For an assignment I need to animate something simple using CSS and JavaScript. I've been able to figure out the CSS but everything I read to make an object fade in using JavaScript just doesn't seem to work with the object I drew in JavaScript. I just wanted to draw a circle in JavaScript and then animate it to fade in in 5 seconds.
Here is the basic Code I have so far:
HTML:
<body onload="draw();">
<canvas id="circle" width="450" height="450"></canvas>
</body>
JavaScript:
<script>
function draw()
{
var canvas = document.getElementById('circle');
if (canvas.getContext)
{
var ctx = canvas.getContext('2d');
var X = canvas.width / 2;
var Y = canvas.height / 2;
var R = 45;
ctx.beginPath();
ctx.arc(X, Y, R, 0, 2 * Math.PI, false);
ctx.lineWidth = 3;
ctx.strokeStyle = '#645862';
ctx.stroke();
}
}
</script>
As you can see I only have the circle part of the code. I have tried multiple versions of different fade in animations but I just can't quite get them to work. I'm not very good at JavaScript. It's the one language I have trouble understanding for some reason. I'm also really sick right now otherwise I would be troubleshooting more reasons as to why it isn't working.
To understand how a canvas works, you need to know that it's just a place to display something, and initially it doesn't do anything on its own. You've drawn the circle once, which is enough to display the circle, but not to animate it in any way.
If we want to move the circle in any direction, we must clear the canvas of the already drawn circle and draw the circle in a different place, changing its coordinates by N pixels. The same goes for transparency. We must change the transparency of the color of the circle in each frame, and draw the circle again and again.
This is how 2D and 3D canvas works, as well as all video games - they draw scenes 60 times per second, changing some values along the way, such as coordinates, values, color, transparency, height and width.
In order for this to work, we need two additional variables, opacity and the direction (fading) in which the opacity changes, to know whether the circle appears or disappears.
Also important is the recursive call to our draw() function. We will call it constantly, and we will constantly redraw our image on the canvas.
I also want to point out some conceptual mistakes in your code.
Dont use "var", it is deprecated. Use "let","const". Also don`t repeat "var","var","var" in every line. Use commas.
Dont use onload,onclick and others HTML on-attributes. They are only suitable for educational purposes, not for real work. Use script tag and document event listeners.
Dont name canvas id like "circle","box" etc. It is not a circle and a box, it is a canvas.
Use document.querySelector instead of document.getElementById. It is more modern
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Canvas opacity animation</title>
</head>
<body>
<canvas id="canvas" width="450" height="450"></canvas>
<script>
document.addEventListener("DOMContentLoaded",()=>{
const OPACITY_SPEED = .005
let canvas = document.querySelector('canvas'),
context = canvas.getContext('2d'),
opacity = 1,
fading = true
draw()
function draw(){
// clear canvas for redrawing (important!)
context.clearRect(0, 0, canvas.width, canvas.height);
let circleX = canvas.width/2,
circleY = canvas.height/2,
radius = 45
// changing circle opacity
if(fading) opacity -= OPACITY_SPEED
else opacity += OPACITY_SPEED
// check if we need to fade in or to fade out
if(opacity >= 1) fading = true
if(opacity <= 0) fading = false
// draw circle
context.beginPath();
context.arc(circleX, circleY, radius, 0, 2 * Math.PI, false);
context.lineWidth = 3;
context.strokeStyle = `rgba(0, 0, 0, ${opacity})`;
context.stroke();
// call draw() again and again
requestAnimationFrame(draw)
}
})
</script>
</body>
</html>
Related
today i've got a problem regarding JavaScript.
I was given an exercise which consists on create a circle on the screen, using JavaScript, and then make it move to the right.
So the problem comes when i put in the function animate().
The code by itself works, it creates a circle, but when i insert the function animate() , put the code in it, and then try to recall it with requestFrameAnimation(animate), it just doesn't draw on the screen.
