save_ui_to_bmp_electron_preload

gistfile1.txt

const fs = require('fs');
const Jimp = require('jimp');
const electron = require('electron');
const html2canvas = require('html2canvas');

const remote = electron.remote;
const nativeImage = electron.nativeImage

const Menu = remote.Menu;
const MenuItem = remote.MenuItem;

let rightClickPosition = null
const menu = new Menu();

menu.append(new MenuItem({
  label: 'Save Image',
  click: () => {
    html2canvas(printArea, {
      background: '#fff',
      onrendered: function(canvas) {
        saveCanvasAsBMP(canvas);
      }
    });
  }
}))

function saveCanvasAsBMP(canvas) {
  // canvas = contrastBlackWhiteCanvas(canvas, 150);
  const imgFilenameBmp = `${ Date.now() }.bmp`;
  const pngBuffer = nativeImage.createFromDataURL(
    canvas.toDataURL('image/png', 1)
  ).toPng();
  Jimp.read(pngBuffer, function (err, image) {
    if(err) { throw err }
    console.log(`Jimp read buffer success!`);
    image.write(imgFilenameBmp, function(err) {
      if(err) { throw err }
      console.log(`${imgFilenameBmp} save file success!`);
    });
  });
}

function contrastBlackWhiteCanvas(canvas, middle) {
  var
  context = canvas.getContext('2d'),
	imageData = context.getImageData(0, 0, canvas.width, canvas.height),
	canvasPixelArray = imageData.data,
	canvasPixelArrayLength = canvasPixelArray.length,
  i = 0;

	for (; i < canvasPixelArrayLength; i += 4) {
		canvasPixelArray[i] = canvasPixelArray[i] < middle ? 0 : 255;
		canvasPixelArray[i + 1] = canvasPixelArray[i + 1] < middle ? 0 : 255;
		canvasPixelArray[i + 2] = canvasPixelArray[i + 2] < middle ? 0 : 255;
	}

	context.putImageData(imageData, 0, 0);

	return canvas;
}

window.addEventListener('contextmenu', (e) => {
  e.preventDefault()
  rightClickPosition = {x: e.x, y: e.y}
  menu.popup(remote.getCurrentWindow())
}, false);

window.nodeRequire = require; 
delete window.require;
delete window.exports; delete window.module;