var canvas;
var context;
var isDrawing = false;
window.onload = function()
{
canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
canvas.width=window.innerWidth;
canvas.height=window.innerHeight;
canvas.addEventListener("mousemove", putPoint);
canvas.addEventListener("mousedown", engage);
canvas.addEventListener("mouseup", disengage);
canvas.addEventListener("mouseout", disengage);
context.lineWidth = 2*radius;
context.lineJoin = context.lineCap = 'round';
};
var radius=0.5;
var engage = function(e)
{
isDrawing = true;
putPoint(e)
}
var disengage = function()
{
isDrawing = false;
context.beginPath();
}
var putPoint=function (e)
{
if(isDrawing)
{
context.lineTo(e.clientX-canvas.offsetLeft, e.clientY-canvas.offsetTop);
context.stroke();
context.beginPath();
context.arc(e.clientX-canvas.offsetLeft, e.clientY-canvas.offsetTop, radius, 0, Math.PI*2);
context.fill();
context.beginPath();
context.moveTo(e.clientX-canvas.offsetLeft, e.clientY-canvas.offsetTop);
}
}
body
{
margin: 2px;;
}
canvas
{
border: 1px solid black;
display:block;
}
<!DOCTYPE html>
<html lang="pl">
<head>
<meta charset="utf-8">
<title> Drawing app </title>
<link href="style.css" rel="stylesheet">
<script src="script2.js"> </script>
</head>
<body>
<canvas id="canvas" width="1900" height="1000"> Your browser doesn't support canvas. </canvas>
</body>
</html>
This is my code. Please try draw something. You should see a lot of pixels.
It looks awful. I would like to line looked like this:https://sketch.io/sketchpad/. Please set there 1px and check it. It's beautiful, smooth line without pixels. I would like to achieve it.
Here is nice drawing: http://codepen.io/kangax/pen/zofsp.
But:
- Every time you draw a new path - > canvas is cleaning. It is caused by 26th line of code.
- When I delete it ( I mean 26th line of code ) drawing breaks :c
What I've tried?
-shadows
-gradients
-ctx.translate(0.5,0.5);
-bezier curve
And it doesen't work.
I suppose that beautiful lines I can obtain using this: ctx.clearRect(x1,y1,x2,y2).
But I have no ideas how to use it :c
I am going to create drawing app so I need smooth lines.
Mouse data is always a but rough and there are many ways that you can smooth it. The holy grail for line smoothing is a bezier fit, but I have yet to work out how to do that in real time.
The next best thing is optimising and smoothing the line to an appox fit..
Rather than write the answer out again see the following anwser https://stackoverflow.com/a/33882382/3877726
It provides a way to set the optimization and smoothing from none (sometimes you want the bumps and lumps) all the way to super smooth..
Related
So, I have tried attempting this myself and have searched heavily online and I can't seem to solve this particular issue. I am attempting to make a very simple effect that looks like a very basic water ripple. I intend for the user to be able to click somewhere on the canvas, and for an empty circle (with a black stroke) to appear where the mouse has clicked (starting at a radius of zero), and continuously expand the radius as an animation.
I currently have this code:
<!DOCTYPE html>
<html>
<head>
<!-- Search Engine Optimisation (SEO) -->
<title> Ripple </title>
<meta description="Codelab assignment 3">
<meta keywords="Uni, assignment, ripple, interactive, discovery">
<!-- End of Metadata -->
<!-- Links -->
<link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>
<canvas id="myCanvas" width="1024" height="768" style="border: 1px solid"></canvas>
</body>
<script type="text/javascript">
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
var canvasWidth = canvas.width;
var canvasHeight = canvas.height;
var radius = 0;
//Have a rectangle fill the canvas and add a hit region
//Call the ripple function from the rectangle function
//Track mouse position in rectangle
function ripple(e) {
// ctx.clearRect(0, 0, canvasWidth, canvasHeight);
ctx.beginPath();
ctx.arc(e.clientX,e.clientY,radius,0,2*Math.PI);
//ctx.closePath();
ctx.stokeStyle = "black";
ctx.stroke();
radius++;
requestAnimationFrame(ripple);
}
canvas.addEventListener('mousedown', ripple);
</script>
</html>
This is what it currently does:
Screenshot
I really appreciate any help!
