Polygon clipping – Sutherland Hodgeman polygon clipping - The Logic Tutorial

Polygon Clipping – Sutherland Hodgeman Polygon Clipping in Computer Graphics

Overview of Sutherland-Hodgeman Algorithm:

1. Initialization:
• Define the clipping window, usually represented as a rectangular region defined by its minimum and maximum x and y coordinates.
• Define the polygon to be clipped, represented by a sequence of vertices in clockwise or counterclockwise order.
2. Clipping against Each Edge:
• Iterate through each edge of the clipping window.
• For each edge, clip the polygon against that edge.
3. Clipping Process:
• For each edge of the clipping window, perform the following steps:
1. Initialize an empty list to store the vertices of the clipped polygon.
2. Iterate through each consecutive pair of vertices of the original polygon.
3. Check if the current edge of the polygon intersects with the clipping edge.
4. If both vertices lie inside the clipping region, add the second vertex to the output list.
5. If the first vertex lies inside and the second vertex lies outside, add the point of intersection between the edge and the clipping window to the output list, along with the second vertex.
6. If the first vertex lies outside and the second vertex lies inside, add the point of intersection to the output list.
7. If both vertices lie outside, do not add any vertices to the output list.
8. Continue this process until all edges of the polygon are processed.
4. Output:
• The resulting list of vertices represents the clipped polygon.

Example:

Consider a polygon with vertices A(2, 3), B(5, 7), C(7, 4), and D(4, 1), and a clipping window defined by its minimum and maximum coordinates: (3, 3) and (6, 6).

Conclusion:

The Sutherland-Hodgeman algorithm efficiently clips a polygon against a clipping window by iteratively clipping it against each edge of the window. This algorithm is widely used in computer graphics for tasks such as hidden surface removal and rendering. By following a systematic process of determining the visibility of each vertex relative to the clipping window edges, the algorithm produces a clipped polygon that accurately represents the visible portion of the original polygon.