I am trying to add some animation on changing the endAngle of a canvas arc like this but it is not working. How can I do this?
var steps =30;
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 75;
var startAngle = 1.5 * Math.PI;
var endAngle = 1.4999 * Math.PI;
var counterClockwise = false;
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.lineWidth = 15;
context.strokeStyle = 'black';
context.stroke();
setTimeout(function(){
endAngle = endAngle - 1;
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.stroke();
}, 1000);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="myCanvas" width="250" height="250"></canvas>
new answer
Whenever you draw something on the canvas it doesn't erase what was previously drawn on it. You have to do that manually like this:
context.fillStyle="#ffffff";
context.fillRect(0,0,250,250);
//draw here
full solution:
<html>
<body>
<canvas id="myCanvas" width="250" height="250"></canvas>
<script language=javascript>
var steps =30;
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 75;
var startAngle = 1.5 * Math.PI;
var endAngle = 1.49 * Math.PI;
var counterClockwise = false;
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.lineWidth = 15;
context.strokeStyle = 'black';
context.stroke();
setInterval(function(){
context.fillStyle="#ffffff";
context.fillRect(0,0,250,250);
endAngle = endAngle - 0.01;
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.stroke();
}, 10);
</script>
</body>
</html>
old answer
Well there are a few things. You've got your clockwise and counterclockwise mixed up causing the circle to be completely full before your "animation" starts.
if you want it clockwise then put the end angle ahead like this:
var startAngle = 1.5 * Math.PI;
var endAngle = 1.51 * Math.PI;
And then increase the angle in your animation timeout instead of decrease:
endAngle = endAngle+1;
and finally, your timeout should be an interval, not a timeout. The timeout will only run once. simple as changing it to
setInterval(function(){...
You also don't need jquery for this code by the way.
Related
I've been learning some javascript/canvas animation, I'm having trouble getting this animation to work correctly.
My goal is that the animation will start drawing at the top, then as it gets back to the top it will stop progressing and the start position will progress around the arc making it look as though it is erasing itself and once at the top (1.5 * PI) will starting drawing again.
Here is a fiddle: https://jsfiddle.net/kg1fmsjj/
Here is my code:
function f(element, colour, thickness, elapsedTime) {
// Create Element
element.innerHTML = '';
var canvas = document.createElement('canvas');
var context = canvas.getContext("2d");
element.appendChild(canvas);
// Circle Params
context.lineWidth = thickness;
context.strokeStyle = colour;
var width = canvas.width;
var height = canvas.height;
var mathPi = Math.PI;
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 40;
var startAngle = 1.5 * mathPi;
var endAngle = 1.5 * mathPi;
context.lineWidth = thickness;
context.strokeStyle = colour;
var erasing = false;
function animate() {
if(erasing) {
startAngle = startAngle + 0.01 * mathPi;
} else {
endAngle = endAngle + 0.01 * mathPi;
}
if (endAngle > (1.5 * mathPi)) {
erasing = true;
}
if (startAngle > (1.5 * mathPi)) {
erasing = false;
}
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, false);
context.stroke();
context.closePath();
}
setInterval(animate, 10);
}
f(document.getElementById('out'), '#800080', 4, 60);
context.arc lets you optionally draw your arc counterclockwise.
This ability lets you create your desired effect:
To "draw" the arc, draw an increasing arc clockwise.
To "erase" the arc, draw a decreasing arc counterclockwise.
Here's example code and a Demo:
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
ctx.lineWidth=2;
ctx.strokeStyle='#800080';
var PI=Math.PI;
var cx=cw/2;
var cy=ch/2;
var radius=cw/2-30;
var angle=0;
var direction=1;
requestAnimationFrame(animate);
function animate(time){
ctx.clearRect(0,0,cw,ch);
angle+=PI/120;
if(angle<0 || angle>PI*2){
angle=0;
direction*=-1;
}
draw();
requestAnimationFrame(animate);
}
function draw(){
var counterclockwise=(direction>0)?false:true;
var s=-Math.PI/2;
var e=angle-Math.PI/2;
ctx.beginPath();
ctx.arc(cx,cy,radius,s,e,counterclockwise);
ctx.stroke();
}
body{ background-color: ivory; }
#canvas{border:1px solid red; margin:0 auto; }
<canvas id="canvas" width=300 height=300></canvas>
You need to clear the canvas on each repaint using the clearRect() method.
You need to change the conditions when erasing variable is toggled. If erasing and startAngle >= endAngle then toggle erasing variable. If not erasing and endAngle >= startAngle + 2 * PI then toggle erasing variable.