Code right down here. I've tried everything i am capable of, but couldn't fix it.
Thanks for the replies.
HTML:
<head>
<style type="text/css">
canvas{
border:1px solid black;
}
body{
margin:0px;
background-color:red;
</style>
</head>
<body>
<canvas></canvas>
<script src="canvas.js"></script>
</script>
</body>
JS:
canvas = document.querySelector('canvas'); //CANVAS SELECTOR
canvas.width = window.innerWidth; //MATCHING THE CANVAS WIDTH WITH THE WINDOW WIDTH
canvas.height = window.innerHeight; //********************HEIGHT***************HEIGHT
context=canvas.getContext("2d");
var x=200;
function animate(){ //Starting the function
context.beginPath(); //Initializing a Path of drawings
context.arc(x,200,100,0,Math.PI*2, true); //drawing the circle
context.fillStyle="rgba(120,10,200,0.5)"; //filling the circle
context.fill();
context.strokeStyle = 'blue'; //giving the circle a strokeline
context.stroke();
x+=1; //increasing the circle x so that it keeps moving towards right
requestAnimationFrame(animate); //calling back to the function so it keeps drawing infinitely.
}
I'm trying to build a very simple animation function. I'm using this tutorial to build my project:
https://www.youtube.com/watch?v=hUCT4b4wa-8
The result after the button is clicked should be a green box moving across the page from left to right. When the button is clicked, nothing happens and I don't get any console errors.
Here's my fiddle:
https://jsfiddle.net/xkhpmrtu/7/
And here's a snippet of my code:
<!DOCTYPE html>
<head>
<meta charset="utf-8" />
<style type="text/css">
canvas {
border: 1px solid #666;
}
</style>
<script type="application/javascript" language="javascript">
function anim(x,y) {
var canvas = document.getElementById('canvas');//reference to canvas element on page
var ctx = canvas.getContext('2d');//establish a 2d context for the canvas element
ctx.save();//save canvas state if required (not required for the tutoriral anaimation, but doesn't hurt the script so it stays for now)
ctx.clearRect(0, 0, 550, 400);//clears the canvas for redrawing the scene.
ctx.fillStyle = "rgba(0,200,0,1)";//coloring the rectangle
ctx.fillRect = (x, 20, 50, 50);//drawing the rectangle
ctx.restore();//this restores the canvas to it's original state when we saved it on (at the time) line 18
x += 5; //increment the x position by some numeric value
var loopTimer = setTimeout('draw('+x+','+y+')', 2000);// setTimeout is a function that
</script>
</head>
<body>
<button onclick="animate(0,0)">Draw</button>
<canvas id="canvas" width="550" height="400"></canvas>
</body>
Any idea what I'm doing wrong?
I just had a look at the tutorial link. I will give if a major thumbs down as it demonstrates how not to animate and how not to do many other things in Javascript.
First the script tag and what is wrong with it
// type and language default to the correct setting for javascrip
// <script type="application/javascript" language="javascript">
<script>
function anim(x,y) {
// get the canvas once. Getting the canvas for each frame of an
// animation will slow everything down. Same for ctx though will not
// create as much of a slowdown it is not needed for each frame
// var canvas = document.getElementById('canvas');
// var ctx = canvas.getContext('2d');
// Dont use save unless you have to. It is not ok to add it if not needed
// ctx.save();
// dont use literal values, canvas may change size
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.fillStyle = "rgba(0,200,0,1)";
// this line is wrong should be ctx.fillRect(x, 20, 50, 50). It is correct in the video
ctx.fillRect = (x, 20, 50, 50);//drawing the rectangle
// restore not needed
//ctx.restore();
x += 5; //increment the x position by some numeric value
// creating a string for a timer is bad. It invokes the parser and is slooowwwwww...
// For animations you should avoid setTimeout altogether and use
// requestAnimationFrame
// var loopTimer = setTimeout('draw('+x+','+y+')', 2000);
requestAnimationFrame(draw);
// you were missing the closing curly.
