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I am creating a Javascript game. It is about a guy who stands on top of the world. I already have an earth and now I need to rotate it but when I rotate it it also changes it place.
As you can see the earth rotates but it also changes its place. I want it to rotate just like the rotate keyframes from css. Any thoughts?
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="Style.css"/>
</head>
<body onload="draw()">
<canvas id="canvas"></canvas>
</body>
<script>
var ctx = document.getElementById("canvas").getContext('2d');
var canvas = document.getElementById("canvas");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
setInterval(draw, 10);
function draw() {
var img = new Image();
img.onload = function(){
ctx.rotate(1*Math.PI/180);
ctx.drawImage(img,canvas.width/2-200,canvas.height/2-100,300,300);
};
img.src = "earth.png";
}
</script>
</html>
The code doesn't work because it cant load the image because i have it downloaded but now you guys have the code so you can see the problem.
A quicker way that avoids having to use save and restore.
If you are drawing 100's or 1000's of images (such as for games) the use of save and restore can make the difference between playable and not. In some situations the restore call can drop the frame rate for a nice 60fps to less than 10fps.
Always be careful when using save and restore, making sure you don't have large patterns, or filters ( if supported), complex gradients, or detailed fonts when you save. You are better to remove these thing before you do the save and restore if you plan to do many of them
For single images it does not matter and the previous answer is the best solution.
General purpose sprite render with scales rotation and fade
// draws a image centered at x,y scaled by sx,sy rotate (r in radians) and faded by alpha (0-1)and
function drawImage(image,x,y,sx,sy,r,alpha){ //
ctx.setTransform(sx,0,0,sy,x,y);
ctx.rotate(r);
ctx.globalAlpha = alpha;
ctx.drawImage(image,-image.width/2,-image.height/2);
}
and without fade
function drawImage(image,x,y,sx,sy,r){ //
ctx.setTransform(sx,0,0,sy,x,y);
ctx.rotate(r);
ctx.drawImage(image,-image.width/2,-image.height/2);
}
or if you want to have the default transform after the call
function drawImage(image,x,y,sx,sy,r){ //
ctx.setTransform(sx,0,0,sy,x,y);
ctx.rotate(r);
ctx.drawImage(image,-image.width/2,-image.height/2);
ctx.setTransform(1,0,0,1,0,0);
}
As you may want to render many images in a row you can restore the canvas context with
function restoreContext(){
ctx.globalAlpha = 1;
ctx.setTransform(1,0,0,1,0,0);
}
See this fiddle
HTML
<canvas id="canvas"></canvas>
JavaScript
var ctx = document.getElementById("canvas").getContext('2d');
var canvas = document.getElementById("canvas");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var img;
function draw() {
img = new Image();
img.onload = function(){
setInterval(rotate, 10);
};
img.src = "https://pixabay.com/static/uploads/photo/2013/07/12/13/55/earth-147591_960_720.png";
}
draw();
var i = 0;
function rotate() {
i += 1;
drawRotatedImage(img, 100, 100, 200, 200, i);
}
var TO_RADIANS = Math.PI/180;
function drawRotatedImage(image, x, y, width, height, angle) {
ctx.save();
ctx.translate(x, y);
ctx.rotate(angle * TO_RADIANS);
ctx.drawImage(image, -width/2, -height/2, width, height);
ctx.restore();
}
I'm playing with canvas in HTML5 and Javascript and I have a problem:
I'd like to apply transformations used on the current image to multiple images.
What I did:
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var img = new Image();
img.onload = function() {
//transformation stuff like:
canvas.height = img.height;
canvas.width = img.width;
ctx.drawImage(img, -img.width / 2, -img.height / 2, img.width, img.height);
ctx.beginPath();
ctx.lineTo(42, 42);
ctx.stroke();
ctx.lineTo(42, 24);
ctx.stroke();
...
ctx.rotate(Math.PI / 2);
...
