w8r / bresenham-zingl Goto Github PK

/* Extended from https://github.com/w8r/bresenham-zingl/blob/master/src/line.js */

module.exports.circle = (image, xm, ym, radius, outerColor, innerColor) => {
  const blendColor = (baseColor, addColor, x, y, alpha) => {
    /* eslint-disable no-bitwise */
    const baseB = (baseColor >> 24) & 0xff;
    const baseG = (baseColor >> 16) & 0xff;
    const baseR = (baseColor >> 8) & 0xff;
    const baseA = (baseColor & 0xff) / 255.0;

    const addB = (addColor >> 24) & 0xff;
    const addG = (addColor >> 16) & 0xff;
    const addR = (addColor >> 8) & 0xff;
    const addA = ((addColor & 0xff) / 255.0) * (1 - (alpha / 255.0));

    const a = 1 - ((1 - baseA) * (1 - addA));
    const r = Math.round(((addR * addA) / a) + ((baseR * baseA * (1 - addA)) / a));
    const g = Math.round(((addG * addA) / a) + ((baseG * baseA * (1 - addA)) / a));
    const b = Math.round(((addB * addA) / a) + ((baseB * baseA * (1 - addA)) / a));

    const color = Math.round(a * 255.0) | (r << 8) | (g << 16) | (b << 24);
    /* eslint-enable no-bitwise */
    image.setPixelColor(color, x, y);
  };
  let x = -radius;
  let y = 0;
  let i;
  let x2;
  let e2;
  let err = 2 - (2 * radius);
  const r = 1 - err;

  do {
    for (let j = xm + x; j <= xm - x; j += 1) {
      if (image.getPixelColor(j, ym - y) === 0) {
        image.setPixelColor(innerColor, j, ym - y);
      }
    }
    for (let j = xm - y; j <= xm + y; j += 1) {
      if (image.getPixelColor(j, ym - x) === 0) {
        image.setPixelColor(innerColor, j, ym - x);
      }
    }

    i = (255 * (err - (2 * (x + y)) - 2)) / r;
    blendColor(i > 0 ? 0x0 : innerColor, outerColor, xm - x, ym + y, Math.abs(i));
    blendColor(i > 0 ? 0x0 : innerColor, outerColor, xm - y, ym - x, Math.abs(i));
    blendColor(i > 0 ? 0x0 : innerColor, outerColor, xm + x, ym - y, Math.abs(i));
    blendColor(i > 0 ? 0x0 : innerColor, outerColor, xm + y, ym + x, Math.abs(i));

    e2 = err;
    x2 = x;
    if (err + y > 0) {
      i = (255 * (err - (2 * x) - 1)) / r;
      if (i < 256) {
        blendColor(0x0, outerColor, xm - x, ym + y + 1, i);
        blendColor(0x0, outerColor, xm - y - 1, ym - x, i);
        blendColor(0x0, outerColor, xm + x, ym - y - 1, i);
        blendColor(0x0, outerColor, xm + y + 1, ym + x, i);
      }
      x += 1;
      err += (x * 2) + 1;
    }
    if (e2 + x2 <= 0) {
      i = (255 * (((2 * y) + 3) - e2)) / r;
      if (i < 256) {
        blendColor(innerColor, outerColor, xm - x2 - 1, ym + y, i);
        blendColor(innerColor, outerColor, xm - y, ym - x2 - 1, i);
        blendColor(innerColor, outerColor, xm + x2 + 1, ym - y, i);
        blendColor(innerColor, outerColor, xm + y, ym + x2 + 1, i);
      }
      y += 1;
      err += (y * 2) + 1;
    }
  } while (x < 0);
};