}
</script>
There is lots more wrong with the tut. It can be excused due to it being near 5 years old. You should look for more up todate tutorials as 5 years is forever in computer technology.
Here is how to do it correctly.
// This script should be at the bottom of the page just befor the closing body tag
// If not you need to use the onload event to start the script.
// define a function that starts the animation
function startAnimation() {
animating = true; // flag we are now animating
x = 10;
y = 10;
// animation will start at next frame or restart at next frame if already running
}
// define the animation function
function anim() {
if (animating) { // only draw if animating
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.fillStyle = "red"; //coloring the rectangle
ctx.fillRect(x, y, 50, 50); //drawing the rectangle
x += xSpeed;
}
// set animation timer for next frame
requestAnimationFrame(anim);
}
// add a click listener to the start button. It calls the supplied function every time you click the button
startAnimButton.addEventListener("click", startAnimation);
const ctx = canvas.getContext('2d'); // get the 2d rendering context
// set up global variables to do the animation
var x, y, animating;
animating = false; // flag we are not animating
const xSpeed = 50 / 60; // Speed is 50 pixels per second at 60fps
// dont slow the animation down via frame rate
// slow it down by reducing speed.
// You only slow frame rate if the machine
// can not handle the load.
// start the animation loop
requestAnimationFrame(anim);
canvas {
border: 1px solid #666;
}
<!-- don't add events inline -->
<button id="startAnimButton">Draw</button>
<canvas id="canvas" width="512" height="128"></canvas>
I am seeking for a way that allows players to draw their own characters and later to be able to play with them in-game. To make the concept very simple lets make the drawn player just a 2d shape or a group of lines and circles or even a mix of both. I think this can be decomposed in these steps:
An empty canvas is made for the user to create what he wants:
By painting or something of that genre
By using a specific polygon creation interface that allows dragging and molding shapes;
Note: I was able to create a way to paint on canvas *** but I didn't find a way to let user drag and create shapes or something of that kind. I would more likely opt for the second option so some suggestions on how do this would be really appreciated.
window.onload = init;
function init() {
var canvas = document.getElementById('myCanvas');
var ctx = canvas.getContext('2d');
var painting = document.getElementById('paint');
var paint_style = getComputedStyle(painting);
canvas.width = "1024"
canvas.height = "1024";
var mouse = {
x: 0,
y: 0
};
canvas.addEventListener('mousemove', function(e) {
mouse.x = e.pageX - this.offsetLeft;
mouse.y = e.pageY - this.offsetTop;
}, false);
ctx.lineWidth = 3;
ctx.lineJoin = 'round';
ctx.lineCap = 'round';
ctx.strokeStyle = '#00CC99';
canvas.addEventListener('mousedown', function(e) {
ctx.beginPath();
ctx.moveTo(mouse.x, mouse.y);
canvas.addEventListener('mousemove', onPaint, false);
}, false);
canvas.addEventListener('mouseup', function() {
canvas.removeEventListener('mousemove', onPaint, false);
}, false);
var onPaint = function() {
ctx.lineTo(mouse.x, mouse.y);
ctx.stroke();
};
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Tojo - canvas draw</title>
<link rel="stylesheet" href="index.css">
</head>
<body>
<script src="app.js"></script>
<div id="paint"></div>
<canvas id="myCanvas" style="border: 3px solid black;"></canvas>
</body>
</html>
(paint on canvas snippet) ***
Somehow, I need to only get the user drawn / shaped creation from all the canvas. There should be a way to "surround" what the user has created and then save it:
By (in the drawing case probably) checking only for the color comparison between the white and the player color;
By, somehow, defining different points that all together would countain the user creation (either drawn or shaped);
Note: In this case I am kind of lost. I have almost no clue of how this could be made. However, I have heard of box2d but I think it was more focused in C or something of that kind? Would it work and how could I do it?
