I am trying to achieve a tracing effect where the lines have a faded trail. The way I am trying to do it is simply by drawing the solid background once, and then on further frames draw a transparent background before drawing the new lines, so that you can still see a little of the image before it.
The issue is that I do want the lines to fade out completely after some time, but they seem to leave a permanent after image, even after drawing over them repeatedly.
I've tried setting different globalCompositeOperation(s) and it seemed like I was barking up the wrong tree there.
This code is called once
//initiate trace bg
traceBuffer.getContext("2d").fillStyle = "rgba(0, 30, 50, 1)";
traceBuffer.getContext("2d").fillRect(0, 0, traceBuffer.width, traceBuffer.height);
then inside the setInterval function it calls
//draw transparent background
ctx.fillStyle = "rgba(0, 30, 50, 0.04)";
ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
//set drawing settings
ctx.strokeStyle = "#AAAAAA";
ctx.lineWidth = 4;
for (let i = 0; i < tracer.layer2.length; i++){
ctx.beginPath();
ctx.moveTo(newX, newY);
ctx.lineTo(oldX, oldY);
ctx.stroke();
}
Here's an example: https://i.imgur.com/QTkeIVf.png
On the left is what I am currently getting, and on the right is the edit of what I actually want to happen.
This is how I would do it. I would build a history of the particles moving on the track. The older the position the smaller the value of the alpha value for the fill. Also for a nicer effect I would reduce the size of the circle.
I hope this is what you need.
PS: I would have loved to have your curve. Since I don't have it I've drawn a different one.
const hypotrochoid = document.getElementById("hypotrochoid");
const ctx = hypotrochoid.getContext("2d");
const cw = (hypotrochoid.width = 300);
const ch = (hypotrochoid.height = 300);
const cx = cw / 2,
cy = ch / 2;
ctx.lineWidth = 1;
ctx.strokeStyle = "#d9d9d9";
// variables for the hypotrochoid
let a = 90;
let b = 15;
let h = 50;
// an array where to save the points used to draw the track
let track = [];
//add points to the track array. This will be used to draw the track for the particles
for (var t = 0; t < 2 * Math.PI; t += 0.01) {
let o = {};
o.x = cx + (a - b) * Math.cos(t) + h * Math.cos((a - b) / b * t);
o.y = cy + (a - b) * Math.sin(t) - h * Math.sin((a - b) / b * t);
track.push(o);
}
// a function to draw the track
function drawTrack(ry) {
ctx.beginPath();
ctx.moveTo(ry[0].x, ry[0].y);
for (let t = 1; t < ry.length; t++) {
ctx.lineTo(ry[t].x, ry[t].y);
}
ctx.closePath();
ctx.stroke();
}
// a class of points that are moving on the track
class Point {
constructor(pos) {
this.pos = pos;
this.r = 3;//the radius of the circle
this.history = [];
this.historyLength = 40;
}
update(newPos) {
let old_pos = {};
old_pos.x = this.pos.x;
old_pos.y = this.pos.y;
//save the old position in the history array
this.history.push(old_pos);
//if the length of the track is longer than the max length allowed remove the extra elements
if (this.history.length > this.historyLength) {
this.history.shift();
}
//gry the new position on the track
this.pos = newPos;
}
draw() {
for (let i = 0; i < this.history.length; i++) {
//calculate the alpha value for every element on the history array
let alp = i * 1 / this.history.length;
// set the fill style
ctx.fillStyle = `rgba(0,0,0,${alp})`;
//draw an arc
ctx.beginPath();
ctx.arc(
this.history[i].x,
this.history[i].y,
this.r * alp,
0,
2 * Math.PI
);
ctx.fill();
}
}
}
// 2 points on the track
let p = new Point(track[0]);
let p1 = new Point(track[~~(track.length / 2)]);
let frames = 0;
let n, n1;
function Draw() {
requestAnimationFrame(Draw);
ctx.clearRect(0, 0, cw, ch);
//indexes for the track position
n = frames % track.length;
n1 = (~~(track.length / 2) + frames) % track.length;
//draw the track
drawTrack(track);
// update and draw the first point
p.update(track[n]);
p.draw();
// update and draw the second point
p1.update(track[n1]);
p1.draw();
//increase the frames counter
frames++;
}
Draw();
canvas{border:1px solid}
<canvas id="hypotrochoid"></canvas>
Please check out this code :
(function() {
var cnv = document.getElementById('canvas');
if (cnv.getContext) {
var ctx = cnv.getContext('2d');
} else {
alert('God Damn it ...');
}
function initialize() {
window.addEventListener('resize', resizeCanvas, false);
resizeCanvas();
}
function draw() {
for (var i = 0; i < 25; i++) {
width = Math.random() * cnv.width;
height = Math.random() * cnv.height;
ctx.beginPath();
ctx.arc(width, height, 15, 0, Math.PI * 2);
ctx.strokeStyle = '#E1E1E1';
ctx.lineWidth = 1;
ctx.stroke();
}
}
function resizeCanvas() {
cnv.width = window.innerWidth;
cnv.height = window.innerHeight;
draw();
}
initialize();
})();
I have created 25 Circle shape with random position and I want to create an animation that scales up or down in a interval time. I know about setInterval but how should I call my shape to do something on it?
