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HTML5 Canvas moving object to mouse click position
(1 answer)
Closed 6 years ago.
I was wondering is it possible to move a shape on the canvas to specific coordinates on the canvas from another set of coordinates. In this case is it possible to get the location of a mouse click and create an object that moves to that point over a specific amount of time? Thanks for your help in advance!
<canvas id="canvas"></canvas>
<script>
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var x2=100,y2=100;
var dx=0,dy=0;
var counter=10;
canvas.width = canvas.height = 256;
var shape = {x:100, y:100, width : 50, height : 30};
function clear() {
ctx.fillStyle = 'rgba(255, 255, 255, 0.3)';
ctx.fillRect(0,0,canvas.width,canvas.height);
}
function draw(){
if(counter>0){
shape.x=shape.x+dx;
shape.y=shape.y+dy;
ctx.clearRect(0,0,256,256);
ctx.fillStyle = "red";
ctx.strokeStyle = "black";
ctx.fillRect(shape.x, shape.y, shape.width, shape.height);
ctx.strokeRect(shape.x, shape.y, shape.width,shape.height);
counter--;
setTimeout(draw,20)
}
}
canvas.addEventListener("click", function(e) {
clear();
x2=e.clientX;
y2=e.clientY;
dx=(x2-shape.x)/10;
dy=(y2-shape.y)/10;
counter=10;
draw();
});
draw();
</script>
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'm developing web app using canvas and I made three. canvas, canvas_panorama and canvas_image.
First one is something like main canvas, conteiner for the others. canvas_panorama is a background for canvas_image.
After canvas is right clicked, I'm computing angle to rotate canvas_image:
function getAngle( e, pw /*canvas*/ ){
var offset = pw.offset();
var center_x = (offset.left) + ($(pw).width() / 2);
var center_y = (offset.top) + ($(pw).height() / 2);
var mouse_x = e.pageX;
var mouse_y = e.pageY;
var radians = Math.atan2(mouse_x - center_x, mouse_y - center_y);
angle = radians;
}
After I have an angle I'm trying to rotate canvas_image like this:
function redraw(){
var p1 = ctx.transformedPoint(0,0);
var p2 = ctx.transformedPoint(canvas.width,canvas.height);
ctx.clearRect( p1.x, p1.y, p2.x-p1.x, p2.y-p1.y );
canvas_image_ctx.drawImage(image_img, 0, 0, 150, 150);
canvas_panorama_ctx.drawImage(panorama_img, 0, 0, 600, 300);
canvas_panorama_ctx.drawImage(canvas_image, 20, 20);
// rotate panorama_img around its center
// x = x + 0.5 * width
// y = y + 0.5 * height
canvas_panorama_ctx.translate(95, 95);
canvas_panorama_ctx.rotate(angle);
// translate to back
canvas_panorama_ctx.translate(-95, -95);
ctx.drawImage(canvas_panorama, 0, 0);
}
But this rotates both canvas_image and canvas_panorama. It should only rotate canvas_image
JSFiddle to show you my problem
I think you are confusing yourself with this idea of multiple canvases.
Once in the drawImage() method, every of your canvases are just images, and could be just one or even just plain shapes.
Transformation methods do apply to the canvas' context's matrix, and will have effect only if you do some drawing operations when they are set.
Note : To reset your context matrix, you can either use save(); and restore() methods which will also save all other properties of your context, so if you only need to reset the transform, then it's preferred to simply reset the transformation matrix to its default : ctx.setTransform(1,0,0,1,0,0).
Here is a simplified example to make things clearer :
var ctx = canvas.getContext('2d');
// a single shape, with the border of the context matrix
var drawRect = function(){
ctx.beginPath();
ctx.rect(10, 10, 50, 20);
ctx.fill();
ctx.stroke();
ctx.beginPath();
ctx.rect(0, 0, canvas.width, canvas.height);
ctx.stroke();
};
// set the color of our shapes
var gradient = ctx.createLinearGradient(0,0,70,0);
gradient.addColorStop(0,"green");
gradient.addColorStop(1,"yellow");
ctx.fillStyle = gradient;
// here comes the actual drawings
//we don't have modified the transform matrix yet
ctx.strokeStyle = "green";
drawRect();
// here we translate of 100px then we do rotate the context of 45deg
ctx.translate(100, 0)
ctx.rotate(Math.PI/4)
ctx.strokeStyle = "red";
drawRect();
// reset the matrix
ctx.setTransform(1,0,0,1,0,0);
// here we move of 150px to the right and 25px to the bottom
ctx.translate(150, 25)
ctx.strokeStyle = "blue";
drawRect();
// reset the matrix
ctx.setTransform(1,0,0,1,0,0);
<canvas id="canvas" width="500" height="200"></canvas>
In your code, you are setting the transformations on the canvas that does represent your image, and you do draw every of your canvases at each call.
