FloodFill.js

/**
 * 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/).
 */

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

const black = [0, 0, 0]
const green = [0, 255, 0]
const violet = [255, 0, 255]
const white = [255, 255, 255]
const orange = [255, 128, 0] // eslint-disable-line

/*
Doctests
> testBreadthFirst([1, 1], green, orange, [1, 1]);
orange
> testBreadthFirst([1, 1], green, orange, [0, 1]);
violet
> testBreadthFirst([1, 1], green, orange, [6, 4]);
white
> testDepthFirst([1, 1], green, orange, [1, 1]);
orange
> testDepthFirst([1, 1], green, orange, [0, 1]);
violet
> testDepthFirst([1, 1], green, orange, [6, 4]);
white
*/

/**
* 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.
*/
function breadthFirstSearch (rgbData, location, targetColor, replacementColor) {
  if (location[0] < 0 ||
    location[0] >= rgbData.length ||
    location[1] < 0 ||
    location[1] >= rgbData[0].length) {
    throw new Error('location should point to a pixel within the rgbData')
  }

  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.
*/
function depthFirstSearch (rgbData, location, targetColor, replacementColor) {
  if (location[0] < 0 ||
    location[0] >= rgbData.length ||
    location[1] < 0 ||
    location[1] >= rgbData[0].length) {
    throw new Error('location should point to a pixel within the rgbData')
  }

  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 (let i = 0; i < neighbors.length; i++) {
      const x = currentLocation[0] + neighbors[i][0]
      const y = currentLocation[1] + neighbors[i][1]
      if (x >= 0 && x < rgbData.length && y >= 0 && y < rgbData[0].length) {
        queue.push([x, y])
      }
    }
  }
}

/**
* 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 (let i = 0; i < neighbors.length; i++) {
      const x = location[0] + neighbors[i][0]
      const y = location[1] + neighbors[i][1]
      if (x >= 0 && x < rgbData.length && y >= 0 && y < rgbData[0].length) {
        depthFirstFill(rgbData, [x, y], targetColor, replacementColor)
      }
    }
  }
}

/**
* Generates the rgbData-matrix for the tests
*
* @return example rgbData-matrix
*/
function generateTestRgbData () {
  const layout = [
    [violet, violet, green, green, black, green, green],
    [violet, green, green, black, green, green, green],
    [green, green, green, black, green, green, green],
    [black, black, green, black, white, white, green],
    [violet, violet, black, violet, violet, white, white],
    [green, green, green, violet, violet, violet, violet],
    [violet, violet, violet, violet, violet, violet, violet]
  ]

  // transpose layout-matrix so the x-index comes before the y-index
  const transposed = []
  for (let x = 0; x < layout[0].length; x++) {
    transposed[x] = []
    for (let y = 0; y < layout.length; y++) {
      transposed[x][y] = layout[y][x]
    }
  }

  return transposed
}

/**
* Utility-function to test the function "breadthFirstSearch"
*
* @param fillLocation The start location on the image where the flood fill is applied.
* @param targetColor The old color to be replaced.
* @param replacementColor The new color to replace the old one.
* @param testLocation The location of the color to be checked.
* @return The color at testLocation
*/
function testBreadthFirst (fillLocation, targetColor, replacementColor, testLocation) {// eslint-disable-line
  const rgbData = generateTestRgbData()
  breadthFirstSearch(rgbData, fillLocation, targetColor, replacementColor)
  return rgbData[testLocation[0]][testLocation[1]]
}

/**
* Utility-function to test the function "depthFirstSearch"
*
* @param fillLocation The start location on the image where the flood fill is applied.
* @param targetColor The old color to be replaced.
* @param replacementColor The new color to replace the old one.
* @param testLocation The location of the color to be checked.
* @return The color at testLocation
*/
function testDepthFirst (fillLocation, targetColor, replacementColor, testLocation) {// eslint-disable-line
  const rgbData = generateTestRgbData()
  depthFirstSearch(rgbData, fillLocation, targetColor, replacementColor)
  return rgbData[testLocation[0]][testLocation[1]]
}