The animate() method then become...
function animate() {
if(erasing) {
startAngle = startAngle + 0.01 * mathPi;
if (startAngle >= endAngle) {
erasing = false;
}
} else {
endAngle = endAngle + 0.01 * mathPi;
if (endAngle >= startAngle + 2.0 * mathPi) {
erasing = true;
}
}
context.clearRect(0, 0, canvas.width, canvas.height);
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, false);
context.stroke();
}
I want to draw a shape like this using html5 canvas
but I don't want to use curves.
is there any way to draw it using arc function ?
or at least how can I draw a curve exactly like when I have given center point and radius for an arc function.
Thanks a million .
This should help, try this:
<canvas id="myCanvas" width="200" height="200"></canvas>
<script>
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 75;
var startAngle = 0 * Math.PI;
var endAngle = 1 * Math.PI;
var counterClockwise = false;
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.lineTo(x - radius, 200);
context.lineTo(x + radius, 200);
context.closePath();
context.stroke();
context.fillStyle = 'red';
context.fill();
</script>
I'm currently trying to make 1 happy face and 1 sad face with canvas but the problem is I can't get 2 faces to appear, only one.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>My Site's Title</title>
</head>
<body>
<canvas id="myDrawing" width="800" height="200" style="border:1px solid #EEE">
</canvas>
<script>
var canvas = document.getElementById("myDrawing");
var ctx = canvas.getContext("2d");
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 75;
var startAngle = 0;
var endAngle = 2 * Math.PI;
function drawFace() {
ctx.beginPath();
ctx.arc(x, y, radius, startAngle, endAngle);
ctx.stroke();
ctx.fillStyle = "yellow";
ctx.fill();
}
function drawSmile(){
var x = canvas.width / 2;
var y = 150
var radius = 40;
var startAngle = 1.1 * Math.PI;
var endAngle = 1.9 * Math.PI;
ctx.beginPath();
ctx.arc(x, y, radius, startAngle, endAngle);
ctx.lineWidth = 7;
// line color
ctx.strokeStyle = 'black';
ctx.stroke();
}
function drawEyes(){
var centerX = 40;
var centerY = 0;
var radius = 10;
// save state
ctx.save();
// translate context so height is 1/3'rd from top of enclosing circle
ctx.translate(canvas.width / 2, canvas.height / 3);
// scale context horizontally by 50%
ctx.scale(.5, 1);
// draw circle which will be stretched into an oval
ctx.beginPath();
ctx.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
// restore to original state
ctx.restore();
// apply styling
ctx.fillStyle = 'black';
ctx.fill();
ctx.lineWidth = 2;
ctx.strokeStyle = 'black';
ctx.stroke();
//left eye
var centerX = -40;
var centerY = 0;
var radius = 10;
// save state
ctx.save();
// translate context so height is 1/3'rd from top of enclosing circle
ctx.translate(canvas.width / 2, canvas.height / 3);
// scale context horizontally by 50%
ctx.scale(.5, 1);
// draw circle which will be stretched into an oval
ctx.beginPath();
ctx.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
// restore to original state
ctx.restore();
// apply styling
ctx.fillStyle = 'black';
ctx.fill();
ctx.lineWidth = 2;
ctx.strokeStyle = 'black';
ctx.stroke();
}
drawFace()
function drawHappyFace(){
drawFace();
drawEyes();
drawSmile();
}
drawHappyFace();
// SECOND FACE - HAPPY FACE
<canvas id="canvas" width="200" height="200" style="border:1px solid #EEE">
</canvas>
<script>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 75;
var startAngle = 0;
var endAngle = 2 * Math.PI;
function drawFace() {
ctx.beginPath();
ctx.arc(x, y, radius, startAngle, endAngle);
ctx.stroke();
ctx.fillStyle = "yellow";
ctx.fill();
}
function drawSmile(){
var x = canvas.width / 2;
var y = 150
var radius = 40;
var startAngle = 1.9 * Math.PI;
var endAngle = 1.1 * Math.PI;
ctx.beginPath();
ctx.arc(x, y, radius, startAngle, endAngle);
ctx.lineWidth = 7;
// line color
ctx.strokeStyle = 'black';
ctx.stroke();
}
function drawEyes(){
var centerX = 40;
var centerY = 0;
var radius = 10;
// save state
ctx.save();
// translate context so height is 1/3'rd from top of enclosing circle
ctx.translate(canvas.width / 2, canvas.height / 3);
// scale context horizontally by 50%
ctx.scale(.5, 1);
// draw circle which will be stretched into an oval
ctx.beginPath();
ctx.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
// restore to original state
ctx.restore();
// apply styling
ctx.fillStyle = 'black';
ctx.fill();
ctx.lineWidth = 2;
ctx.strokeStyle = 'black';
ctx.stroke();
//left eye
var centerX = -40;
var centerY = 0;
var radius = 10;
// save state
ctx.save();
// translate context so height is 1/3'rd from top of enclosing circle
ctx.translate(canvas.width / 2, canvas.height / 3);
// scale context horizontally by 50%
ctx.scale(.5, 1);
// draw circle which will be stretched into an oval
ctx.beginPath();
ctx.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
// restore to original state
ctx.restore();
// apply styling
ctx.fillStyle = 'black';
ctx.fill();
ctx.lineWidth = 2;
ctx.strokeStyle = 'black';
ctx.stroke();
}
drawFace()
function drawHappyFace(){
drawFace();
drawEyes();
drawSmile();
}
drawHappyFace();
</script>
</body>
</html>
</body>
</html>
I cna only get one of the faces to appear at once, for some reason, but I want both at the same time!
