mt-polygon-simplification/lib/wasm-util/coordinates.js

/*
 Utility functions to store and load coordinates to and from module memory
 Coordinates are assumed to be an array of coordinate pairs ([[x1,y1], [x2,y2], [x3,y3]])
*/

/**
 * Allocate memory for coordinates and stores them in a flat representation.
 * Returns a pointer to the buffer. The length of the buffer is coords.length * 2
 * @param {*} module
 * @param {Array} coords - An array of coordinate pairs
 */
export function storeCoords(module, coords) {
  const flatSize = coords.length * 2
  const offset = module._malloc(flatSize * Float64Array.BYTES_PER_ELEMENT)
  const heapView = new Float64Array(module.HEAPF64.buffer, offset, flatSize)
  for (let i = 0; i < coords.length; i++) {
    heapView[2 * i] = coords[i][0]
    heapView[2 * i + 1] = coords[i][1]
  }
  return offset
}

/**
 * Loads coordinates from the memory by the result pointer.
 * Frees the resultpointer and the result before returning
 * @param {*} module
 * @param {*} result - pointer to Uint32 array of length 2. Stores the resultPointer and resultLength
 */
export function loadResultAndFreeMemory(module, resultInfo) {
  const [resultPointer, resultLength] = new Uint32Array(
    module.HEAPU32.buffer,
    resultInfo,
    2
  )
  const simplified = new Float64Array(
    module.HEAPF64.buffer,
    resultPointer,
    resultLength
  )
  const coords = unflattenCoords(simplified)
  module._free(resultInfo)
  module._free(resultPointer)
  return coords
}

/**
 * Loads coordinates from the memory by the result pointer without freeing memory.
 * For benchmarking purposes
 * @param {*} module
 * @param {*} result - pointer to Uint32 array of length 2. Stores the resultPointer and resultLength
 */
export function loadResult(module, result) {
  const [resultPointer, resultLength] = new Uint32Array(
    module.HEAPU32.buffer,
    result,
    2
  )
  const simplified = new Float64Array(
    module.HEAPF64.buffer,
    resultPointer,
    resultLength
  )
  return unflattenCoords(simplified)
}

/**
 * Transforms a flat array to an array coordinate pairs
 * @param {Array} flattened - length must be even
 */
export function unflattenCoords(flattened) {
  const coords = []
  let x, y
  for (let i = 0; i < flattened.length; i += 2) {
    x = flattened[i]
    y = flattened[i + 1]
    coords.push([x, y])
  }
  return coords
}