Canvas: Insert fading rectangle between drawn image and clip - javascript

I am trying to create a rectangle which will fade on top of an image that is being clipped dynamically.
However any instance of creating a rectangle goes behind the drawn image, and I can't seem to figure out how to place it on top so both the shape and image become clipped.
Here is a Fiddle of where I am currently: JSFiddle
Here is my html:
<div id='demo'>
<canvas id="canvas" width="200px" height="200px"></canvas>
<img id="img" src="http://www.filterforge.com/more/help/images/size200.jpg" />
</div>
Here is my javascript:
function init(){
var canvas = document.getElementById('canvas');
var c = canvas.getContext('2d');
var r = 1;
function draw(){
c.beginPath();
c.arc(100,100,r,0,2*Math.PI,false);
r = r + 1;
// Start Image
c.save();
c.clip();
var img = document.getElementById('img');
c.drawImage(img,0,0);
c.restore();
// The Rectangle I am also trying to mask
c.fillStyle = "rgba(0,0,0,0.025)"
c.fillRect(0, 0, 200, 200);
c.save();
c.clip();
c.restore();
if(r < 100){
requestAnimationFrame(draw);
}
r++;
}
requestAnimationFrame(draw);
}
init();
I would appreciate any help you guys can offer.
Thanks,

Here's the order you want for your clipping:
context.save
define the clipping region (eg your arc)
drawImage
context.restore
Demo: http://jsfiddle.net/m1erickson/YS45U/
Code:
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas = document.getElementById('canvas');
var c = canvas.getContext('2d');
var r = 0;
var img=new Image();
img.onload=function(){
draw();
};
img.src="http://www.filterforge.com/more/help/images/size200.jpg";
function draw(){
// request another animation if not 100%
if(++r<100){
requestAnimationFrame(draw);
}
// save the unclipped context
c.save();
// set the clipping region
c.beginPath();
c.arc(100,100,r,0,2*Math.PI,false);
c.closePath();
c.clip();
// draw the image into the clipped region
c.drawImage(img,0,0);
// restore the canvas context
c.restore();
}
$("#stop").click(function(){});
}); // end $(function(){});
</script>
</head>
<body>
<button id="stop">Stop</button><br>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>

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Rotate html5 canvas text from its center point

I want to rotate the HTML5 canvas text with dynamic X, Y value from it's center position. I used the below code as mentioned in the stackoverflow link HTML5 rotate text around it's centre point . but text is always rotating from start point. I need from center point rotation. This is my code.
this.ctx.textAlign = "center";
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Thanks,
Bharathiraja.
Your code is working: http://jsfiddle.net/m1erickson/d40xr8nL/
If its not working on your end:
be sure your options properties are valid.
wrap the code in ctx.save & ctx.restore (because transforms are cumulative).
Example code:
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var x=150;
var y=150;
var labelRotation=45;
var label="This is some text.";
animate();
function draw(){
ctx.clearRect(0,0,canvas.width,canvas.height);
//
ctx.beginPath();
ctx.arc(x,y,3,0,Math.PI*2);
ctx.closePath();
ctx.fill();
//
ctx.save();
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.translate(x , y);
ctx.rotate(labelRotation * Math.PI / 180);
ctx.fillText(label, 0, 0);
ctx.restore();
}
function animate(){
requestAnimationFrame(animate);
labelRotation++;
draw();
}
}); // end $(function(){});
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Highlight area of image with canvas/JS

I am trying to alter an image by highlighting an area defined by coordinates.
I've been using two canvases, on top of each other. Now I don't know if this is the best way to do it in the first place. http://jsfiddle.net/9wJu8/
<canvas id='canvas'>Your browser does not support HTML5 canvas</canvas>
<canvas id='canvas2'>Your browser does not support HTML5 canvas</canvas>
Currently, I am using two images, but I wonder if there is any way to use masks on canvas.
Second of all, I'd like to save the output of the stacked canvases.
What #Ken said but I think some of his code example was accidentally omitted:
A Demo: http://jsfiddle.net/m1erickson/Spkhz/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=700;
var ch=438;
var img=new Image();
img.onload=start;
img.src="cat.jpg";
function start(){
canvas.width=cw;
canvas.height=ch;
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ctx.drawImage(img,0,0,cw,ch);
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ctx.save();
ctx.globalAlpha=.50;
ctx.fillStyle="black";
ctx.fillRect(0,0,cw,ch);
ctx.restore();
// ctx.clip() the area to highlight
// and redraw the whole image
// (the image will draw only in the clipping region)
ctx.save();
ctx.beginPath();
ctx.clearRect(300,100,200,100);
ctx.rect(300,100,200,100);
ctx.clip();
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ctx.restore();
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}); // end $(function(){});
</script>
</head>
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<canvas id="canvas" width=300 height=300></canvas>
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</html>
You can use a single canvas for this:
➔ Draw complete image
➔ Draw a transparent black rectangle on top
➔ Use drawImage() with clipping settings
For example:
// draw full image
ctx.drawImage(img, 0, 0);
// cover with a darkened overlay
ctx.fillStyle = 'rgba(0,0,0, 0.5);
ctx.fillRect(0, 0, canvas.width, canvas.height);
// draw region of image
ctx.drawImage(img, x, y, w, h, x, y, w, h);
where x, y, w and h is the region you want to highlight.
To save out as an image just use toDataURL() on the canvas element.