};
img.src = //base64Img;
So I will apply a lot of transformations like draw some lines, crop, zoomIn etc...
How can I apply this to multiple files (more than 200) once (when these transformations are done) ?
Obviously, it will be done in multiples functions like a function to rotate, to draw a line etc.
Thank you for your help.
Put your transformations, path drawings & image drawing into a function with arguments that tell the function how each image will be treated:
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house32x32transparent.png";
function start(){
// Note: img coordinates are [centerX,centerY] rather than the usual [left,top]
drawTransformedImage(img,25,50,0,.75);
drawTransformedImage(img,75,50,Math.PI*1/6,1);
drawTransformedImage(img,150,50,Math.PI*2/6,2);
drawTransformedImage(img,225,50,Math.PI*3/6,1);
drawTransformedImage(img,275,50,Math.PI*4/6,.5);
}
function drawTransformedImage(img,cx,cy,radAngle,scale){
// save incoming styling
var lw=ctx.lineWidth;
var ss=ctx.strokeStyle;
// cache often used half-sizes
var iwHalf=img.width/2;
var ihHalf=img.height/2;
ctx.lineWidth=2;
// do the specified transformations
ctx.translate(cx,cy);
ctx.rotate(radAngle);
ctx.scale(scale,scale);
// draw the image
ctx.drawImage(img,-iwHalf,-ihHalf);
// stroke some paths
ctx.beginPath();
ctx.moveTo(-iwHalf,ihHalf);
ctx.lineTo(-iwHalf,-ihHalf);
ctx.strokeStyle='orange';
ctx.stroke();
ctx.beginPath();
ctx.moveTo(-iwHalf,-ihHalf);
ctx.lineTo(+iwHalf,-ihHalf);
ctx.strokeStyle='blue';
ctx.stroke();
// clean up: reset transformations and stylings
ctx.setTransform(1,0,0,1,0,0);
ctx.lineWidth=lw;
ctx.strokeStyle=ss;
}
body{ background-color: white; }
#canvas{border:1px solid red;}
<canvas id="canvas" width=300 height=150></canvas>
Transforming an Image
Your example does not show a image being transformed, making your question unclear.
The transform is independent of the image, it is used to transform pixel coordinates drawn onto the canvas. It does not affect the image. You can set the transform and then draw the 200 images and they will all have the same transformation applied when their content is rendered to the canvas.
Code example
To transform the image you must create a canvas, set the transform, then render the image onto that canvas. The canvas is now the transformed image.
An example of transforming an image.
var mirrorImage = function (image, vertical, horizontal) {
var imageResult, ctx, vF, hF, posX, posY;
// create new canvas
imageResult = document.createElement("canvas");
// set the pixels size to match the image
imageResult.width = image.width;
imageResult.height = image.height;
// create a drawable surface
ctx = imageResult.getContext("2d");
// create the mirror transformation
hF = horizontal ? -1, 0;
vF = vertical ? -1 : 0;
posX = horizontal ? image.width, 0;
posY = vertical ? image.height : 0;
// Apply the transform to the new image
ctx.setTransform(hF, 0, 0, vF, posX, posY);
// transform the original image by drawing it onto the new
ctx.drawImage(image, 0, 0);
// return the new image.
return imageResult;
}
// create image
var img = new Image();
img.src = "ship.png";
// when loaded transform the image
img.onload = function () {
img = mirrorImage(img, true, true);
// the image has been transformed.
}
To do that to 200 images you have to call mirrorImage (or what ever you are doing) for each image.
Say I have a canvas that's a rectangle. I want to take that canvas and split it diagonally and be able to manipulate those pieces to do whatever I want.
My end goal is to have a rectangle split diagonally and the 2 pieces animate off screen in opposite directions. I was thinking of doing this entirely within the canvas in an animation loop or converting each segment into an image element and using CSS3 animations to move those pieces. I'm just trying to figure out the best way to do this.
