created a circle context and added the pattern image to fill in that circle.how can i make that pattern image grayscaled.
Is there any idea that would help me.
code :
ctx.beginPath();
var bg = new Image();
bg.src = image;
bg = function() {
var pattern = ctx.createPattern(this, "no-repeat");
ctx.fillStyle = pattern;
};
ctx.moveTo(canvasCenterHoriz, canvasCenterVert);
ctx.arc(x, y, radius, startAngle, endAngle, direction);
ctx.lineWidth = 0;
ctx.fill();
This might not be the best way to do this, but it's pretty simple and it works.
I have attached a working example below. Here's how it works:
The pattern image is drawn in an invisible canvas. Once the image has loaded, it is drawn on the canvas with a white overlay and saturation set as the global composite operation. The canvas will now contain a grayscale version of your pattern.
The temporary canvas is then converted to an image, with its source set to the canvas data url. Maybe there's a better way to send image data between two canvases, but I haven't found one.
Once the pattern is finished, your original arc is drawn with the new pattern.
let canvas = document.getElementById('grayscale-canvas');
let ctx = canvas.getContext('2d');
function makeGrayscaleBackground(image, onready) {
var bg = new Image();
bg.src = image;
bg.onload = function() {
// Create a canvas that's not attached to the DOM
var canvas = document.createElement('canvas');
canvas.setAttribute('width', this.width);
canvas.setAttribute('height', this.height);
document.body.appendChild(canvas);
let ctx = canvas.getContext('2d');
// Draw the background image
ctx.drawImage(this, 0, 0);
// Then draw a white layer on top, with the saturation composite operation
// which will remove the color from the underlying image
ctx.globalCompositeOperation = "saturation";
ctx.fillStyle = "#FFF";
ctx.fillRect(0, 0, this.width, this.height);
onready(canvas);
};
}
function drawWithImage(image) {
makeGrayscaleBackground(image, function(patternImage) {
// Green background
ctx.fillStyle = "#3f9";
ctx.fillRect(0, 0, canvas.width, canvas.height);
// Make a repeating pattern with image we created
var pattern = ctx.createPattern(patternImage, "repeat");
// Make an arc with the pattern
let x = y = canvas.width/2;
ctx.fillStyle = pattern;
ctx.beginPath();
ctx.arc(x, y, canvas.width/2-10, 0, 2*Math.PI);
ctx.fill();
})
}
// Example pattern image
// For security reasons, the image needs to be hosted on the same server as the script!
var bgImage = "data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7";
drawWithImage(bgImage);
document.getElementById('bg').src = bgImage;
<canvas width="150" height="150" id="grayscale-canvas"></canvas><br>
Actual background image: <img id="bg"><br>
Modified background image:
Related
I am trying to make a variant of the boomshine game in javascript and everything works when I draw a circular shape with the arc function. However when i try to replace the arc function with the drawImage function to use a coin image instead of a circular shape I start having problems when I clear the canvas to delete the previous drawn circular shapes. If I don't clear the canvas before rendering the images, the images are drawn on the canvas except the old images are still on the canvas. But when i do clear the canvas before rendering the images again, nothing is drawn on the canvas.
I have included screenshots, the links are below.
This is how I clear the canvas:
var ctx = game.context;
ctx.fillStyle = "darkgray";
ctx.fillRect(0, 0, game.canvas.width, game.canvas.height);
This is how i draw the image:
function drawImageBall(x,y,radius,startAngle,color)
{
var img = document.createElement('img');
img.src = 'img/coin-icon.png';
var tmpCtx= game.context;
var ax = x-radius;
var ay = y-radius;
img.onload = function() {
tmpCtx.save();
tmpCtx.beginPath();
tmpCtx.arc(x, y, radius, 0, Math.PI * 2, true);
tmpCtx.closePath();
tmpCtx.clip();
tmpCtx.drawImage(img, ax, ay, img.width, img.height);
tmpCtx.beginPath();
tmpCtx.arc(0, 0, radius, 0, Math.PI * 2, true);
tmpCtx.clip();
tmpCtx.closePath();
tmpCtx.restore();
};
}
Clearing canvas (screenshot)
Without clearing canvas (screenshot)
Keep in mind that downloading the img will take some time.
During that downloading time, Javascript does not stop(!). Instead JS will continue executing any following code. This is causing your unexpected problems.
So download the img just once at the start of your app. That way your drawImage will be done in the order that you expect because there will be no delay while your image is downloading.