The first thing you will want to do is to have a place to store the position of your circles, since they are all going to be the same radius we can just store the x and y position. For that we can create a Circle function ("class") and have an array of circles:
var circles = []; // Array to store our circles
var minRadius = 1; // The smallest radius we can hit
var maxRadius = 100; // The largest radius we can hit
var currentRadius = 15;// The current radius of all our circles
var scaleBy = 1; // How the radius changes
var cnv = document.getElementById('canvas');
// ...
function initialize() {
window.addEventListener('resize', resizeCanvas, false);
resizeCanvas();
// Populating the array of circles to use when drawing
for (var i = 0; i < 25; i++) { // Make sure to do this after re-sizing the canvas
width = Math.random() * cnv.width;
height = Math.random() * cnv.height;
circles.push(new Circle(width, height));
}
}
// ...
function Circle(x, y){
this.x = x;
this.y = y;
}
Circle.prototype.draw = function(){
ctx.beginPath();
ctx.arc(this.x, this.y, currentRadius, 0, Math.PI * 2);
ctx.strokeStyle = '#E1E1E1';
ctx.lineWidth = 5;
ctx.stroke();
}
Now that you have some circles when you call draw you can iterate through the array and call circle.draw() for each circle element in your array:
function draw() {
// Clear the screen and draw the circles in our array
ctx.clearRect(0,0, cnv.width, cnv.height);
for (var i = 0; i < circles.length; i++) {
circles[i].draw();
}
}
One note is you will want to use ctx.clearRect(0,0, cnv.width, cnv.height) to clear the screen before drawing.
Finally you can now use setInterval to change the currentRadius (*While there is nothing wrong with setInterval I'd recommend using window.requestAnimationFrame for animation as it's a bit more smooth and efficient method). Then when you call draw it will draw the circles with the new value of currentRadius. In this example I'm going to have it start at 15. Then increase by 1 until it hits maxRadius, then we can flip the sign of scaleBy to start decreasing the radius to make them smaller. Finally when it his our minRadius you can flip the sign of scaleBy again to make it start scaling up again:
var timer = setInterval( function(){
// If we hit our min or max start scaling in the other direction
if(currentRadius > maxRadius || currentRadius < minRadius){
scaleBy *= -1;
}
currentRadius += scaleBy;
draw();
}, 50);
Below is a code snippet of the complete program:
(function() {
var circles = [];
var minRadius = 1;
var maxRadius = 100;
var currentRadius = 15;
var scaleBy = 1;
var cnv = document.getElementById('canvas');
if (cnv.getContext) {
var ctx = cnv.getContext('2d');
} else {
alert('God Damn it ...');
}
function initialize() {
window.addEventListener('resize', resizeCanvas, false);
resizeCanvas();
for (var i = 0; i < 25; i++) {
width = Math.random() * cnv.width;
height = Math.random() * cnv.height;
circles.push(new Circle(width, height));
}
}
function draw() {
ctx.clearRect(0,0, cnv.width, cnv.height);
for (var i = 0; i < circles.length; i++) {
circles[i].draw();
}
}
function resizeCanvas() {
cnv.width = window.innerWidth;
cnv.height = window.innerHeight;
}
function Circle(x, y){
this.x = x;
this.y = y;
}
Circle.prototype.draw = function(){
ctx.beginPath();
ctx.arc(this.x, this.y, currentRadius, 0, Math.PI * 2);
ctx.strokeStyle = '#E1E1E1';
ctx.lineWidth = 5;
ctx.stroke();
}
initialize();
var timer = setInterval( function(){
if(currentRadius > maxRadius || currentRadius < minRadius){
scaleBy *= -1;
}
currentRadius += scaleBy;
draw();
}, 50);
})();
<canvas id="canvas"></canvas>
I am visualising flight paths with D3 and Canvas. In short, I have data for each flight's origin and destination
as well as the airport coordinates. The ideal end state is to have an indiviudal circle representing a plane moving
along each flight path from origin to destination. The current state is that each circle gets visualised along the path,
yet the removal of the previous circle along the line does not work as clearRect gets called nearly constantly.