The code, codepen link, and image below are just to illustrate where I want my canvas to be split. You'll see it's not an exact split with equal sides.
http://codepen.io/FranciscoG/pen/YPjzbQ
<div id="container">
<img id="dog" src="http://i.imgur.com/1GUzYh9.jpg" width="375"
height="667">
</div>
<script>
var container = document.getElementById('container');
var dogImg = document.getElementById('dog');
function convertImageToCanvas(image) {
var canvas = document.createElement("canvas");
canvas.width = image.width;
canvas.height = image.height;
canvas.getContext("2d").drawImage(image, 0, 0);
return canvas;
}
function drawLine(canvas) {
var context = canvas.getContext('2d');
context.beginPath();
context.moveTo(0,0);
context.lineTo(345, 0);
context.lineTo(0, 567);
context.lineTo(0,0);
context.stroke();
context.closePath();
return canvas;
};
var newDog = convertImageToCanvas(dogImg);
var divided = drawLine(newDog);
container.innerHTML = "";
container.appendChild(divided)
</script>
You could always use clipping but note that this would involve save/restore calls which is a relative slow business. There has been suggested to get resetClip() included in the specs but it seem to be hard to get the message across to the group why it is needed.
In any case, I would recommend the following approach:
Create an object or function that can reproduce a single mask (path) of one of the half-side of the image (ie. the diagonal line with containing box).
For left half: Draw image, set composite mode to destination-in, draw mask, extract canvas as image
For right half: Draw image, set composite mode to destination-out, draw mask, extract canvas as image
Now put the to images (just use the canvas elements directly) inside a container so that they are stacked on top of each other.
Animate using a transition or animation class.
var img = new Image(375, 667);
img.onload = setup;
img.src = "http://i.imgur.com/1GUzYh9.jpg";
function setup() {
var path = [0,0, 345,0, 0, 567]; // last point not needed..
var left = createCanvas(this, path, "destination-in");
var right = createCanvas(this, path, "destination-out");
var cont = document.getElementById("cont");
cont.appendChild(left);
cont.appendChild(right);
// animate here by setting animation/transition class or using JS:
var x = 0;
(function loop() {
left.style.left = x + "px"; // translate is smoother, but need
right.style.left = -x + "px"; // prefix in some browser. Update as needed..
x-=5; if (x < -400) x = 0;
requestAnimationFrame(loop);
})();
function createCanvas(img, path, mode) {
var canvas = document.createElement("canvas"),
ctx = canvas.getContext("2d");
canvas.width = img.width;
canvas.height = img.height;
// draw image
ctx.drawImage(img, 0, 0);
// create mask
ctx.moveTo(path[0], path[1]);
for(var i = 2; i < path.length; i += 2) ctx.lineTo(path[i], path[i+1]);
ctx.closePath();
// composite mode and create half
ctx.globalCompositeOperation = mode;
ctx.fill();
return canvas
}
}
#cont {
position:relative;width:375px;height:667px;overflow:hidden;
}
#cont>canvas {position:absolute;left:0;right:0;}
<div id="cont"></div>
You can use context.clip to achieive your image-splitting effect
context.clip restricts an image to being drawn withing a specified path.
You can define several of these clipping regions to divide your image into several pieces (paths).
Then in an animation loop, you can clear the canvas and redraw each of these clipping regions with an changing offset. The left clipping region will move (offset) leftward in each loop. The right clipping region will move (offset) rightward in each loop.