You'd have to pass the mouse event when calling the ripple function through requestAnimationFrame.
also, you'll need to set the radius to 0 and clear running animation frame (if any) on mouse click
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var canvasWidth = canvas.width;
var canvasHeight = canvas.height;
var radius = 0;
var rAF;
function ripple(e) {
ctx.clearRect(0, 0, canvasWidth, canvasHeight);
ctx.beginPath();
ctx.arc(e.offsetX, e.offsetY, radius, 0, 2 * Math.PI);
ctx.stokeStyle = "black";
ctx.stroke();
radius++;
rAF = requestAnimationFrame(function() {
ripple(e);
});
}
canvas.addEventListener('mousedown', function(e) {
if (rAF) cancelAnimationFrame(rAF);
radius = 0;
ripple(e);
});
body{margin:10px 0 0 0;overflow:hidden}canvas{border:1px solid #ccc}
<canvas id="canvas" width="635" height="208"></canvas>
note: use e.offsetX and e.offsetY to get proper mouse coordinates relative to canvas.
I have just started looking into html5 and the canvas element and have been trying to create a simple page that rotates an image clockwise and anti clockwise on button clicks. I managed to get something working but i tested it on ie10 and the image is not showing up, just the blank grey canvas. I can only test on ie10 so not sure if this effects other versions too. My full code is:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
</head>
<body>
<!-- Canvas Element -->
<canvas id="canvas" width="500" height="500" style="background-color: #EAEAEA;">
</canvas>
<!-- Rotate Buttons -->
<h2>Rotate</h2>
<button onclick="rotate('c')">Clockwise</button>
<button onclick="rotate('a')">Anti-Clockwise</button>
<button onclick="rotate('r')">Reset</button>
<script type="text/javascript">
const FPS = 30;
var imagePosX = 90;
var imagePosY = 143;
var imageRot = 0;
var image = new Image();
image.src = "sample.jpg";
var canvas = null;
var context2D = null;
window.onload = startup;
function startup(){
canvas = document.getElementById('canvas');
context2D = canvas.getContext('2d');
setInterval(draw, 500 / FPS);
}
function rotate(d){
setInterval(draw(d), 500 / FPS);
}
function draw(d){
if (d=='a'){imageRot -= 10;}
if (d=='c'){imageRot += 10;}
if (d=='r'){imageRot = 0;}
context2D.clearRect(0, 0, canvas.width, canvas.height);
context2D.save();
context2D.translate(imagePosX+(image.width/2), imagePosY+(image.height/2));
context2D.rotate(imageRot * Math.PI / 180);
// optional shadow
context2D.shadowBlur = 15;
context2D.shadowColor = "rgb(0, 0, 0)";
//
context2D.drawImage(image, 0, 0, image.width, image.height, -(image.width/2), -(image.height/2), image.width, image.height);
context2D.restore();
}
</script>
</body>
</html>
Screenshot of how it should look (and looks in chrome/safari/firefox etc):
Screenshot for ie10:
Can anyone help with what is causing this?
IE 10 doesn't support const. Change it to var. That at least will be one reason for it not working.
Also, the debugger (which is not that amazing in IE10) is still your friend. We'll call him 'semi-friend'. Use him. What does he say?
Basically, a user uploads a picture and then can paint on it, and save the result. Another user can then view the photo and if they click in the same area as painted, something happens.
So user 1 can make an area click-able for user 2 by drawing on the photo.
now the upload bit is fine, and painting with help from a tutorial and example I've got sussed out. But defining what area is click-able is a bit harder. For something like a rectangle its easy enough, I made an example.
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
var button = new Object();
button.x = 50;
button.y = 50;
button.width = 50;
button.height = 50;
button.rgb = "rgb(0, 0, 255)";
function drawbutton(buttonobject)
{
context.fillStyle = buttonobject.rgb;
context.fillRect (buttonobject.x, buttonobject.y, buttonobject.width, buttonobject.height);
context.strokeRect(buttonobject.x, buttonobject.y, buttonobject.width, buttonobject.height);
}
drawbutton(button);
function checkIfInsideButtonCoordinates(buttonObj, mouseX, mouseY)
{
if(((mouseX > buttonObj.x) && (mouseX < (buttonObj.x + buttonObj.width))) && ((mouseY > buttonObj.y) && (mouseY < (buttonObj.y + buttonObj.height))))
return true;
else
return false;
}
$("#myCanvas").click(function(eventObject) {
mouseX = eventObject.pageX - this.offsetLeft;
mouseY = eventObject.pageY - this.offsetTop;
if(checkIfInsideButtonCoordinates(button, mouseX, mouseY))
{
button.rgb = "rgb(0, 255, 0)";
drawbutton(button);
} else {
button.rgb = "rgb(255, 0, 0)";
drawbutton(button);
}
});
but when it comes to other shapes like circles, or just someone smothering the page, how would you go about detecting that ?
one thought I had was using the edited layer, making it hidden, and detecting a pixel color of say blue, from here but that limits the color use of the photo and im not entirely sure how to implement it. any other ideas ?