Current state:
Ideal state (achieved with SVG):
The Concept
Conceptually, an SVG path for each flight is produced in memory using D3's custom interpolation with path.getTotalLength() and path.getPointAtLength() to move the circle along the path.
The interpolator returns the points along the path at any given time of the transition. A simple drawing function takes these points and draws the circle.
Key functions
The visualisation gets kicked off with:
od_pairs.forEach(function(el, i) {
fly(el[0], el[1]); // for example: fly('LHR', 'JFK')
});
The fly() function creates the SVG path in memory and a D3 selection of a circle (the 'plane') - also in memory.
function fly(origin, destination) {
var pathElement = document.createElementNS(d3.namespaces.svg, 'path');
var routeInMemory = d3.select(pathElement)
.datum({
type: 'LineString',
coordinates: [airportMap[origin], airportMap[destination]]
})
.attr('d', path);
var plane = custom.append('plane');
transition(plane, routeInMemory.node());
}
The plane gets transitioned along the path by the custom interpolater in the delta() function:
function transition(plane, route) {
var l = route.getTotalLength();
plane.transition()
.duration(l * 50)
.attrTween('pointCoordinates', delta(plane, route))
// .on('end', function() { transition(plane, route); });
}
function delta(plane, path) {
var l = path.getTotalLength();
return function(i) {
return function(t) {
var p = path.getPointAtLength(t * l);
draw([p.x, p.y]);
};
};
}
... which calls the simple draw() function
function draw(coords) {
// contextPlane.clearRect(0, 0, width, height); << how to tame this?
contextPlane.beginPath();
contextPlane.arc(coords[0], coords[1], 1, 0, 2*Math.PI);
contextPlane.fillStyle = 'tomato';
contextPlane.fill();
}
This results in an extending 'path' of circles as the circles get drawn yet not removed as shown in the first gif above.
Full code here: http://blockbuilder.org/larsvers/8e25c39921ca746df0c8995cce20d1a6
My question is, how can I achieve to draw only a single, current circle while the previous circle gets removed without interrupting other circles being drawn on the same canvas?
Some failed attempts:
The natural answer is of course context.clearRect(), however, as there's a time delay (roughly a milisecond+) for each circle to be drawn as it needs to get through the function pipeline clearRect gets fired almost constantly.
I tried to tame the perpetual clearing of the canvas by calling clearRect only at certain intervals (Date.now() % 10 === 0 or the like) but that leads to no good either.
Another thought was to calculate the previous circle's position and remove the area specifically with a small and specific clearRect definition within each draw() function.
Any pointers very much appreciated.
Handling small dirty regions, especially if there is overlap between objects quickly becomes very computationally heavy.
As a general rule, a average Laptop/desktop can easily handle 800 animated objects if the computation to calculate position is simple.
