I cannot clear the cursor image (canvas.getBoundingClientRect) after the cursor moves across the canvas element! I am left with a trail of appended images on the canvas.
How can I clear the trail of appended images and still keep my customized cursor (canvas.getBoundingClientRect) visible each time the canvas is cleared?
See my code :
<script>
window.addEventListener("load", CanvasProperties, false);
//Global Variables
var canvas, context;
// Canvase Element - 2D Properties
function CanvasProperties(){
canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
window.addEventListener("mousemove", CustomCursor, false);};
// Customized Cursor for Game's Canvas
function CustomCursor(e){
var canvasRect = canvas.getBoundingClientRect();
var xPosition = e.clientX - 5 - canvasRect.left;
var yPosition = e.clientY - 5 - canvasRect.top;
var img = new Image();
img.src = "hero.png";
context.drawImage(img, xPosition, yPosition, 80, 80);};
</script>
Yeah, this one was really hard to google. The answer I like the best: https://stackoverflow.com/a/2142549/607407
function CustomCursor(e){
var canvasRect = canvas.getBoundingClientRect();
var img = new Image();
img.src = "https://crossorigin.me/https://www.gravatar.com/avatar/5a061a72feb5b6580dadd5dcbc92d3b5?s=64&d=identicon&r=PG";
var xPosition = e.clientX - 5 - canvasRect.left-img.naturalWidth/2;
var yPosition = e.clientY - 5 - canvasRect.top- img.naturalHeight/2;
context.clearRect(0, 0, canvas.width, canvas.height);
context.drawImage(img, xPosition, yPosition, 80, 80);
};
Snippet:
//Global Variables - which is wrong
var canvas, context;
// Canvase Element - 2D Properties
function CanvasProperties(){
canvas = document.getElementById("canvas");
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
context = canvas.getContext("2d");
window.addEventListener("mousemove", CustomCursor, false);
}
// Customized Cursor for Game's Canvas
function CustomCursor(e){
var canvasRect = canvas.getBoundingClientRect();
var img = new Image();
img.src = "https://crossorigin.me/https://www.gravatar.com/avatar/5a061a72feb5b6580dadd5dcbc92d3b5?s=64&d=identicon&r=PG";
var xPosition = e.clientX - 5 - canvasRect.left-img.naturalWidth/2;
var yPosition = e.clientY - 5 - canvasRect.top- img.naturalHeight/2;
context.clearRect(0, 0, canvas.width, canvas.height);
context.drawImage(img, xPosition, yPosition, 80, 80);
};
CanvasProperties();
<canvas width="300" height="300" id="canvas" />
Customized Canvas Cursor - Works! :)
<!DOCTYPE html>
<html>
<body id="body" style="background-color:gray;">
<canvas id="canvas" width="600" height="400" style="background-color:white;
display:block; margin:1 auto;"> </canvas>
<script>
window.addEventListener("load", CanvasProperties, false);
//JavaScript Variables
var canvas, context;
// Canvase Element - 2D Properties
function CanvasProperties(){
canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
window.addEventListener("mousemove", CustomCursor, false);
}
// Customized Cursor for Game's Canvas
function CustomCursor(e){
var canvasRect = canvas.getBoundingClientRect();
var img = new Image(); img.src = "hero.png";
var xPosition = e.clientX - 5 - canvasRect.left;
var yPosition = e.clientY - 5 - canvasRect.top;
context.clearRect(0, 0, canvas.width, canvas.height);
context.drawImage(img, xPosition, yPosition, 80, 80);
};
CanvasProperties();
</script>
</body>
</html>
You could just use css for this very easily, as the above stated in the comments, don't reinvent the wheel, javascript is still a lot slower than the native client the browser is running on. check out this https://davidwalsh.name/css-custom-cursor and you can use the canvas:hover to make it so it uses your custom cursor whenever the mouse is over it.
Related
I have two canvases inside a container like this:
<div class="canvasContainer">
<canvas class="drawCanvas" style="z-index: 0;"></canvas>
<canvas class="drawCanvas" height="150" width="300" style="z-index: 1;"></canvas>
</div>
The first canvas (z-index 0) contains an image and the second canvas is for drawing. Both canvas have a position absolute and the canvasContainer has a relative position, but for some reason the fillRect function on the canvas context does not work when I apply the relative postion to the canvasContainer. When I remove the relative postion the fillRect function in Javascript does work, but then my canvas is positioned absolute to the body tag. Why does the fillRect function not work inside my canvasContainer when its postion is relative?
