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Flood Fill

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/**
 * Flood fill.
 *
 * 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 https://www.techiedelight.com/flood-fill-algorithm/
 */

const neighborOffsets = [
  [-1, -1],
  [-1, 0],
  [-1, 1],
  [0, -1],
  [0, 1],
  [1, -1],
  [1, 0],
  [1, 1]
]

function isInside(rgbData, location) {
  const x = location[0]
  const y = location[1]
  return x >= 0 && x < rgbData.length && y >= 0 && y < rgbData[0].length
}

function checkLocation(rgbData, location) {
  if (!isInside(rgbData, location)) {
    throw new Error('location should point to a pixel within the rgbData')
  }
}

function* neighbors(rgbData, location) {
  for (const offset of neighborOffsets) {
    const neighborLocation = [location[0] + offset[0], location[1] + offset[1]]
    if (isInside(rgbData, neighborLocation)) {
      yield neighborLocation
    }
  }
}

/**
 * Implements the flood fill algorithm through a breadth-first approach using a queue.
 *
 * @param rgbData The image to which the algorithm is applied.
 * @param location The start location on the image.
 * @param targetColor The old color to be replaced.
 * @param replacementColor The new color to replace the old one.
 */
export function breadthFirstSearch(
  rgbData,
  location,
  targetColor,
  replacementColor
) {
  checkLocation(rgbData, location)

  const queue = []
  queue.push(location)

  while (queue.length > 0) {
    breadthFirstFill(rgbData, location, targetColor, replacementColor, queue)
  }
}

/**
 * Implements the flood fill algorithm through a depth-first approach using recursion.
 *
 * @param rgbData The image to which the algorithm is applied.
 * @param location The start location on the image.
 * @param targetColor The old color to be replaced.
 * @param replacementColor The new color to replace the old one.
 */
export function depthFirstSearch(
  rgbData,
  location,
  targetColor,
  replacementColor
) {
  checkLocation(rgbData, location)

  depthFirstFill(rgbData, location, targetColor, replacementColor)
}

/**
 * Utility-function to implement the breadth-first loop.
 *
 * @param rgbData The image to which the algorithm is applied.
 * @param location The start location on the image.
 * @param targetColor The old color to be replaced.
 * @param replacementColor The new color to replace the old one.
 * @param queue The locations that still need to be visited.
 */
function breadthFirstFill(
  rgbData,
  location,
  targetColor,
  replacementColor,
  queue
) {
  const currentLocation = queue[0]
  queue.shift()

  if (rgbData[currentLocation[0]][currentLocation[1]] === targetColor) {
    rgbData[currentLocation[0]][currentLocation[1]] = replacementColor
    for (const neighborLocation of neighbors(rgbData, currentLocation)) {
      queue.push(neighborLocation)
    }
  }
}

/**
 * Utility-function to implement the depth-first loop.
 *
 * @param rgbData The image to which the algorithm is applied.
 * @param location The start location on the image.
 * @param targetColor The old color to be replaced.
 * @param replacementColor The new color to replace the old one.
 */
function depthFirstFill(rgbData, location, targetColor, replacementColor) {
  if (rgbData[location[0]][location[1]] === targetColor) {
    rgbData[location[0]][location[1]] = replacementColor
    for (const neighborLocation of neighbors(rgbData, location)) {
      depthFirstFill(rgbData, neighborLocation, targetColor, replacementColor)
    }
  }
}