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;
var nextTime=0;
var duration=1000/60*3;
var offset=0;
var paths=[];
var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/multple/Dog-With-Cute-Cat.jpg";
function start(){
cw=canvas.width=img.width;
ch=canvas.height=img.height;
paths.push({path:[{x:0,y:0},{x:150,y:0},{x:0,y:ch}],direction:-1});
paths.push({path:[{x:150,y:0},{x:0,y:ch},{x:cw,y:ch},{x:cw,y:0}],direction:1});
requestAnimationFrame(animate);
}
function draw(){
ctx.clearRect(0,0,cw,ch);
for(var i=0;i<paths.length;i++){
var path=paths[i].path;
var offX=offset*paths[i].direction;
ctx.save();
ctx.beginPath();
var pt=path[0];
ctx.moveTo(pt.x+offX,pt.y);
for(var j=1;j<path.length;j++){
var pt=path[j];
ctx.lineTo(pt.x+offX,pt.y);
}
ctx.closePath();
ctx.stroke();
ctx.clip();
ctx.drawImage(img,offX,0);
ctx.restore();
}
}
function animate(time){
if(offset<cw){requestAnimationFrame(animate);}else{log('done');}
if(time<nextTime){return;}
nextTime=time+duration;
draw();
offset++;
}
body{ background-color: ivory; padding:10px; }
#canvas{border:1px solid red;}
<canvas id="canvas" width=300 height=300></canvas>
I am making an HTML5 canvas game, and I wish to rotate one of the images.
var link = new Image();
link.src='img/link.png';
link.onload=function(){
ctx.drawImage(link,x,y,20,20); // draws a chain link or dagger
}
I wish to rotate this image. The standard way of rotating image was to set a rotation on the canvas context object. However, that rotates the entire game! I don't want to do that, and only wish to rotate this one sprite. How do I do that?
Use .save() and .restore() (more information):
link.onload=function(){
ctx.save(); // save current state
ctx.rotate(Math.PI); // rotate
ctx.drawImage(link,x,y,20,20); // draws a chain link or dagger
ctx.restore(); // restore original states (no rotation etc)
}
You might want to put a translate(); there because the image is going to rotate around the origin and that is in the top left corner by default so you use the translate(); to change the origin.
link.onload=function(){
ctx.save();
ctx.translate(x, y); // change origin
ctx.rotate(Math.PI);
ctx.drawImage(link,-10,-10,10,10);
ctx.restore()
}
Your original "solution" was:
ctx.save();
ctx.translate(x,y);
ctx.rotate(-this.angle + Math.PI/2.0);
ctx.translate(-x, -y);
ctx.drawImage(this.daggerImage,x,y,20,20);
ctx.restore();
However, it can be made more efficient (with no save or restore) by using this code:
ctx.translate(x,y);
ctx.rotate(-this.angle + Math.PI/2.0);
ctx.drawImage(this.daggerImage,x,y,20,20);
ctx.rotate(this.angle - Math.PI/2.0);
ctx.translate(-x, -y);
Look at my solution. It's full example and the easiest to understand.
var drawRotate = (clockwise) => {
const degrees = clockwise == true? 90: -90;
let canvas = $('<canvas />')[0];
let img = $(".img-view")[0];
const iw = img.naturalWidth;
const ih = img.naturalHeight;
canvas.width = ih;
canvas.height = iw;
let ctx = canvas.getContext('2d');
if(clockwise){
ctx.translate(ih, 0);
} else {
ctx.translate(0, iw);
}
ctx.rotate(degrees*Math.PI/180);
ctx.drawImage(img, 0, 0);
let rotated = canvas.toDataURL();
img.src = rotated;
}
Here i made a working example from one of my games. u can get the image from Here.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset=utf-8 />
<title>Test</title>
</head>
<body>
<canvas id="canvas" width="100" height="100"></canvas>
<script type="text/javascript">
var ctx = document.getElementById('canvas').getContext('2d');
var play = setInterval('Rotate()',16);
var i = 0;
var shipImg = new Image();
shipImg.src = 'ship.png';
function Rotate() {
ctx.fillStyle = '#000';
ctx.fillRect(0,0,100,100);
ctx.save();
ctx.translate(50, 50);
ctx.rotate(i / 180 / Math.PI);
ctx.drawImage(shipImg, -16, -16);
ctx.restore();
i += 10;
};
</script>
</body>
</html>
I ended up having to do:
ctx.save();
ctx.translate(x,y);
ctx.rotate(-this.angle + Math.PI/2.0);
ctx.translate(-x, -y);
ctx.drawImage(this.daggerImage,x,y,20,20);
ctx.restore();
I'm trying to figure out how to rotate a single object on an html 5 canvas.