This means that the simple way to animate is to clear the canvas and redraw every frame. Saves a lot of complex code that offers no advantage over the simple clear and redraw.
const doFor = (count,callback) => {var i=0;while(i < count){callback(i++)}};
function createIcon(drawFunc){
const icon = document.createElement("canvas");
icon.width = icon.height = 10;
drawFunc(icon.getContext("2d"));
return icon;
}
function drawPlane(ctx){
const cx = ctx.canvas.width / 2;
const cy = ctx.canvas.height / 2;
ctx.beginPath();
ctx.strokeStyle = ctx.fillStyle = "red";
ctx.lineWidth = cx / 2;
ctx.lineJoin = "round";
ctx.lineCap = "round";
ctx.moveTo(cx/2,cy)
ctx.lineTo(cx * 1.5,cy);
ctx.moveTo(cx,cy/2)
ctx.lineTo(cx,cy*1.5)
ctx.stroke();
ctx.lineWidth = cx / 4;
ctx.moveTo(cx * 1.7,cy * 0.6)
ctx.lineTo(cx * 1.7,cy*1.4)
ctx.stroke();
}
const planes = {
items : [],
icon : createIcon(drawPlane),
clear(){
planes.items.length = 0;
},
add(x,y){
planes.items.push({
x,y,
ax : 0, // the direction of the x axis of this plane
ay : 0,
dir : Math.random() * Math.PI * 2,
speed : Math.random() * 0.2 + 0.1,
dirV : (Math.random() - 0.5) * 0.01, // change in direction
})
},
update(){
var i,p;
for(i = 0; i < planes.items.length; i ++){
p = planes.items[i];
p.dir += p.dirV;
p.ax = Math.cos(p.dir);
p.ay = Math.sin(p.dir);
p.x += p.ax * p.speed;
p.y += p.ay * p.speed;
}
},
draw(){
var i,p;
const w = canvas.width;
const h = canvas.height;
for(i = 0; i < planes.items.length; i ++){
p = planes.items[i];
var x = ((p.x % w) + w) % w;
var y = ((p.y % h) + h) % h;
ctx.setTransform(-p.ax,-p.ay,p.ay,-p.ax,x,y);
ctx.drawImage(planes.icon,-planes.icon.width / 2,-planes.icon.height / 2);
}
}
}
const ctx = canvas.getContext("2d");
function mainLoop(){
if(canvas.width !== innerWidth || canvas.height !== innerHeight){
canvas.width = innerWidth;
canvas.height = innerHeight;
planes.clear();
doFor(800,()=>{ planes.add(Math.random() * canvas.width, Math.random() * canvas.height) })
}
ctx.setTransform(1,0,0,1,0,0);
// clear or render a background map
ctx.clearRect(0,0,canvas.width,canvas.height);
planes.update();
planes.draw();
requestAnimationFrame(mainLoop)
}
requestAnimationFrame(mainLoop)
canvas {
position : absolute;
top : 0px;
left : 0px;
}
<canvas id=canvas></canvas>
800 animated points
As pointed out in the comments some machines may be able to draw a circle if one colour and all as one path slightly quicker (not all machines). The point of rendering an image is that it is invariant to the image complexity. Image rendering is dependent on the image size but colour and alpha setting per pixel have no effect on rendering speed. Thus I have changed the circle to show the direction of each point via a little plane icon.
Path follow example
I have added a way point object to each plane that in the demo has a random set of way points added. I called it path (could have used a better name) and a unique path is created for each plane.
The demo is to just show how you can incorporate the D3.js interpolation into the plane update function. The plane.update now calls the path.getPos(time) which returns true if the plane has arrived. If so the plane is remove. Else the new plane coordinates are used (stored in the path object for that plane) to set the position and direction.
Warning the code for path does little to no vetting and thus can easily be made to throw an error. It is assumed that you write the path interface to the D3.js functionality you want.
