mind-ar/src/image-target/utils/cumsum.js

web augmented reality framework

// fast 2D submatrix sum using cumulative sum algorithm
class Cumsum {
  constructor(data, width, height) {
    this.cumsum = [];
    for (let j = 0; j < height; j++) {
      this.cumsum.push([]);
      for (let i = 0; i < width; i++) {
        this.cumsum[j].push(0);
      }
    }

    this.cumsum[0][0] = data[0];
    for (let i = 1; i < width; i++) {
      this.cumsum[0][i] = this.cumsum[0][i-1] + data[i];
    }
    for (let j = 1; j < height; j++) {
      this.cumsum[j][0] = this.cumsum[j-1][0] + data[j*width];
    }

    for (let j = 1; j < height; j++) {
      for (let i = 1; i < width; i++) {
        this.cumsum[j][i] = data[j*width+i]
                               + this.cumsum[j-1][i]
                               + this.cumsum[j][i-1]
                               - this.cumsum[j-1][i-1];
      }
    }
  }

  query(x1, y1, x2, y2) {
    let ret = this.cumsum[y2][x2];
    if (y1 > 0) ret -= this.cumsum[y1-1][x2];
    if (x1 > 0) ret -= this.cumsum[y2][x1-1];
    if (x1 > 0 && y1 > 0) ret += this.cumsum[y1-1][x1-1];
    return ret;
  }
}

export {
  Cumsum
}