I would finally have the user creation stored and ready to load it in game as an image of a sprite.
I hope I could explain it all correctly. Can someone give me some orientation on this? FYI I am using Phaser.js as js game engine. (sorry for any mistakes, I am not very experienced with this matters).
Hopefully this will get you headed in the right direction:
Instead of drawing to the canvas, create a Phaser bitmapData object and have the user draw to that object. See this example that shows how to draw to a bitmapData object.
If you follow #1, then all of the data that you want will be stored in the bitmapData object, and you can create a Sprite directly from your bitmapData object, e.g.:
// Create a bitmapData object for the user to draw on
var bmd = this.game.make.bitmapData(64, 64);
// code to draw on `bmd` goes here
// Create a Sprite based on the bitmapData from above
var userSprite = this.game.add.sprite(0, 0, bmd);
I decided to day to embark on element and I can say so far it have been nightmare to get it work. All I want is to plot a sine graph. So after good reading I still cannot either get origins nor get it plot. Below is what I have tried (my first time ever with that tag so excuse my ignorance). What makes me wonder is the guy here have it but the codes are hard to understand for beginner like me.
HTML
<!DOCTYPE html>
<html>
<head>
<title>Graphing</title>
<link type="text/css" rel="Stylesheet" href="graph.css" />
<script type="text/JavaScript" src="graph.js" ></script>
</head>
<body>
<canvas id="surface">Canvas not Supported</canvas>
</body>
</html>
CSS
#surface
{
width:300;
height:225;
border: dotted #FF0000 1px;
}
JavScript
window.onload = function()
{
var canvas = document.getElementById("surface");
var context = canvas.getContext("2d");
arr = [0,15, 30,45,60, 90,105, 120, 135, 150, 165, 180 ];
var x=0;
var y = 0;
for(i=0; i<arr.length; i++)
{
angle = arr[i]*(Math.PI/180); //radians
sine = Math.sin(angle);
context.moveTo(x,y);
context.lineTo(angle,sine);
context.stroke();
//set current varibles for next move
x = angle;
y = sine;
}
}
Since the range of sin x is [-1,1], it will only return numbers between -1 and 1, and that means all you will be drawing is a dot on the screen.
Also I see that you have an array ranging from 0 to 180. I believe you are trying to draw the curve with x from 0 degree to 180 degree? You don't really need to do this (anyway 12 points are not enough to draw a smooth line). Just do it with a for loop, with lines being the number of fragments.
First we start off by moving the point to the left of the canvas:
context.moveTo(0, 100 /*somewhere in the middle*/); //initial point
In most cases the first point won't be in the middle. But for sine it is. (You might want to fix it later though.)
for (var i = 0; i < lines; i++) {
//draw line
}
That's the loop drawing the curve. But what should we put inside? Well you can just take the number returned by the sine function and scale it up, flip it upside down, and shift it down half the way. I do that because the coordinate system in JavaScript is 0,0 in the top left instead of in the bottom left.
var sine = Math.sin(i/scale*2)*scale;
context.lineTo(i*frag, -sine+scale);
//i * frag = the position of x scaled up
//-sine + scale = the position of y, flipped, scaled, shifted down
//i/scale*2 = random scale I put in... you might want to figure out the
// correct scale with some math
So that's it. Viola, you have successfully plotted a graph in JavaScript.
Oh yes, don't forget to actually tell it to draw it on the canvas after the for loop has done its job:
context.stroke();
The demo: http://jsfiddle.net/DerekL/hK5rC/
PS: I see that you are trying to resize the canvas using CSS. Trust me, it won't work. :) You will have to define the dimension in HTML.
I am making a loading spinner with html5 canvas. I have my graphic on the canvas but when i rotate it the image rotates off the canvas. How do I tell it to spin the graphic on its center point?