const doFor = (count,callback) => {var i=0;while(i < count){callback(i++)}};
function createIcon(drawFunc){
const icon = document.createElement("canvas");
icon.width = icon.height = 10;
drawFunc(icon.getContext("2d"));
return icon;
}
function drawPlane(ctx){
const cx = ctx.canvas.width / 2;
const cy = ctx.canvas.height / 2;
ctx.beginPath();
ctx.strokeStyle = ctx.fillStyle = "red";
ctx.lineWidth = cx / 2;
ctx.lineJoin = "round";
ctx.lineCap = "round";
ctx.moveTo(cx/2,cy)
ctx.lineTo(cx * 1.5,cy);
ctx.moveTo(cx,cy/2)
ctx.lineTo(cx,cy*1.5)
ctx.stroke();
ctx.lineWidth = cx / 4;
ctx.moveTo(cx * 1.7,cy * 0.6)
ctx.lineTo(cx * 1.7,cy*1.4)
ctx.stroke();
}
const path = {
wayPoints : null, // holds way points
nextTarget : null, // holds next target waypoint
current : null, // hold previously passed way point
x : 0, // current pos x
y : 0, // current pos y
addWayPoint(x,y,time){
this.wayPoints.push({x,y,time});
},
start(){
if(this.wayPoints.length > 1){
this.current = this.wayPoints.shift();
this.nextTarget = this.wayPoints.shift();
}
},
getNextTarget(){
this.current = this.nextTarget;
if(this.wayPoints.length === 0){ // no more way points
return;
}
this.nextTarget = this.wayPoints.shift(); // get the next target
},
getPos(time){
while(this.nextTarget.time < time && this.wayPoints.length > 0){
this.getNextTarget(); // get targets untill the next target is ahead in time
}
if(this.nextTarget.time < time){
return true; // has arrivecd at target
}
// get time normalised ove time between current and next
var timeN = (time - this.current.time) / (this.nextTarget.time - this.current.time);
this.x = timeN * (this.nextTarget.x - this.current.x) + this.current.x;
this.y = timeN * (this.nextTarget.y - this.current.y) + this.current.y;
return false; // has not arrived
}
}
const planes = {
items : [],
icon : createIcon(drawPlane),
clear(){
planes.items.length = 0;
},
add(x,y){
var p;
planes.items.push(p = {
x,y,
ax : 0, // the direction of the x axis of this plane
ay : 0,
path : Object.assign({},path,{wayPoints : []}),
})
return p; // return the plane
},
update(time){
var i,p;
for(i = 0; i < planes.items.length; i ++){
p = planes.items[i];
if(p.path.getPos(time)){ // target reached
planes.items.splice(i--,1); // remove
}else{
p.dir = Math.atan2(p.y - p.path.y, p.x - p.path.x) + Math.PI; // add 180 because i drew plane wrong way around.
p.ax = Math.cos(p.dir);
p.ay = Math.sin(p.dir);
p.x = p.path.x;
p.y = p.path.y;
}
}
},
draw(){
var i,p;
const w = canvas.width;
const h = canvas.height;
for(i = 0; i < planes.items.length; i ++){
p = planes.items[i];
var x = ((p.x % w) + w) % w;
var y = ((p.y % h) + h) % h;
ctx.setTransform(-p.ax,-p.ay,p.ay,-p.ax,x,y);
ctx.drawImage(planes.icon,-planes.icon.width / 2,-planes.icon.height / 2);
}
}
}
const ctx = canvas.getContext("2d");
function mainLoop(time){
if(canvas.width !== innerWidth || canvas.height !== innerHeight){
canvas.width = innerWidth;
canvas.height = innerHeight;
planes.clear();
doFor(810,()=>{
var p = planes.add(Math.random() * canvas.width, Math.random() * canvas.height);
// now add random number of way points
var timeP = time;
// info to create a random path
var dir = Math.random() * Math.PI * 2;
var x = p.x;
var y = p.y;
doFor(Math.floor(Math.random() * 80 + 12),()=>{
var dist = Math.random() * 5 + 4;
x += Math.cos(dir) * dist;
y += Math.sin(dir) * dist;
dir += (Math.random()-0.5)*0.3;
timeP += Math.random() * 1000 + 500;
p.path.addWayPoint(x,y,timeP);
});
// last waypoin at center of canvas.
p.path.addWayPoint(canvas.width / 2,canvas.height / 2,timeP + 5000);
p.path.start();
})
}
ctx.setTransform(1,0,0,1,0,0);
// clear or render a background map
ctx.clearRect(0,0,canvas.width,canvas.height);
planes.update(time);
planes.draw();
requestAnimationFrame(mainLoop)
}
requestAnimationFrame(mainLoop)
canvas {
position : absolute;
top : 0px;
left : 0px;
}
<canvas id=canvas></canvas>
800 animated points
#Blindman67 is correct, clear and redraw everything, every frame.