This is how I draw on my canvas
let canvas = document.createElement('canvas');
canvas.style.zIndex = "0";
canvas.className = "drawCanvas";
let context = canvas.getContext("2d");
img.onload = function() {
context.drawImage(img, 0, 0);
}
canvasContainer.appendChild(canvas);
let canvas2 = document.createElement('canvas');
canvas2.className = "drawCanvas";
canvas2.style.zIndex = "1";
canvas2.height = canvas.height;
canvas2.width = canvas.width;
canvas2.md = false;
canvas2.addEventListener('mousedown', function(event){
this.md = true;
});
canvas2.addEventListener('mouseup', function(event){
this.md = false;
});
canvas2.addEventListener('mousemove', function(event){
let mouseX = event.clientX - this.offsetLeft;
let mouseY = event.clientY - this.offsetTop;
if(this.md){
let ctx = this.getContext('2d');
ctx.fillStyle = "blue";
ctx.fillRect(mouseX, mouseY, 4, 4);
}
}
});
imageContainer.appendChild(canvas2);
}
I would like to paint a repeating grass pattern at the bottom of a canvas. The image does repeat, but it's vertically shifted.
The pattern is based on a 192x50 image:
I've noticed that if I paint from the y-coordinates 50, 100, 150, and so on, the pattern is displayed correctly. It doesn't work at other coordinates.
The resulting canvas has a vertically shifted grass pattern:
I don't know why it gets shifted like that.
Below is my code.
HTML:
<canvas id="myCanvas" style="display: block;">
</canvas>
JavaScript:
canvas.height = window.innerHeight;
canvas.width = window.innerWidth;
// Grass Background Image
var bgReady = false;
var bgImage = new Image();
bgImage.onload = function () {
bgReady = true;
};
bgImage.src = "img/grass.png";
I do the following in a loop:
if (bgReady) {
ctx.drawImage(bgImage,0, canvas.height -50,192,50);
var ptrn = ctx.createPattern(bgImage, "repeat"); // Create a pattern with this image, and set it to repeat".
ctx.fillStyle = ptrn;
ctx.fillRect(0,canvas.height - bgImage.height,canvas.width, 50); // context.fillRect(x, y, width, height);
}
I tried to put your code in jsFiddle and it seems to work as expected:
var canvas = document.getElementById('myCanvas');
canvas.height = window.innerHeight;
canvas.width = window.innerWidth;
// Grass Background Image
var bgImage = new Image();
bgImage.onload = function () {
var ctx = canvas.getContext("2d");
ctx.drawImage(bgImage,0, canvas.height -50,192,50);
var ptrn = ctx.createPattern(bgImage, "repeat"); // Create a pattern with this image, and set it to repeat".
ctx.fillStyle = ptrn;
ctx.fillRect(0,canvas.height - bgImage.height,canvas.width, 50); // context.fillRect(x, y, width, height);
};
bgImage.src = "data:image/png;base64,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";
https://jsfiddle.net/or68kcpc/
The error must be somewhere else.
The problem is that the pattern is calculated starting from the top left corner of the canvas. If you paint starting at a canvas y-coordinate that isn't an integer multiple of the image height, the visible portion of the pattern won't start at the top of the image.
To fix this, shift the drawing context down before painting with the pattern, then paint the pattern at a location shifted up, then shift the context back up:
var shiftY = canvas.height % image.height;
context.translate(0, shiftY);
context.fillRect(0, canvas.height - image.height - shiftY,
canvas.width, image.height);
context.translate(0, -shiftY);
Run the snippet below to see a demonstration. The canvas height is 120, which means that we start painting from the y-coordinate 120 - 50 = 70, which is not a multiple of 50.
To correct for this, we shift the context down by 120 % 50 = 20 and then shift the painting location up by 20. Thus, the pattern gets painted on the shifted context at the y-coordinate (70 - 20) = 50, which is a multiple of the image height.
var canvas = document.getElementById('myCanvas'),
context = canvas.getContext('2d');
canvas.height = 120;
canvas.width = 500;
var image = new Image();
image.src = 'http://i.stack.imgur.com/2bfPb.png';
image.onload = function () {
var pattern = context.createPattern(image, "repeat");
context.fillStyle = pattern;
var shiftY = canvas.height % image.height;
context.translate(0, shiftY);
context.fillRect(0, canvas.height - image.height - shiftY,
canvas.width, image.height);
context.translate(0, -shiftY);
};
#myCanvas {
border: 1px solid #666;
}
<canvas id="myCanvas"></canvas>
Let me make one more observation. The loop in your code is inefficient and the bgReady flag is unnecessary because you can run the painting code in the image.onload function, as I have done in my snippet.