Click image to add to HTML5 Canvas path

I am drawing a circle onto my html5 canvas like below:
<!DOCTYPE HTML>
<html>
<head>
<style>
body {
margin: 0px;
padding: 0px;
}
</style>
</head>
<body>
<canvas id="myCanvas" width="578" height="200"></canvas>
<script>
var canvas = document.getElementById('myCanvas');
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below is the image of what i'm asking:
circular drag http://www.papiobeads.com/images/theimage.png
You can use canvas transformations to rotate your image around the circumference of your circle.
Move to your desired rotation point (the center of your circle)
Set your desired rotation angle (in radians)
Draw the image
Here's example code and a Demo: http://jsfiddle.net/m1erickson/t5N9T/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" />
<script src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var radianAngle=0;
var cx=150;
var cy=150;
var radius=50;
var img=new Image();img.onload=start;img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/cars.png";
function start(){
animate();
}
function animate() {
requestAnimationFrame(animate);
// Drawing code goes here
radianAngle+=Math.PI/120;
ctx.clearRect(0,0,canvas.width,canvas.height);
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ctx.beginPath();
ctx.arc(cx,cy,radius,0,Math.PI*2);
ctx.closePath();
ctx.stroke();
// draw the image rotated around the circumference
ctx.save();
ctx.translate(cx,cy);
ctx.rotate(radianAngle);
ctx.drawImage(img,radius-img.width/2,-img.height/2);
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I am trying to draw an arc within a canvas and i want to make that arc to fill the canvas.
i tried to make the arc half canvas's size and i works perfectly but when i increase the radius to be same width as the canvas i find an error...as for arc width its good but for the height it increases alot, disappears and i feel like radius is doubling the y-axis.
and when i check it in jsFiddle it works perfectly...maybe i have to do with some css or something?
var canvas = document.getElementById("canvas2");
var context = canvas.getContext("2d");
var counterClockwise = false;
var x = canvas.width /2;
var y = canvas.height /2;
context.beginPath();
context.arc(x, y, x-9, 0, 2*Math.PI);
context.stroke();
and this the html body:
<!DOCTYPE html>
<html>
<head>
<link type="text/css" rel="stylesheet" href="css/font-awesome.css" />
</head>
<body>
<canvas id="canvas2" style="width:207px;height:207px"></canvas>
</body>
</html>
Set the width and height on the canvas element itself, not in CSS:
canvas.width=207;
canvas.height=207;
Setting width and height in css will distort your drawings (as you've discovered).
Also, when you draw an arc which you intend to be a circle, be sure to call context.closePath();
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/adGfS/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas = document.getElementById("canvas2");
var context = canvas.getContext("2d");
canvas.width=207;
canvas.height=207;
var x = canvas2.width /2;
var y = canvas2.height /2;
context.beginPath();
context.arc(x, y, x-9, 0, 2*Math.PI);
context.closePath();
context.stroke();
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas2"></canvas>
</body>
</html>

Display whole image in circulr shape using Javascript or HTML5

How can I display whole image in circulr shape using Javascript or HTML5. I tried the code below but with this code only part of the image will be converted into circular shape. How can I make the whole display in circular shape?
<!DOCTYPE HTML>
<html>
<head>
<style>
body {
margin: 0px;
padding: 0px;
}
#myCanvas {
border: 1px solid #9C9898;
}
</style>
<script type="text/javascript" >
</script>
</head>
<body>
<canvas id="myCanvas" width="578" height="200"></canvas>
<div id="myCanvas"></div>
<script>
var ctx = document.getElementById('myCanvas').getContext("2d");
ctx.arc(100,100, 50, 0, Math.PI*2,true); // you can use any shape
ctx.clip();
var img = new Image();
img.addEventListener('load', function(e) {
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img.src="images/hospital_review_profile_placeholder.png";
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Instead of using ctx.clip(), you would resize and reposition your image to fit in your circle.
Here is code that will resize your image to its largest size that will fit in the circle.
Then the code positions the resized image properly in the circle.
Here is a Fiddle --- http://jsfiddle.net/m1erickson/s6MzZ/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
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var fullWidth=200; // actual width of image in pixels
var fullHeight=300; // actual height of image in pixels
var centerX=100; // center X coordinate of the circle
var centerY=100; // center Y coordinate of the Circle
// the image must be resized to fit into the circle
// Call CalcResizedImageDimensions() to get the resized width/height
var size=CalcResizedImageDimensions(radius,fullWidth,fullHeight);
var rectX=centerX-size.width/2; // the X coordinate of the resized rectangle
var rectY=centerY-size.height/2 // the Y coordinate of the resized rectangle
ctx.beginPath();
ctx.arc(centerX,centerY,radius,0,Math.PI*2,true);
// I illustrate with just a rectangle
// you would drawImage() instead
ctx.rect(rectX,rectY,size.width,size.height);
ctx.stroke();
function CalcResizedImageDimensions(r,w,h){
var d=2*r;
var newH=(d*h)/Math.sqrt(w*w+h*h);
var newW=w/h*newH;
return({width:newW,height:newH});
}
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=200 height=200></canvas>
</body>
</html>

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