HTML5 Canvas Javascript how to make smooth brush

Question

Hello i need make smooth brush likes this:

I try to create it, i make circle and fill it, but result not successful:

Can be seen circles.. this is not smooth like first example my example code:

function distanceBetween(point1, point2) {
  return Math.sqrt(Math.pow(point2.x - point1.x, 2) + Math.pow(point2.y - point1.y, 2));
}
function angleBetween(point1, point2) {
  return Math.atan2( point2.x - point1.x, point2.y - point1.y );
}

var el = document.getElementById('c');
var ctx = el.getContext('2d');

//ctx.fillStyle = "rgba('255, 0, 0, 0.1')";
ctx.fillStyle = "red";
ctx.strokeStyle = "red";
ctx.globalAlpha = "0.05";
ctx.lineWidth = 0;
ctx.globalCompositeOperation = "source-over"; 

var isDrawing, lastPoint;

el.onmousedown = function(e) {
  isDrawing = true;
  lastPoint = { x: e.clientX, y: e.clientY };
};

el.onmousemove = function(e) {
  if (!isDrawing) return;
  
  var currentPoint = { x: e.clientX, y: e.clientY };
  var dist = distanceBetween(lastPoint, currentPoint);
  var angle = angleBetween(lastPoint, currentPoint);
  
  for (var i = 0; i < dist; i+=5) {
    x = lastPoint.x + (Math.sin(angle) * i) - 25;
    y = lastPoint.y + (Math.cos(angle) * i) - 25;
    ctx.beginPath();
    ctx.arc(x+10, y+10, 20, false, Math.PI * 2, false);
    ctx.closePath();
    ctx.fill();
    ctx.stroke();
  }
  
  lastPoint = currentPoint;
};

el.onmouseup = function() {
  isDrawing = false;
};

function clearit() {
  ctx.clearRect(0,0, 1000, 1000);
}

canvas { border: 1px solid #ccc }

<canvas id="c" width="500" height="300"></canvas>
<input type="button" id="clear-btn" value="Clear it" onclick="clearit()">

http://codepen.io/anon/pen/NPjwry

Answer 1

Try with a smaller globalAlpha and decrease the stepping (so you draw more circles)

function distanceBetween(point1, point2) {
  return Math.sqrt(Math.pow(point2.x - point1.x, 2) + Math.pow(point2.y - point1.y, 2));
}
function angleBetween(point1, point2) {
  return Math.atan2( point2.x - point1.x, point2.y - point1.y );
}

var el = document.getElementById('c');
var ctx = el.getContext('2d');

//ctx.fillStyle = "rgba('255, 0, 0, 0.1')";
ctx.fillStyle = "red";
ctx.strokeStyle = "red";
ctx.globalAlpha = "0.01";
ctx.lineWidth = 0;
ctx.globalCompositeOperation = "source-over"; 

var isDrawing, lastPoint;

el.onmousedown = function(e) {
  isDrawing = true;
  lastPoint = { x: e.clientX, y: e.clientY };
};

el.onmousemove = function(e) {
  if (!isDrawing) return;
  
  var currentPoint = { x: e.clientX, y: e.clientY };
  var dist = distanceBetween(lastPoint, currentPoint);
  var angle = angleBetween(lastPoint, currentPoint);
  
  for (var i = 0; i < dist; i+=3) {
    x = lastPoint.x + (Math.sin(angle) * i) - 25;
    y = lastPoint.y + (Math.cos(angle) * i) - 25;
    ctx.beginPath();
    ctx.arc(x+10, y+10, 20, false, Math.PI * 2, false);
    ctx.closePath();
    ctx.fill();
    ctx.stroke();
  }
  
  lastPoint = currentPoint;
};

el.onmouseup = function() {
  isDrawing = false;
};

function clearit() {
  ctx.clearRect(0,0, 1000, 1000);
}

canvas { border: 1px solid #ccc }

<canvas id="c" width="500" height="300"></canvas>
<input type="button" id="clear-btn" value="Clear it" onclick="clearit()">

Updated codepen: http://codepen.io/gpetrioli/pen/ramqBz