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();
Related
Basically what my project does is to fetch a picture from Database, place it into canvas, move it, zoom in and out, this this are working perfectly.
Next step is to rotate the picture and i have no idea what I am doing wrong. In the picture i described how my document looks like when the canvas is accessed. After I rotate the picture, it goes outside the canvas. My code looks like below and i have no idea what I am doing wrong. Thank you
function drawRotated(degrees) {
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.save();
ctx.translate(image.width*0.15,image.height*0.15);
ctx.rotate(degrees * Math.PI / 180);
ctx.translate(-image.width*0.15,-image.height*0.15);
ctx.drawImage(image, 0, 0, image.width*0.15, image.height*0.15);
}
Maybe this is not the answer you are expecting for. I didn't use your code. I hope it helps.
The main idea is to draw the image with the center in the origin of the canvas.
window.onload = function() {
var canvas = document.getElementsByTagName('canvas')[0];
var ctx = canvas.getContext('2d');
canvas.width = 200;
canvas.height = 200;
var gkhead = gk;
gkhead.src = gk.src;
let w = gkhead.width;
let h = gkhead.height;
let x = -w/2;
let y = -h/2;
ctx.drawImage(gkhead,x,y,w,h);
function translateToThePoint(p){
ctx.save();
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.translate(p.x,p.y);
ctx.scale(.25,.25);
ctx.drawImage(gkhead,x,y,w,h);
ctx.restore();
}
function rotate(angleInRad, p){
ctx.save();
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.translate(p.x,p.y);
ctx.rotate(angleInRad);
ctx.scale(.25,.25);
ctx.drawImage(gkhead,x,y,w,h);
ctx.restore();
}
let p = {x:canvas.width/2,y:canvas.height/2}
//translateToThePoint(p);
rotate(-Math.PI/10,p);
}
canvas {
border:1px solid
}
<canvas id="canvas">
<img id="gk" src='https://www.warrenphotographic.co.uk/photography/cats/38088.jpg' />
</canvas>
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 am trying to figure out how one can detect if the user's mouse hits a line on an HTML 5 canvas with jQuery.
Here is the code that generates the canvas lines:
<canvas id="myCanvas" width="400" height="400" style="border:1px solid #c3c3c3;">
Your browser does not support the canvas element.
</canvas>
<script type="text/javascript" src="js/jquery-1.4.2.min.js"></script>
<script type="text/javascript">
window.onload = function(){
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.moveTo(40,0);
ctx.lineTo(40,360);
ctx.stroke();
ctx.moveTo(80,400);
ctx.lineTo(80,40);
ctx.stroke();
ctx.moveTo(120,0);
ctx.lineTo(120,360);
ctx.stroke();
ctx.moveTo(160,400);
ctx.lineTo(160,40);
ctx.stroke();
};
</script>
I'm using a modified jQuery script that I actually found in another question on here, but now I can't figure out how to detect the line, mainly the difference in color from white to black, in the canvas. I know that this can be done with images, but I haven't seen anyone with something like this.
I guess my real question is, is there a way to detect color changes on a canvas element with jQuery?
Its possible to do with javascript. In fact you aren't using any jQuery in your example above. An easy way to do it is by grabbing the pixel data from the canvas, and checking the alpha at the specified x and y position. If the alpha isn't set to 0, then you have something drawn on the canvas. Below is a function I put together real quick that does that.
Live Demo
var canvas = document.getElementById("canvas"),
ctx = canvas.getContext("2d"),
width = 400;
height = 400;
canvas.width = canvas.height = 200;
// draw
ctx.moveTo(40, 0);
ctx.lineTo(40, 360);
ctx.stroke();
ctx.moveTo(80, 400);
ctx.lineTo(80, 40);
ctx.stroke();
ctx.moveTo(120, 0);
ctx.lineTo(120, 360);
ctx.stroke();
ctx.moveTo(160, 400);
ctx.lineTo(160, 40);
ctx.stroke();
function detectLine(x, y) {
var imageData = ctx.getImageData(0, 0, width, height),
inputData = imageData.data,
pData = (~~x + (~~y * width)) * 4;
if (inputData[pData + 3]) {
return true;
}
return false;
}
canvas.addEventListener("mousemove", function(e){
var x = e.pageX,
y = e.pageY;
console.log(detectLine(x, y));
});
console.log(detectLine(40, 100));
console.log(detectLine(200, 200));
I need to rotate an image before loading it into a canvas.
As far as I know, I cant rotate it using the canvas.rotate(), since that rotates the entire scene.
Is there a good JS way to rotate an image? [not the browser dependent ways]
not exactly, you can save the scene, rotate image then restore scene:
var canvas = document.getElementById('canvas');
canvas.width = 600;
canvas.height = 400;
var ctx = canvas.getContext('2d');
var image = new Image();
image.src = 'https://www.google.ro/images/srpr/logo3w.png';
drawRotatedImage(image, 275, 95, 25);
function drawRotatedImage(image, x, y, angle) {
ctx.save();
ctx.translate(x, y);
ctx.rotate(angle * (Math.PI/180));
ctx.drawImage(image, -(image.width/2), -(image.height/2));
ctx.restore();
}
JSFiddle Example
well for u can use a css property transform to rotate, scale and translate html elements instead of using canvas for this you should use transform="rotate(xdeg)" if you want to rotate the image x degrees for continuously rotating the image use the following code.
see this your code
<html>
<img id="t1" src="1.png">
</html>
and this is your javascript code
<script>
var im;
var w,h;
var t=0;
window.onload=function()
{
im=document.getElementById('t1');
w=im.width;
h=im.height;
im.style.transform=im.style.webkitTransform|im.style.mozTransform|im.style.oTransform|i m.style.transform;
update();
};
function update()
{
im.style.transform="rotate("+t+"deg)";
t+=10;
setTimeout("update()",100);
}
</script>
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!