you can't have multiple functions with the same name because the second one overrides (hides) the first one; doesn't matter if they are in the same <script> tag or not (they can even be in different files)
change the name of the functions for the second face if you are such a beginner, but you should provide arguments to the function which will let you choose between multiple canvases and shapes using single function
it can look like this:
http://jsfiddle.net/Y5rUH/2/
I am just learning some details about html5 canvas, and in the progress, I am trying to build a simple color wheel by wedges (build a 1 degree wedge at a time and add it up to 360 degree). However, I am getting some weird marks on the gradient as shown in the following image:
.
Here is the fiddle that produced the colorwheel: http://jsfiddle.net/53JBM/
In particular, this is the JS code:
var canvas = document.getElementById("picker");
var context = canvas.getContext("2d");
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 100;
var counterClockwise = false;
for(var angle=0; angle<=360; angle+=1){
var startAngle = (angle-1)*Math.PI/180;
var endAngle = angle * Math.PI/180;
context.beginPath();
context.moveTo(x, y);
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.closePath();
context.fillStyle = 'hsl('+angle+', 100%, 50%)';
context.fill();
}
If anyone can point out what I am doing wrong or if there is a better way to accomplish what I am attempting to do it would be much appreciated :)
Is this enough to you, please check
var startAngle = (angle-2)*Math.PI/180;
Try this it looks great.
Thanks by the way this is exactly what I was trying to make.
var canvas = document.getElementById("picker");
var context = canvas.getContext("2d");
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 100;
var counterClockwise = false;
for(var angle=0; angle<=360; angle+=1){
var startAngle = (angle-2)*Math.PI/180;
var endAngle = angle * Math.PI/180;
context.beginPath();
context.moveTo(x, y);
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.closePath();
var gradient = context.createRadialGradient(x, y, 0, x, y, radius);
gradient.addColorStop(0,'hsl('+angle+', 10%, 100%)');
gradient.addColorStop(1,'hsl('+angle+', 100%, 50%)');
context.fillStyle = gradient;
context.fill();
}
<body>
<canvas id="picker"></canvas>
</body>
Similar approach, just for the color
var canvas = document.getElementById("picker");
var context = canvas.getContext("2d");
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 50;
var thickness = 0.6;
for(var angle=0; angle<=360; angle+=1){
var startAngle = (angle-2)*Math.PI/180;
var endAngle = angle * Math.PI/180;
context.beginPath();
context.arc(x, y, (1-thickness/2)*radius, startAngle, endAngle, false);
context.lineWidth = thickness*radius;
context.strokeStyle = 'hsl('+angle+', 100%, 50%)';
context.stroke();
}
<body>
<canvas id="picker"></canvas>
</body>
Edit: full project here: https://github.com/dersimn/jquery-colorwheel
You can draw arcs and you can draw images on a canvas using javascript, but is there anyway to do both? that is, is there anyway to draw an image as the arc instead of a solid line?
If not, is there a seperate way to arc an image?
I tried doing a pixel-by-pixel transformation of the image along the points of an arc, but it ended up being very slow and looking pretty poor since I can't directly get pixel data from javascript (or can you? I didnt see a way) so for each pixel, I needed to calculate the point along the arc, draw the current image pixel, refetch it, draw the image data to the calculated point, then clear that point on the canvas.
Have you tried setting the strokeStyle to a CanvasPattern based on an image? It looks like you could do something like this (assuming img is an HTMLImageElement that you want to draw from and ctx is a CanvasRenderingContext2D):
var pattern = ctx.createPattern(img, "repeat");
ctx.strokeStyle = pattern;
ctx.beginPath();
ctx.arc(123, 408, 80, 0, 1.5*Math.PI, false);
ctx.stroke();
Use this html to create arc : -
<canvas id="myCanvas" width="578" height="250"></canvas>
<script>
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 75;
var startAngle = .8 * Math.PI;
var endAngle = 2.2 * Math.PI;
var counterClockwise = false;
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.lineWidth = 30;
// line color
context.strokeStyle = 'blue';
context.stroke();
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 75;
var startAngle = 8 * Math.PI;
var endAngle =2.3 * Math.PI;
var counterClockwise = false;
context.beginPath();
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.lineWidth = 30;
// line color
context.strokeStyle = 'red';
context.stroke();
</script>