FloodFill.cs

usingSystem;
usingSystem.Collections.Generic;
usingSkiaSharp;

namespaceAlgorithms.Other;

/// <summary>
/// Flood fill, also called seed fill, is an algorithm that determines and
/// alters the area connected to a given node in a multi-dimensional array with
/// some matching attribute. It is used in the "bucket" fill tool of paint
/// programs to fill connected, similarly-colored areas with a different color.
/// (description adapted from https://en.wikipedia.org/wiki/Flood_fill)
/// (see also: https://www.techiedelight.com/flood-fill-algorithm/).
/// </summary>
publicstaticclassFloodFill
{
privatestaticreadonlyList<(intXOffset,intYOffset)>Neighbors=new(){(-1,-1),(-1,0),(-1,1),(0,-1),(0,1),(1,-1),(1,0),(1,1)};

/// <summary>
/// Implements the flood fill algorithm through a breadth-first approach using a queue.
/// </summary>
/// <param name="bitmap">The bitmap to which the algorithm is applied.</param>
/// <param name="location">The start location on the bitmap.</param>
/// <param name="targetColor">The old color to be replaced.</param>
/// <param name="replacementColor">The new color to replace the old one.</param>
publicstaticvoidBreadthFirstSearch(SKBitmapbitmap,(intX,intY)location,SKColortargetColor,SKColorreplacementColor)
{
if(location.X<0||location.X>=bitmap.Width||location.Y<0||location.Y>=bitmap.Height)
{
thrownewArgumentOutOfRangeException(nameof(location),$"{nameof(location)} should point to a pixel within the bitmap");
}

varqueue=newList<(intX,intY)>();
queue.Add(location);

while(queue.Count>0)
{
BreadthFirstFill(bitmap,location,targetColor,replacementColor,queue);
}
}

/// <summary>
/// Implements the flood fill algorithm through a depth-first approach through recursion.
/// </summary>
/// <param name="bitmap">The bitmap to which the algorithm is applied.</param>
/// <param name="location">The start location on the bitmap.</param>
/// <param name="targetColor">The old color to be replaced.</param>
/// <param name="replacementColor">The new color to replace the old one.</param>
publicstaticvoidDepthFirstSearch(SKBitmapbitmap,(intX,intY)location,SKColortargetColor,SKColorreplacementColor)
{
if(location.X<0||location.X>=bitmap.Width||location.Y<0||location.Y>=bitmap.Height)
{
thrownewArgumentOutOfRangeException(nameof(location),$"{nameof(location)} should point to a pixel within the bitmap");
}

DepthFirstFill(bitmap,location,targetColor,replacementColor);
}

privatestaticvoidBreadthFirstFill(SKBitmapbitmap,(intX,intY)location,SKColortargetColor,SKColorreplacementColor,List<(intX,intY)>queue)
{
(intX,intY)currentLocation=queue[0];
queue.RemoveAt(0);

if(bitmap.GetPixel(currentLocation.X,currentLocation.Y)==targetColor)
{
bitmap.SetPixel(currentLocation.X,currentLocation.Y,replacementColor);

for(inti=0;i<Neighbors.Count;i++)
{
intx=currentLocation.X+Neighbors[i].XOffset;
inty=currentLocation.Y+Neighbors[i].YOffset;
if(x>=0&&x<bitmap.Width&&y>=0&&y<bitmap.Height)
{
queue.Add((x,y));
}
}
}
}

privatestaticvoidDepthFirstFill(SKBitmapbitmap,(intX,intY)location,SKColortargetColor,SKColorreplacementColor)
{
if(bitmap.GetPixel(location.X,location.Y)==targetColor)
{
bitmap.SetPixel(location.X,location.Y,replacementColor);

for(inti=0;i<Neighbors.Count;i++)
{
intx=location.X+Neighbors[i].XOffset;
inty=location.Y+Neighbors[i].YOffset;
if(x>=0&&x<bitmap.Width&&y>=0&&y<bitmap.Height)
{
DepthFirstFill(bitmap,(x,y),targetColor,replacementColor);
}
}
}
}
}