Создадим ещё одну кисть, теперь уже с эффектом кривой Безье, для созданной нами ранее paint программы.

HTML

<div class="container">
    <div class="column1">
        <canvas id="color" width="500" height="128"></canvas>
    </div>
    <div class="column2">
        <div>Предпросмотр:</div>
        <div id="preview"></div>
        <div id="pick"></div>
    </div>
    <div style="clear:both;"></div>
</div>
<canvas id="panel" width="1000" height="600"></canvas>

CSS

/* page layout styles */
*{
    margin:0;
    padding:0;
}
body {
    background-color:#eee;
    color:#fff;
    font:14px/1.3 Arial,sans-serif;
}
.container {
    color: #000;
    margin: 20px auto;
    overflow: hidden;
    position: relative;
    width: 800px;
}
/* custom styles */
.column1 {
    float:left;
    width:500px;
}
.column2 {
    float:left;
    padding-left:20px;
    width:170px;
}
#panel {
    border:1px #000 solid;
    box-shadow:4px 6px 6px #444444;
    cursor:crosshair;
    display:block;
    margin:0 auto;
    height:600px;
    width:1000px;
}
#color {
    border:1px #000 solid;
    box-shadow:0px 4px 6px #444444;
    cursor:crosshair;
}
.column2 > div {
    margin-bottom:10px;
}
#preview, #pick {
    border:1px #000 solid;
    box-shadow:2px 3px 3px #444444;
    height:40px;
    width:80px;
    border-radius:3px;
    -moz-border-radius:3px;
    -webkit-border-radius:3px;
}

jаvascript

Похожий код, только добавлена новая кисть:

var canvas;
var canvasColor;
var ctx;
var ctxColor;
var bMouseDown = false;
var selColorR = 0;
var selColorG = 0;
var selColorB = 0;
var BezierCurveBrush = {
    // inner variables
    iPrevX : 0,
    iPrevY : 0,
    points : null,
    // initialization function
    init: function () { },
    startCurve: function (x, y) {
        this.iPrevX = x;
        this.iPrevY = y;
        this.points = new Array();
    },
    getPoint: function (iLength, a) {
        var index = a.length - iLength, i;
        for (i=index; i< a.length; i++) {
            if (a[i]) {
                return a[i];
            }
        }
    },
    draw: function (x, y) {
        if (Math.abs(this.iPrevX - x) > 5 || Math.abs(this.iPrevY - y) > 5) {
            this.points.push([x, y]);
            // draw main path stroke
            ctx.beginPath();
            ctx.moveTo(this.iPrevX, this.iPrevY);
            ctx.lineTo(x, y);
            ctx.lineWidth = 1;
            ctx.strokeStyle = 'rgba(' + selColorR + ', ' + selColorG + ', ' + selColorB + ', 0.9)';
            ctx.stroke();
            ctx.closePath();
            // draw extra strokes
            ctx.strokeStyle = 'rgba(' + selColorR + ', ' + selColorG + ', ' + selColorB + ', 0.2)';
            ctx.beginPath();
            var iStartPoint = this.getPoint(25, this.points);
            var iFirstPoint = this.getPoint(1, this.points);
            var iSecondPoint = this.getPoint(5, this.points);
            ctx.moveTo(iStartPoint[0],iStartPoint[1]);
            ctx.bezierCurveTo(iFirstPoint[0], iFirstPoint[1], iSecondPoint[0], iSecondPoint[1], x, y);
            ctx.stroke();
            ctx.closePath();
            this.iPrevX = x;
            this.iPrevY = y;
        }
    }
};
$(function(){
    // creating canvas objects
    canvas = document.getElementById('panel');
    ctx = canvas.getContext('2d');
    canvasColor = document.getElementById('color');
    ctxColor = canvasColor.getContext('2d');
    drawGradients(ctxColor);
    BezierCurveBrush.init();
    $('#color').mousemove(function(e) { // mouse move handler
        var canvasOffset = $(canvasColor).offset();
        var canvasX = Math.floor(e.pageX - canvasOffset.left);
        var canvasY = Math.floor(e.pageY - canvasOffset.top);
        var imageData = ctxColor.getImageData(canvasX, canvasY, 1, 1);
        var pixel = imageData.data;
        var pixelColor = 'rgba('+pixel[0]+', '+pixel[1]+', '+pixel[2]+', '+pixel[3]+')';
        $('#preview').css('backgroundColor', pixelColor);
    });
    $('#color').click(function(e) { // mouse click handler
        var canvasOffset = $(canvasColor).offset();
        var canvasX = Math.floor(e.pageX - canvasOffset.left);
        var canvasY = Math.floor(e.pageY - canvasOffset.top);
        var imageData = ctxColor.getImageData(canvasX, canvasY, 1, 1);
        var pixel = imageData.data;
        var pixelColor = 'rgba('+pixel[0]+', '+pixel[1]+', '+pixel[2]+', '+pixel[3]+')';
        $('#pick').css('backgroundColor', pixelColor);
        selColorR = pixel[0];
        selColorG = pixel[1];
        selColorB = pixel[2];
    }); 
    $('#panel').mousedown(function(e) { // mouse down handler
        bMouseDown = true;
        var canvasOffset = $(canvas).offset();
        var canvasX = Math.floor(e.pageX - canvasOffset.left);
        var canvasY = Math.floor(e.pageY - canvasOffset.top);
        BezierCurveBrush.startCurve(canvasX, canvasY, false, false, false, false, false, false, canvasX, canvasY, 0, 0);
    });
    $('#panel').mouseup(function(e) { // mouse up handler
        bMouseDown = false;
    });
    $('#panel').mousemove(function(e) { // mouse move handler
        if (bMouseDown) {
            var canvasOffset = $(canvas).offset();
            var canvasX = Math.floor(e.pageX - canvasOffset.left);
            var canvasY = Math.floor(e.pageY - canvasOffset.top);
            BezierCurveBrush.draw(canvasX, canvasY, false, false, false, false, false, false, canvasX, canvasY, 0, 0);
        }
    });
});
function drawGradients() {
    var grad = ctxColor.createLinearGradient(20, 0, canvasColor.width - 20, 0);
    grad.addColorStop(0, 'red');
    grad.addColorStop(1 / 6, 'orange');
    grad.addColorStop(2 / 6, 'yellow');
    grad.addColorStop(3 / 6, 'green')
    grad.addColorStop(4 / 6, 'aqua');
    grad.addColorStop(5 / 6, 'blue');
    grad.addColorStop(1, 'purple');
    ctxColor.fillStyle=grad;
    ctxColor.fillRect(0, 0, canvasColor.width, canvasColor.height);
}