For example: http://screencast.com/t/NTQ5M2E3Mzct - I want each one of those cards to be rotated at a different degree.
So far, all I've seen are articles and examples that demonstrate ways to rotate the entire canvas. Right now, I'm guessing I'll have to rotate the canvas, draw an image, and then rotate the canvas back to it's original position before drawing the second image. If that's the case, then just let me know! I just have a feeling that there's another way.
Anyone have any idea?
I ran into the same problem in a recent project (where I kicked rotating aliens all over the place). I just used this humble function that does the same thing and can be used the same way as ctx.rotate but can be passed an angle. Works fine for me.
function drawImageRot(img,x,y,width,height,deg){
// Store the current context state (i.e. rotation, translation etc..)
ctx.save()
//Convert degrees to radian
var rad = deg * Math.PI / 180;
//Set the origin to the center of the image
ctx.translate(x + width / 2, y + height / 2);
//Rotate the canvas around the origin
ctx.rotate(rad);
//draw the image
ctx.drawImage(img,width / 2 * (-1),height / 2 * (-1),width,height);
// Restore canvas state as saved from above
ctx.restore();
}
Yay, my first answer!
Unfortunately in the HTML5 canvas element you can't rotate individual elements.
Animation works like drawing in MS Paint: You draw something, make a screen.. use the eraser to remove some stuff, draw something differently, make a screen.. Draw something else on top, make a screen.. etc etc.
If you have an existing item on the canvas - you'll have to erase it ( use ctx.fillRect() or clearRect() for example ), and then draw the rotated object.
If you're not sure how to rotate it while drawing in the first place:
ctx.save();
ctx.rotate(0.17);
// draw your object
ctx.restore();
To rotate a individual object you have to set the transformation matrix. This is really simple:
var context = document.getElementById('pageCanvas').getContext('2d');
var angle = 0;
function convertToRadians(degree) {
return degree*(Math.PI/180);
}
function incrementAngle() {
angle++;
if(angle > 360) {
angle = 0;
}
}
function drawRandomlyColoredRectangle() {
// clear the drawing surface
context.clearRect(0,0,1280,720);
// you can also stroke a rect, the operations need to happen in order
incrementAngle();
context.save();
context.lineWidth = 10;
context.translate(200,200);
context.rotate(convertToRadians(angle));
// set the fill style
context.fillStyle = '#'+Math.floor(Math.random()*16777215).toString(16);
context.fillRect(-25,-25,50,50);
context.strokeRect(-25,-25,50,50);
context.restore();
}
// Ideally use getAnimationFrame but for simplicity:
setInterval(drawRandomlyColoredRectangle, 20);
<canvas width="1280" height="720" id="pageCanvas">
You do not have a canvas enabled browser
</canvas>
Basically, to make an object rotate properly without having other shape rotating around, you need to:
save the context: ctx.save()
move the pivot point to the desired location: ctx.translate(200, 200);
rotate: context.rotate(45 * Math.PI / 180);
draw the shape, sprite, whatever: ctx.draw...
reset the pivot: ctx.translate(-200, -200);
restore the context to its original state: ctx.restore();
function spinDrawing() {
ctx.save();
ctx.translate(200, 200);
context.rotate(45 * Math.PI / 180);
ctx.draw //your drawing function
ctx.translate(-200, -200);
ctx.restore();
}
Caveats: After you translating , the origin of the canvas changed, which means when you drawing the shape, the coordinate of the shape should be aligned accordingly.
Shapes drawn outside the list mentioned above won´t be affected. I hope it helps.
