pica/lib/mm_resize/resize.js

High quality image resize in browser.

'use strict';


const createFilters        = require('./resize_filter_gen');
const { convolveHor, convolveVert, convolveHorWithPre, convolveVertWithPre } = require('./convolve');


function hasAlpha(src, width, height) {
  let ptr = 3, len = (width * height * 4)|0;
  while (ptr < len) {
    if (src[ptr] !== 255) return true;
    ptr = (ptr + 4)|0;
  }
  return false;
}

function resetAlpha(dst, width, height) {
  let ptr = 3, len = (width * height * 4)|0;
  while (ptr < len) { dst[ptr] = 0xFF; ptr = (ptr + 4)|0; }
}


module.exports = function resize(options) {
  const src   = options.src;
  const srcW  = options.width;
  const srcH  = options.height;
  const destW = options.toWidth;
  const destH = options.toHeight;
  const scaleX = options.scaleX || options.toWidth / options.width;
  const scaleY = options.scaleY || options.toHeight / options.height;
  const offsetX = options.offsetX || 0;
  const offsetY = options.offsetY || 0;
  const dest  = options.dest || new Uint8Array(destW * destH * 4);

  const filter = typeof options.filter === 'undefined' ? 'mks2013' : options.filter;
  const filtersX = createFilters(filter, srcW, destW, scaleX, offsetX),
        filtersY = createFilters(filter, srcH, destH, scaleY, offsetY);

  const tmp  = new Uint16Array(destW * srcH * 4);

  // Autodetect if alpha channel exists, and use appropriate method
  if (hasAlpha(src, srcW, srcH)) {
    convolveHorWithPre(src, tmp, srcW, srcH, destW, filtersX);
    convolveVertWithPre(tmp, dest, srcH, destW, destH, filtersY);
  } else {
    convolveHor(src, tmp, srcW, srcH, destW, filtersX);
    convolveVert(tmp, dest, srcH, destW, destH, filtersY);
    resetAlpha(dest, destW, destH);
  }

  return dest;
};