JSFiddle - React, Tailwind, and code Playground

by mgibsonbr

HTML

<script src="http://cdnjs.cloudflare.com/ajax/libs/camanjs/4.0.0/caman.full.min.js"></script>
<img id="id-imagem"...

JavaScript

var caman = Caman('#id-imagem', function()
    {
        this.render();
        canvas = this.canvas;
        ctx = this.context;
        init();
    });

var canvas, ctx,
rect = {},
drag = false;

function init() {
  canvas.addEventListener('mousedown', mouseDown, false);
  canvas.addEventListener('mouseup', mouseUp, false);
  canvas.addEventListener('mousemove', mouseMove, false);
}

function mouseDown(e) {
  rect.startX = e.pageX - this.offsetLeft;
  rect.startY = e.pageY - this.offsetTop;
  drag = true;
}

function mouseUp() {
  drag = false;
    caman.render();
    caman.crop(rect.w, rect.h, rect.startX, rect.startY);
    caman.render();
}

function mouseMove(e) {
  if (drag) {
    rect.w = (e.pageX - this.offsetLeft) - rect.startX;
    rect.h = (e.pageY - this.offsetTop) - rect.startY ;
    //ctx.clearRect(0,0,canvas.width,canvas.height); // Não é necessário
    draw();
  }
}

function draw() {
  caman.render(function() {
      ctx.fillStyle = "rgba(0, 0, 255, 0.4)";
      ctx.fillRect(rect.startX, rect.startY, rect.w, rect.h);
  });
}