What you want instead, is to set the transformation on the main canvas only, and draw the non-transformed image :
var main_ctx = canvas.getContext('2d');
var img_canvas = canvas.cloneNode();
var bg_canvas = canvas.cloneNode();
var angle = 0;
// draw on the main canvas, and only on the main canvas
var drawToMain = function(){
// first clear the canvas
main_ctx.clearRect(0,0,canvas.width, canvas.height);
// draw the background image
main_ctx.drawImage(bg_canvas, 0,0);
// do the transforms
main_ctx.translate(img_canvas.width/2, img_canvas.height/2);
main_ctx.rotate(angle);
main_ctx.translate(-img_canvas.width/2, -img_canvas.height/2);
// draw the img with the transforms applied
main_ctx.drawImage(img_canvas, 0,0);
// reset the transforms
main_ctx.setTransform(1,0,0,1,0,0);
};
// I changed the event to a simple onclick
canvas.onclick = function(e){
e.preventDefault();
angle+=Math.PI/8;
drawToMain();
}
// a dirty image loader
var init = function(){
var img = (this.src.indexOf('lena')>0);
var this_canvas = img ? img_canvas : bg_canvas;
this_canvas.width = this.width;
this_canvas.height = this.height;
this_canvas.getContext('2d').drawImage(this, 0,0);
if(!--toLoad){
drawToMain();
}
};
var toLoad = 2;
var img = new Image();
img.onload = init;
img.src = "http://pgmagick.readthedocs.org/en/latest/_images/lena_scale.jpg";
var bg = new Image();
bg.onload = init;
bg.src = 'http://www.fnordware.com/superpng/pnggradHDrgba.png';
<canvas id="canvas" width="500" height="300"></canvas>
When I add
ctx.addEventListener('mousedown', onDown, false);
The canvas drawing (background and shapes) disappear and the page is blank, and then when I remove this event listener from the code they reappear again. Just wondering why this is happening? Thanks in advance
<script>
var ctx, W, H;
var x = 10;
window.onload = function() {
var canvas = document.getElementById("canvas");
W = window.innerWidth;
H = window.innerHeight;
canvas.width = W;
canvas.height = H;
ctx = canvas.getContext("2d");
ctx.addEventListener('mousedown', onDown, false); //When this is here, canvas drawing disappears, when it's not here canvas drawing reappears again
setInterval(draw, 1);
function draw() {
ctx.globalCompositeOperation = "source-over";
ctx.fillStyle = "#E6E6FF";
ctx.fillRect(0, 0, W, H);
ctx.fillStyle = "black";
ctx.fillRect(x,20,10,10);
ctx.font = "30px Arial";
ctx.fillText("Hello World",10,80);
ctx.fill();
}
}
function onDown(event) {
//where x is found
cx = event.pageX
cy = event.pageY
alert("X,Y ="+cx+','+cy);
}
You can't add an event listener to the canvas's context. You'll need to add it to the canvas itself.
Instead of:
ctx.addEventListener('mousedown', onDown, false);
… do this:
canvas.addEventListener('mousedown', onDown, false);
jsBin demo
use:
ctx.canvas.addEventListener
or:
canvas.addEventListener
cause context is just an Object in which the HTMLElementCanvas lives in.
To spot such errors your-self, the easiest way is to debug your code using Developer Tools, opening the console tab and reading the errors you're shown:
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 am trying to do a simple animation with html5. Please take a look at the link below, through a touch screen device.
https://dl.dropbox.com/u/41627/wipe.html
The problem is as follows : Every time the user touches the screen , a box gets drawn around his finger which animates from small to big. I want just the outer most boundary to be visible and not the rest. I do not want to clear the canvas as I want the state of the rest of the canvas to be preserved.
Images to illustrate the issue:
My code is as follows :
function init() {
var canvas = document.getElementById('c');
var ctx = canvas.getContext('2d');
var img = document.createElement('IMG');
img.onload = function () {
ctx.beginPath();
ctx.drawImage(img, 0, 0);
ctx.closePath();
ctx.globalCompositeOperation = 'destination-out';
}
img.src = "https://dl.dropbox.com/u/41627/6.jpg";
function drawPoint(pointX,pointY){
var grd = ctx.createRadialGradient(pointX, pointY, 0, pointX, pointY, 30);
grd.addColorStop(0, "rgba(255,255,255,.6)");
grd.addColorStop(1, "transparent");
ctx.fillStyle = grd;
ctx.beginPath();
ctx.arc(pointX,pointY,50,0,Math.PI*2,true);
ctx.fill();
ctx.closePath();
}
var a = 0;
var b = 0;
function boxAround(pointX,pointY, a, b) {
ctx.globalCompositeOperation = 'source-over';
ctx.strokeStyle = "black";
ctx.strokeRect(pointX-a, pointY-b, (2*a), (2*b));
ctx.globalCompositeOperation = 'destination-out';
if(a < 100) {
setTimeout(function() {
boxAround(pointX,pointY, a+5, b+5);
}, 20);
}
}
canvas.addEventListener('touchstart',function(e){
drawPoint(e.touches[0].screenX,e.touches[0].screenY);
boxAround(e.touches[0].screenX,e.touches[0].screenY,0 , 0);
},false);
canvas.addEventListener('touchmove',function(e){
e.preventDefault();
drawPoint(e.touches[0].screenX,e.touches[0].screenY);
},false);
You can achieve this effect by either using a second canvas, or even just having the box be a plain <div> element that is positioned over the canvas. Otherwise, there is no way around redrawing your canvas.