Boundry Fill Algorithm

Boundary Fill Algorithm is a computer graphics algorithm used to fill a bounded area with a specified color. It works by filling a contiguous area of color, starting from a specified point on the boundary of the area and proceeding inward.

The algorithm can be implemented using two approaches:

1. The 4-connected boundary fill algorithm, where a point is considered to be a neighbor if it shares an edge with the current point.

2. The 8-connected boundary fill algorithm, where a point is considered to be a neighbor if it shares an edge or a corner with the current point.

Here are the detailed steps for implementing the 4-connected boundary fill algorithm:

1. Choose a seed point on the boundary of the area to be filled.

2. Set the color of the seed point to the desired fill color.

3. Check the color of the neighboring pixels of the seed point. If their color is not the boundary color and not the fill color, then set their color to the fill color and add them to a list of pixels to be checked.

4. Repeat step 3 for each pixel in the list until all adjacent pixels have been checked.

5. Remove each pixel from the list as it is checked to avoid processing it multiple times.

6. Repeat step 4 and 5 until the entire area is filled.

To implement the 8-connected boundary fill algorithm, we only need to modify step 3 to check the diagonal neighbors in addition to the adjacent ones.

One issue with the basic boundary fill algorithm is that it can go into an infinite loop if it encounters a pixel that has already been filled. To prevent this, we can add a boundary condition to check if the current pixel has already been filled before adding it to the list of pixels to be checked.

Another issue is that the algorithm may fill unwanted pixels if there are gaps or holes inside the boundary. To overcome this, we can use the boundary fill algorithm with the boundary condition to detect and fill the holes.

Overall, the boundary fill algorithm is simple and easy to implement but may suffer from stack overflow issues due to recursive function calls. To overcome this, we can use a non-recursive approach such as the scan-line algorithm or the queue-based approach.