<!DOCTYPE html>
<html>
<head>
<title>Canvas test</title>
<script type="text/javascript">
window.onload = function() {
var drawingCanvas = document.getElementById('myDrawing');
// Check the element is in the DOM and the browser supports canvas
if(drawingCanvas && drawingCanvas.getContext) {
// Initaliase a 2-dimensional drawing context
var context = drawingCanvas.getContext('2d');
//Load the image object in JS, then apply to canvas onload
var myImage = new Image();
myImage.onload = function() {
context.drawImage(myImage, 0, 0, 27, 27);
}
myImage.src = "img/loading.png";
context.rotate(45);
}
}
</script>
</head>
<body>
<canvas id="myDrawing" width="27" height="27">
</canvas>
</body>
</html>
Here is the complete working example:)
<!DOCTYPE html>
<html>
<head>
<title>Canvas Cog</title>
<script type="text/javascript">
var cog = new Image();
function init() {
cog.src = 'data:image/png;base64,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'; // Set source path
setInterval(draw,10);
}
var rotation = 0;
function draw(){
var ctx = document.getElementById('myCanvas').getContext('2d');
ctx.globalCompositeOperation = 'destination-over';
ctx.save();
ctx.clearRect(0,0,27,27);
ctx.translate(13.5,13.5); // to get it in the origin
rotation +=1;
ctx.rotate(rotation*Math.PI/64); //rotate in origin
ctx.translate(-13.5,-13.5); //put it back
ctx.drawImage(cog,0,0);
ctx.restore();
}
init();
</script>
</head>
<body>
<canvas width="27" height="27" id="myCanvas"></canvas>
</body>
</html>
rotate turns the canvas(?) around your current position, which is 0, 0 to start. you need to "move" to your desired center point, which you can accomplish with
context.translate(x,y);
after you move your reference point, you want to center your image over that point. you can do this by calling
context.drawImage(myImage, -(27/2), -(27/2), 27, 27);
this tells the browser to start drawing the image from above and to the left of your current reference point, by have the size of the image, whereas before you were starting at your reference point and drawing entirely below and to the right (all directions relative to the rotation of the canvas).
since your canvas is the size of your image, your call to translate will use the same measurement, (27/2), for x and y coordinates.
so, to put it all together
// initialization:
context.translate(27/2, 27/2);
// onload:
context.rotate(Math.PI * 45 / 180);
context.drawImage(myImage, -(27/2), -(27/2), 27, 27);
edit: also, rotation units are radians, so you'll need to translate degrees to radians in your code.
edits for rearranging stuff.
For anyone else looking into something like this, you might want to look at this script which does exactly what was originally being requested:
http://projects.nickstakenburg.com/spinners/
You can find the github source here:
https://github.com/staaky/spinners
He uses rotate, while keeping a cache of rectangles which slowly fade out, the older they are.
I find another way to do html loading spinner. You can use sprite sheet animation. This approach can work both by html5 canvas or normal html/javascript/css. Here is a simple way implemented by html/javascript/css.
It uses sprite sheet image as background. It create a Javascript timer to change the background image position to control the sprite sheet animation. The example code is below. You can also check the result here: http://jmsliu.com/1769/html-ajax-loading-spinner.html
<html>
<head><title></title></head>
<body>
<div class="spinner-bg">
<div id="spinner"></div>
</div>
<style>
.spinner-bg
{
width:44px;
height:41px;
background: #000000;
}
#spinner
{
width: 44px;
height: 41px;
background:url(./preloadericon.png) no-repeat;
}
</style>
<script>
var currentbgx = 0;
var circle = document.getElementById("spinner");
var circleTimer = setInterval(playAnimation, 100);
function playAnimation() {
if (circle != null) {
circle.style.backgroundPosition = currentbgx + "px 0";
}
currentbgx -= 44; //one frame width, there are 5 frame
//start from 0, end at 176, it depends on the png frame length
if (currentbgx < -176) {
currentbgx = 0;
}
}
</script>
</body>