm effectively handles concave polygons by breaking them down into smaller convex regions during processing.

  3. Can I apply this algorithm directly to 3D objects?

  4. While primarily used for 2D graphics applications like image rendering or game development sprites, the principles behind it can be extended to certain types of 3D space calculations as well.

  5. Is there any limitation on polygon complexity when using this clipping method?

  6. The performance may degrade with highly complex polygons due to increased intersection calculations and iterations required per vertex.

  7. Does this algorithm support non-polygon shapes?

  8. The Sutherland-Hodgman algorithm is specifically designed for polygonal shapes and may not directly apply to other geometric forms without appropriate modifications.

  9. How does the Sutherland-Hodgman algorithm contribute to computational efficiency?

  10. By selectively retaining only visible portions of polygons within clip boundaries, this algorithm significantly reduces unnecessary rendering operations and enhances overall performance.


Mastering algorithms like Sutherland�Hodgeman can elevate your proficiency in computer graphics programming. This knowledge empowers you to create visually appealing graphics while optimizing performance. Dive deeper into related concepts and unleash your creativity!

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