I'm here just to say that when dealing with such primitive shapes as arc without too many color variations, it's actually better to use the arc method than drawImage().
The idea is to wrap all your shapes in a single path declaration, using
ctx.beginPath(); // start path declaration
for(i; i<shapes.length; i++){ // loop through our points
ctx.moveTo(pt.x + pt.radius, pt.y); // default is lineTo and we don't want it
// Note the '+ radius', arc starts at 3 o'clock
ctx.arc(pt.x, pt.y, pt.radius, 0, Math.PI*2);
}
ctx.fill(); // a single fill()
This is faster than drawImage, but the main caveat is that it works only for single-colored set of shapes.
I've made an complex plotting app, where I do draw a lot (20K+) of entities, with animated positions. So what I do, is to store two sets of points, one un-sorted (actually sorted by radius), and one
sorted by color. I then do use the sorted-by-color one in my animations loop, and when the animation is complete, I draw only the final frame with the sorted-by-radius (after I filtered the non visible entities). I achieve 60fps on most devices. When I tried with drawImage, I was stuck at about 10fps for 5K points.
Here is a modified version of Blindman67's good answer's snippet, using this single-path approach.
/* All credits to SO user Blindman67 */
const doFor = (count,callback) => {var i=0;while(i < count){callback(i++)}};
const planes = {
items : [],
clear(){
planes.items.length = 0;
},
add(x,y){
planes.items.push({
x,y,
rad: 2,
dir : Math.random() * Math.PI * 2,
speed : Math.random() * 0.2 + 0.1,
dirV : (Math.random() - 0.5) * 0.01, // change in direction
})
},
update(){
var i,p;
for(i = 0; i < planes.items.length; i ++){
p = planes.items[i];
p.dir += p.dirV;
p.x += Math.cos(p.dir) * p.speed;
p.y += Math.sin(p.dir) * p.speed;
}
},
draw(){
var i,p;
const w = canvas.width;
const h = canvas.height;
ctx.beginPath();
ctx.fillStyle = 'red';
for(i = 0; i < planes.items.length; i ++){
p = planes.items[i];
var x = ((p.x % w) + w) % w;
var y = ((p.y % h) + h) % h;
ctx.moveTo(x + p.rad, y)
ctx.arc(x, y, p.rad, 0, Math.PI*2);
}
ctx.fill();
}
}
const ctx = canvas.getContext("2d");
function mainLoop(){
if(canvas.width !== innerWidth || canvas.height !== innerHeight){
canvas.width = innerWidth;
canvas.height = innerHeight;
planes.clear();
doFor(8000,()=>{ planes.add(Math.random() * canvas.width, Math.random() * canvas.height) })
}
ctx.setTransform(1,0,0,1,0,0);
// clear or render a background map
ctx.clearRect(0,0,canvas.width,canvas.height);
planes.update();
planes.draw();
requestAnimationFrame(mainLoop)
}
requestAnimationFrame(mainLoop)
canvas {
position : absolute;
top : 0px;
left : 0px;
z-index: -1;
}
<canvas id=canvas></canvas>
8000 animated points
Not directly related but in case you've got part of your drawings that don't update at the same rate as the rest (e.g if you want to highlight an area of your map...) then you might also consider separating your drawings in different layers, on offscreen canvases. This way you'd have one canvas for the planes, that you'd clear every frame, and other canvas for other layers that you would update at different rate. But that's an other story.
I need to draw a number line, that can allows to ask an input and draw the point in the line, or move some point over the line.
like this example:
https://www.khanacademy.org/math/arithmetic/multiplication-division/multiplication_fun/e/number_line
i tried to use canvas but i can't get it, because i never used it before.