EDIT:
I figured out circles after some tinkering, using Pythagoras theorem to see if mouse coordinates are smaller than the radius, but this assumes circle center of 0,0, so then offset mouse by circles actual center. example
function checkIfInsideButtonCoordinates(buttonObj, mouseX, mouseY) {
actualX = mouseX - buttonObj.x
actualY = mouseY - buttonObj.y
mousesqX = actualX * actualX
mousesqY = actualY * actualY
sqR = buttonObj.r * buttonObj.r
sqC = mousesqX + mousesqY
if (sqC < sqR) return true;
else return false;
}
Here’s how to test whether user#2 is inside user#1’s paintings
Create a second canvas used to hit-test whether user#2 is inside of user#1’s paintings.
The hit-test canvas is the same size as the drawing canvas, but it only contains user#1’s paintings…not the image.
When user#1 is painting, also draw their paintings on the hit canvas.
When user#1 is done painting, save all their paintings from the hit canvas.
You have at least 2 ways to save user#1’s paintings from the hit canvas:
Serialize all the canvas commands needed to recreate the shapes/paths that user#1 paints.
Save the hit canvas as an image using canvas.toDataURL.
When user#2 clicks, check if the corresponding pixel on the hit canvas is filled or is transparent (alpha>0).
// getImageData for the hit-test canvas (this canvas just contains user#1's paintings)
imageDataData=hitCtx.getImageData(0,0,hit.width,hit.height).data;
// look at the pixel under user#2's mouse
// return true if that pixel is filled (not transparent)
function isHit(x,y){
var pixPos=(x+y*hitWidth)*4+3;
return( imageDataData[pixPos]>10)
}
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/etA5a/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; padding:15px; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var hit=document.getElementById("hit");
var hitCtx=hit.getContext("2d");
var user2=document.getElementById("user2");
var ctx2=user2.getContext("2d");
var canvasOffset=$("#user2").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var imageDataData;
var hitWidth=hit.width;
var img=document.createElement("img");
img.onload=function(){
// left canvas: image+user#1 paintings
ctx.globalAlpha=.25;
ctx.drawImage(img,0,0);
ctx.globalAlpha=1.00;
scribble(ctx,"black");
// mid canvas: just user#1 paintings (used for hittests)
scribble(hitCtx,"black");
// right canvas: user#2
ctx2.drawImage(img,0,0);
imageDataData=hitCtx.getImageData(0,0,hit.width,hit.height).data;
}
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/colorhouse.png";
function scribble(context,color){
context.beginPath();
context.moveTo(70,2);
context.lineTo(139,41);
context.lineTo(70,41);
context.closePath();
context.rect(39,54,22,30);
context.arc(73,115,3,0,Math.PI*2,false);
context.fillStyle=color;
context.fill();
}
function handleMouseMove(e){
var mouseX=parseInt(e.clientX-offsetX);
var mouseY=parseInt(e.clientY-offsetY);
// If user#2 has a hit on user#1's painting, mid-canvas turns red
var color="black";
if(isHit(mouseX,mouseY)){ color="red"; }
scribble(hitCtx,color);
}
function isHit(x,y){
var pixPos=(x+y*hitWidth)*4+3;
return( imageDataData[pixPos]>10)
}
$("#user2").mousemove(function(e){handleMouseMove(e);});
}); // end $(function(){});
</script>
</head>
<body>
<p>Left: original image with user#1 painting</p>
<p>Mid: user#1 painting only (used for hit-testing)</p>
<p>Right: user#2 (move mouse over hit areas)</p>
<canvas id="canvas" width=140 height=140></canvas>
<canvas id="hit" width=140 height=140></canvas>
<canvas id="user2" width=140 height=140></canvas><br>
</body>
</html>
Please take a look at this little example. The clickhandler only works if you click in the middle of the line. It seems that the method isPointInPath does not consider the width of the line. Is there a way to solve this problem?
Yes, you are correct.
The new isPointInPath() works only on the centerline of a "fat" line--not the full width of the line.
It's more user friendly on closed shapes that are more than 1 pixel wide ;)
A Workaround for your exact question: Instead of drawing a fat line, draw a 20px wide rectangle.
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/QyWDY/
This code uses basic trigonometry to create a rectangle around a line. In the mousedown event handler, it redraws the rectangle transparently and then tests isPointInPath().
If you need to test a poly-line, you can use these same principles to make rectangle-lines for each segment of your poly-line.