I have written simple code in java script which adds JPEG image on canvas & add line on that image with simple mousedown & mouseup event. Now i wanted to add zoom-in & zoom-out effect on that image.can anybody help me out?
my js file looks as below.
var canvas;
var context;
var width;
var height;
var finalPos = {x: 0, y: 0};
var startPos = {x: 0, y: 0};
function main() {
canvas = document.getElementById('imageCanvas');
context = canvas.getContext('2d');
loadImage();
width = canvas.width;
height = canvas.height;
var canvasOffset = $('#imageCanvas').offset();
function line(cnvs) {
cnvs.beginPath();
cnvs.moveTo(startPos.x, startPos.y);
cnvs.lineTo(finalPos.x, finalPos.y);
cnvs.stroke();
}
$('#imageCanvas').mousedown(function (e) {
context.strokeStyle = 'blue';
context.lineWidth = 5;
context.lineCap = 'round';
context.beginPath();
startPos = {x: e.pageX - canvasOffset.left, y: e.pageY - canvasOffset.top};
});
$('#imageCanvas').mouseup(function (e) {
// Replace with var that is second canvas
finalPos = {x: e.pageX - canvasOffset.left, y: e.pageY - canvasOffset.top};
line(context);
});
}
;
function loadImage() {
system_image = new Image();
system_image.src = 'img/Google_OH_406TwentySecondStreet.jpg';
system_image.onload = function () {
context.drawImage(system_image, 0, 0, width, height);
};
}
You can use scale function on mousewheel
context.scale(scaleValue, scaleValue);
You must do that before drawimage on context.
I have created the example here: [link]: http://jsfiddle.net/itsjawad/5wohz3r1/
This code works well as it shoulds:
<script type="text/javascript">
var canvas = document.createElement("canvas");
canvas.id = "myCanvas";
canvas.style.height = "640px";
canvas.style.width = "384px";
canvas.style.position = "absolute";
canvas.style.border = "1px solid black";
document.body.appendChild(canvas);
var context = canvas.getContext('2d');
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
canvas.addEventListener('mousemove', function(evt) {
var mousePos = getMousePos(canvas, evt);
var message = 'Mouse position: ' + mousePos.x + ',' + mousePos.y;
var imgd = context.getImageData(mousePos.x, mousePos.y, 1, 1);
var pix = imgd.data;
document.getElementById("listener").innerHTML = "<b><i>" + message + "<br>" + pix[3] + "</i></b>";
}, false);
</script>
<div id="listener" >
</div>
It basically writes the mouse Position to the "listener" div and the alpha of the current pixel (as long as there is no content, it's - of course - 0)
But when i add this code:
var img = new Image();
img.src = 'http://www.animefighters.de/images/armor_leatherbelly.png';
context.drawImage(img, 0, 0);
There wouldn't happen anything...
What am i doing wrong? Where is the mistake?
I want to draw some images to the canvas and, after that, get the pixel data (including mouse Position and alpha of the pixel) ...
how can i realize that?
You're trying to draw the image on the canvas before it is loaded, you need to draw it onload:
var img = new Image();
img.onload = function() {
context.drawImage(img, 0, 0);
}
img.src = 'http://www.animefighters.de/images/armor_leatherbelly.png';
I want to draw a filled (or not filled) circle in a canvas on mouseclick, but I can't get my code to work properly, I've tried pretty much everything!
This is my HTML:
<div id="images"></div>
<canvas style="margin:0;padding:0;position:relative;left:50px;top:50px;" id="imgCanvas" width="250" height="250" onclick="draw(e)"></canvas>
and my current script:
var canvas = document.getElementById("imgCanvas");
var context = canvas.getContext("2d");
function createImageOnCanvas(imageId) {
canvas.style.display = "block";
document.getElementById("images").style.overflowY = "hidden";
var img = new Image(300, 300);
img.src = document.getElementById(imageId).src;
context.drawImage(img, (0), (0)); //onload....
}
function draw(e) {
var pos = getMousePos(canvas, e);
posx = pos.x;
posy = pos.y;
context.fillStyle = "#000000";
context.arc(posx, posy, 50, 0, 2 * Math.PI);
}
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
The code works just fine if and only if I remove the "use strict";, but in this assignment I have to make a code that works even with it, which is my problem.
Here is the jsFiddle
Solved it myself.
function draw(e) {
var canvas = document.getElementById("imgCanvas");
var context = canvas.getContext("2d");
var rect = canvas.getBoundingClientRect();
var posx = e.clientX - rect.left;
var posy = e.clientY - rect.top;
context.fillStyle = "#000000";
context.beginPath();
context.arc(posx, posy, 50, 0, 2 * Math.PI);
context.fill();
}
This script works fine for me.