This html/javascript code might shed some light on the matter:
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="233" height="233" style="border:1px solid #d3d3d3;">
your browser does not support the canvas tag </canvas>
<script type="text/javascript">
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
var canvasWidth=233;
var canvasHeight=233;
var rectWidth=100;
var rectHeight=150;
var x=30;
var y=30;
var translateX= x+(rectWidth/2);
var translateY= y+(rectHeight/2);
ctx.fillRect(x,y,rectWidth,rectHeight);
ctx.translate(translateX,translateY);
ctx.rotate(5*Math.PI/64); /* just a random rotate number */
ctx.translate(-translateX,-translateY);
ctx.fillRect(x,y,rectWidth,rectHeight);
</script>
</body>
</html>
I find it helpful to see the math related to rotating, I hope this was helpful to you too.
<!DOCTYPE html>
<html>
<body>
<canvas id="myCanvas" width="500" height="450" style="border:1px solid #d3d3d3;">
</canvas>
<Button id = "right" onclick = "rotateRight()">Right</option>
<Button id = "left" onclick = "rotateLeft()">Left</option>
<script src = "zoom.js">
</script>
<script>
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
createRect();
function rotateRight()
{
ctx.save();
ctx.clearRect(0,0,500,450);
ctx.translate(c.width/2,c.height/2);
ctx.rotate(10*Math.PI/180 );
ctx.translate(-c.width/2,-c.height/2);
createRect();
}
function rotateLeft()
{
ctx.save();
ctx.clearRect(0,0,500,450);
ctx.translate(c.width/2,c.height/2);
ctx.rotate(-10*Math.PI/180 );
ctx.translate(-c.width/2,-c.height/2);
createRect();
}
function createRect()
{
ctx.beginPath();
ctx.fillStyle = "#AAAA00";
ctx.fillRect(250,250,90,50);
}
</script>
</body>
</html>
To rotate an object you can use rotate() method. Here the example how to rotate a rectangular object to 135 degrees of clockwise.
<script>
var canvas = document.getElementById('Canvas01');
var ctx = canvas.getContext('2d');
var rectWidth = 100;
var rectHeight = 50;
//create line
ctx.strokeStyle= '#ccc';
ctx.beginPath();
ctx.moveTo(canvas.width / 2, 0);
ctx.lineTo(canvas.width / 2, canvas.height);
ctx.stroke();
ctx.closePath();
ctx.beginPath();
ctx.moveTo(0, canvas.height/2);
ctx.lineTo(canvas.width, canvas.height/2);
ctx.stroke();
ctx.closePath();
// translate ctx to center of canvas
ctx.translate(canvas.width / 2, canvas.height / 2);
// rotate the rect to 135 degrees of clockwise
ctx.rotate((Math.PI / 180)*135);
ctx.fillStyle = 'blue';
ctx.fillRect(0, 0, rectWidth, rectHeight);
</script>
</body>
Here the demo and you can try yourself: http://okeschool.com/examples/canvas/html5-canvas-rotate
I found this question because I had a bunch of stuff on a canvas, drawn with canvas lines, painstakingly, and then decided some of them should be rotated. Not wanting to do a whole bunch of complex stuff again I wanted to rotate what I had. A simple solution I found was this:
ctx.save();
ctx.translate(x+width_of_item/2,y+height_of_item/2);
ctx.rotate(degrees*(Math.PI/180));
ctx.translate(-(x+width_of_item/2),-(y+height_of_item/2));
// THIS IS THE STUFF YOU WANT ROTATED
// do whatever it is you need to do here, moveto and lineto is all i used
// I would expect anything to work. use normal grid coordinates as if its a
// normal 0,0 in the top left kind of grid
ctx.stroke();
ctx.restore();
Anyway - it might not be particularly elegant but its a dead easy way to rotate one particular element onto your canvas.
Look at all those rotated elements!