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
// get canvas's relative position
var canvasOffset=$("#canvas").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
// line specifications
var x1=50;
var y1=50;
var x2=300;
var y2=100;
// draw the lineRectangle
var lineRect=defineLineAsRect(x1,y1,x2,y2,20);
drawLineAsRect(lineRect,"black");
// overlay the line (just as visual proof)
drawLine(x1,y1,x2,y2,3,"red");
function drawLine(x1,y1,x2,y2,lineWidth,color){
ctx.fillStyle=color;
ctx.strokeStyle=color;
ctx.lineWidth=lineWidth;
ctx.save();
ctx.beginPath();
ctx.moveTo(x1,y1);
ctx.lineTo(x2,y2);
ctx.stroke();
ctx.restore();
}
function drawLineAsRect(lineAsRect,color){
var r=lineAsRect;
ctx.save();
ctx.beginPath();
ctx.translate(r.translateX,r.translateY);
ctx.rotate(r.rotation);
ctx.rect(r.rectX,r.rectY,r.rectWidth,r.rectHeight);
ctx.translate(-r.translateX,-r.translateY);
ctx.rotate(-r.rotation);
ctx.fillStyle=color;
ctx.strokeStyle=color;
ctx.fill();
ctx.stroke();
ctx.restore();
}
function defineLineAsRect(x1,y1,x2,y2,lineWidth){
var dx=x2-x1; // deltaX used in length and angle calculations
var dy=y2-y1; // deltaY used in length and angle calculations
var lineLength= Math.sqrt(dx*dx+dy*dy);
var lineRadianAngle=Math.atan2(dy,dx);
return({
translateX:x1,
translateY:y1,
rotation:lineRadianAngle,
rectX:0,
rectY:-lineWidth/2,
rectWidth:lineLength,
rectHeight:lineWidth
});
}
function handleMouseDown(e){
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
// draw our lineRect
drawLineAsRect(lineRect,"transparent");
// test if hit in the lineRect
if(ctx.isPointInPath(mouseX,mouseY)){
alert('Yes');
}
}
canvas.addEventListener("mousedown", handleMouseDown, false);
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=310 height=115></canvas>
</body>
</html>
My question is regarding this shadowBlur feature used on the 2nd (outer) rectangle below. The shadowBlur feature is applied to every shape after this rectangle. (If you comment out the shadowColor and shadowBlur lines 21 & 22, and then uncomment the shadowColor and shadowBlur lines on lines 14 & 15, you should see what I mean.) My question is, how do I apply shadowBlur to one specific portion of the Canvas drawing without applying the feature to every succeeding portion of the Canvas. In this example I have tried creating separate variable for each canvas and context, but the problem still persists.
Attribution: These examples are based on examples from html5canvastutorials.com
<!DOCTYPE html>
<html lang="en"
<head>
<script type="text/javascript">
function addRect(){
var canvas1=document.getElementById("myCanvas");
var ctx=canvas1.getContext("2d");
var canvas3=document.getElementById("myCanvas");
var ctx3=canvas3.getContext("2d");
ctx.rect(60,60,180,80);
ctx.fillStyle="green";
//ctx.shadowColor="black";
//ctx.shadowBlur = 10;
ctx.fill();
ctx3.lineWidth = 3;
ctx3.strokeStyle='red';
ctx3.shadowColor="black";
ctx3.shadowBlur = 10;
ctx3.strokeRect(45,45,210,110);
}
function addOval(){
var canvas2=document.getElementById("myCanvas");
var context=canvas2.getContext("2d");
// define center of oval
var centerX = 288;
var centerY = 250;
// define size of oval
var height = 100;
var width = 250;
var controlRectWidth = width * 1.33;
context.beginPath();
context.moveTo(centerX,centerY - height/2);
// draw left side of oval
context.bezierCurveTo(centerX-controlRectWidth/2,centerY-height/2,
centerX-controlRectWidth/2,centerY+height/2,
centerX,centerY+height/2);
// draw right side of oval
context.bezierCurveTo(centerX+controlRectWidth/2,centerY+height/2,
centerX+controlRectWidth/2,centerY-height/2,
centerX,centerY-height/2);
context.fillStyle="red";
context.fill();
context.lineWidth=5;
context.strokeStyle="blue";
context.stroke();
context.closePath();
}
</script>
</head>
<body onload="addRect(); addOval();">
<canvas id="myCanvas" width="700" height="400">
Your browser does not support the canvas element.
</canvas>
</body>
</html>
Use either this:
ctx.save();
ctx.shadowColor="black";
ctx.shadowBlur = 10;
ctx.strokeRect(45,45,210,110);
ctx.restore();
Or this:
ctx.shadowColor="black";
ctx.shadowBlur = 10;
ctx.strokeRect(45,45,210,110);
ctx.shadowColor= undefined;
ctx.shadowBlur = undefined;
I am not sure about 'undefined' in second case - something to nullify/reset the value.
var canvas3=document.getElementById("myCanvas");
var ctx3=canvas1.getContext("2d");
change canvas1 to canvas3 in the second line. Your ctx3 is actually pointing to canvas1 which i think is wrong.
You can also consider setting the shadow color to "transparent" instead of undefined or null. This also seems to do the trick.