HTML5 canvas – Custom brush (BezierCurveBrush)

Andrey Prikaznov

Dec. 27, 11 · Web Dev Zone · Interview

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I hope that you still remember when we did our first Paint program with HTML5. Today I have decided to enhance it by adding new additional brush to it. This brush will use ‘bezierCurveTo’ function. As a result we will have an interesting effect; just check out it!

Here are our demo and downloadable package:

Live Demo

download in package

Ok, download the source files and lets start coding !

Step 1. HTML

Here is the html code for our enhanced Paint:

index.html

<!DOCTYPE html>
<html lang="en" >
    <head>
        <meta charset="utf-8" />
        <title>HTML5 canvas - Custom brush (BezierCurveBrush) for your paing program | Script Tutorials</title>
        <link href="css/main.css" rel="stylesheet" type="text/css" />

        <script src="js/jquery-1.5.2.min.js"></script>
        <script src="js/script.js"></script>
    </head>
    <body>
        <header>
            <h2>HTML5 canvas - Custom brush (BezierCurveBrush) for your paing program</h2>
            <a href="http://www.script-tutorials.com/html5-canvas-custom-brush1/" class="stuts">Back to original tutorial on <span>Script Tutorials</span></a>
        </header>
        <div class="container">
            <div class="column1">
                <canvas id="color" width="500" height="128"></canvas>
            </div>
            <div class="column2">
                <div>Preview:</div>
                <div id="preview"></div>
                <div id="pick"></div>
            </div>
            <div style="clear:both;"></div>
        </div>
        <canvas id="panel" width="1000" height="600"></canvas>
    </body>
</html>

Step 2. CSS

Here are the CSS styles used:

css/main.css

/* page layout styles */
*{
    margin:0;
    padding:0;
}
body {
    background-color:#eee;
    color:#fff;
    font:14px/1.3 Arial,sans-serif;
}
header {
    background-color:#212121;
    box-shadow: 0 -1px 2px #111111;
    display:block;
    height:70px;
    position:relative;
    width:100%;
    z-index:100;
}
header h2{
    font-size:22px;
    font-weight:normal;
    left:50%;
    margin-left:-400px;
    padding:22px 0;
    position:absolute;
    width:540px;
}
header a.stuts,a.stuts:visited{
    border:none;
    text-decoration:none;
    color:#fcfcfc;
    font-size:14px;
    left:50%;
    line-height:31px;
    margin:23px 0 0 110px;
    position:absolute;
    top:0;
}
header .stuts span {
    font-size:22px;
    font-weight:bold;
    margin-left:5px;
}
.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;
}

Step 3. JS

js/script.js

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);
}

What I have added here – BezierCurveBrush object. This is a pretty easy object, with its own Draw function where we use ‘bezierCurveTo’ function to draw curves between the first point (in the beginning of drawing) and all next stored points.

Live Demo

download in package

Conclusion

Hope that today’s lesson was interesting for you. I will be glad to see your thanks and comments. Good luck!

Source: http://www.script-tutorials.com/html5-canvas-custom-brush1/

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HTML5 canvas – Custom brush (BezierCurveBrush)

Live Demo

download in package

Step 1. HTML

index.html

Step 2. CSS

css/main.css

Step 3. JS

js/script.js

Live Demo

download in package

Conclusion

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