<canvas id="canvas"></canvas>
here the JS:
$(function() {
var canvas = $('canvas')[0];
var ctx = canvas.getContext('2d');
var w = canvas.width = 700;
var h = canvas.height = 400;
var x0 = w/2;
var starti=-10;
var endi=10;
var interval = 20; //10 -> 20 ... 15 -> x
var step = 2;
var steps = 5;
with(ctx) {
fillStyle = '#FFFFFF';
fillRect(0, 0, w, h);
fill();
beginPath();
lineWidth = 2;
strokeStyle = '#000';
moveTo(w/7, h/2);
lineTo(6*w/7, h/2);
stroke();
moveTo(w/7, h/2);
lineTo(w/7+10, h/2+10); //left arrow bottom line
stroke();
moveTo(w/7, h/2);
lineTo(w/7+10, h/2-10); //left arrow top line
stroke();
moveTo(6*w/7, h/2);
lineTo(6*w/7-10, h/2+10); //right arrow bot line
stroke();
moveTo(6*w/7, h/2);
lineTo(6*w/7-10, h/2-10); //right arrow top line
stroke();
for(var i = starti;i <= endi; i++) {
beginPath();
strokeStyle = '#8C8C8C';
lineWidth = 2;
moveTo(w/2 + i * interval, h/2 - 10);
lineTo(w/2 + i * interval, h/2 + 10);
fillStyle = '#000';
fillText(i/10, (w/2 + i * interval )- 5, h/2 + 25);
if(!i) {
strokeStyle = '#F25050';
}
fill();
stroke();
}
}
drawOperation(x0,step, steps);
});
doesn't matter if you know another solution instead of canvas.
Somehow I cannot get it the canvas clear in my canvas tag, it only clear some portion and i have put canvas.witdh and height as the argument. Originally it should clear all of it when a button is clicked and clearGraph() function is triggered and redraw. Please do help me.
You can view it from here. http://jsfiddle.net/qH2Lr/1/
function init() {
// data sets -- set literally or obtain from an ajax call
var dataName = [ "You", "Competitors" ];
var dataValue = [ 2600, 4000];
// set these values for your data
numSamples = 2;
maxVal = 5000;
var stepSize = 1000;
var colHead = 50;
var rowHead = 60;
var margin = 10;
var header = "Millions"
var can = document.getElementById("can");
ctx = can.getContext("2d");
ctx.fillStyle = "black"
yScalar = (can.height - colHead - margin) / (maxVal);
xScalar = (can.width - rowHead) / (numSamples + 1);
ctx.strokeStyle = "rgba(128,128,255, 0.5)"; // light blue line
ctx.beginPath();
// print column header
ctx.font = "14pt Helvetica"
ctx.fillText(header, 0, colHead - margin);
// print row header and draw horizontal grid lines
ctx.font = "12pt Helvetica"
var count = 0;
for (scale = maxVal; scale >= 0; scale -= stepSize) {
y = colHead + (yScalar * count * stepSize);
ctx.fillText(scale, margin,y + margin);
ctx.moveTo(rowHead, y)
ctx.lineTo(can.width, y)
count++;
}
ctx.stroke();
// label samples ctx.shadowColor = 'rgba(128,128,128, 0.5)';
ctx.shadowOffsetX = 20;
ctx.shadowOffsetY = 1;
// translate to bottom of graph and scale x,y to match data
ctx.translate(0, can.height - margin);
ctx.font = "14pt Helvetica";
ctx.textBaseline = "bottom";
for (i = 0; i < 4; i++) {
calcY(dataValue[i]);
ctx.fillText(dataName[i], xScalar * (i + 1), y - margin);
}
// set a color and a shadow
ctx.fillStyle = "green";
ctx.scale(xScalar, -1 * yScalar);
// draw bars
for (i = 0; i < 4; i++) {
ctx.fillRect(i + 1, 0, 0.5, dataValue[i]);
}
}
function calcY(value) {
y = can.height - value * yScalar;
}
function clearGraph() {
var canvas = document.getElementById("can");
var ctx = canvas.getContext("2d");
// Will always clear the right space
ctx.clearRect(0, 0, canvas.width, canvas.height);
}
</script>
You are making many changes to the context such as scale and translate.
These will affect clearRect() as well. I would suggest in this case to use the save() and restore() methods. save() stores the current state of the context incl. transforms:
ctx = can.getContext("2d");
ctx.save(); // after obtaining the context
... rest of code ...
ctx.restore(); // before clearing
ctx.clearRect(0, 0, can.width, can.height);
Now you can see it works as intended:
Modified fiddle
Of course, clearing right after drawing everything is probably not the real intention but to show that it do work (when you eventually need it - put it first in the code if you intend to redraw the graph).