Using your code, I maked some changes, I removed the tmpTcx.clip(), look the fidlle. Tip: For performace questions you don't need load the image every time that you want write the canvas.
Poor Example: https://jsfiddle.net/wf4z0d2h/1/
function clearCanvas(){
var ctx = game.context;
ctx.fillStyle = "darkgray";
ctx.fillRect(0, 0, game.canvas.width, game.canvas.height);
}
function drawImageBall(x,y,radius,startAngle,color)
{
if(x == undefined){x = 100;}
if(y == undefined){y = 100;}
if(radius == undefined){radius = 40;}
//var img = document.createElement('img');
//img.src = 'img/coin-icon.png';
//img.src = "http://ps2.lansa.com/images/icons/normal/256/coin_256.png";
var tmpCtx= game.context;
var ax = x-radius;
var ay = y-radius;
//img.onload = function() {
tmpCtx.save();
tmpCtx.beginPath();
tmpCtx.arc(x, y, radius, 0, Math.PI * 2, true);
tmpCtx.stroke(); // Draw it
tmpCtx.closePath();
//tmpCtx.clip();
tmpCtx.drawImage(img, ax, ay, img.width, img.height);
//tmpCtx.beginPath();
//tmpCtx.arc(0, 0, radius, 0, Math.PI * 2, true);
////tmpCtx.clip();
//tmpCtx.stroke(); // Draw it
//tmpCtx.closePath();
//tmpCtx.restore();
//};
}
var img = document.createElement('img');
//img.src = 'img/coin-icon.png';
img.src = "http://ps2.lansa.com/images/icons/normal/256/coin_256.png";
//drawImageBall();
img.onload = function(){
x = 0;
y = 0;
setInterval(function(){
x = x+10;
y = y+10;
clearCanvas();
drawImageBall(x,y);
},300);
}
I am trying to make a scratch card looks like
Basically I have a gray layer to scratch and it will reveal the red image.
Now I have set up the canvas and ctx is for the gray layer, but the background is fixed.
I want to have the "12345" be a variable to embed in the background,
which means I can have different number in the background image.
Here is the function I have for the scratch card.
(addEventlistener is just used for scratching the gray layer)
function bodys(height,width){
var img = new Image();
var canvas = document.querySelector('canvas');
canvas.style.position = 'absolute';
img.addEventListener('load',function(e){
var ctx;
var w = width, h = height;
var offsetX = canvas.offsetLeft, offsetY = canvas.offsetTop;
var mousedown = false;
function layer(ctx){
ctx.fillStyle = 'gray';
ctx.fillRect(0, 0, w, h);
}
function eventDown{
...
}
canvas.width=w;
canvas.height=h;
canvas.style.backgroundImage='url('+img.src+')';//here is the background image I use
ctx=canvas.getContext('2d');
ctx.fillRect(0, 0, w, h);
layer(ctx);
ctx.globalCompositeOperation = 'destination-out';
canvas.addEventListener{
...
}
});
I am having a problem with drawing and rotating image on my canvas. Basically, my approach is to create the wheel of fortune which allows customization based on the prizes in form of array. The data in this array makes up the segment inside the wheel based on the number of indexes.
The data is very simple. It is just a simple JSON object like this
var prizes = [
{product:"Axe FX", img: "https://mdn.mozillademos.org/files/5395/backdrop.png"},
{product:"Musicman JPX", img: "https://mdn.mozillademos.org/files/5395/backdrop.png"},
{product:"Ibanez JEM777V", img: "https://mdn.mozillademos.org/files/5395/backdrop.png"}
];
This data is used to create the segments inside the wheel. So I want to place the text which is currently working like a charm for me.
When drawing the wheel, I separate into two main functions. One to draw the wheel and another to draw the segments inside the wheel.
var drawPartial = function(key, lastAngle, angle) {
var value = prizes[key].product;
ctx.save();
ctx.beginPath();
ctx.lineWidth = 6;
ctx.fillStyle = segColors[key];
ctx.moveTo(centerX, centerY);
ctx.arc(centerX, centerY, size, lastAngle, angle);
ctx.lineTo(centerX, centerY);
ctx.closePath();
ctx.stroke();
ctx.fill();
ctx.save();
ctx.translate(centerX, centerY);
ctx.rotate((lastAngle+angle) / 2);
ctx.fillStyle = "#000";
ctx.fillText(value.substr(0,20), size / 2 + 20, 0);
ctx.restore();
ctx.restore();
}
var draw = function() {
var len = prizes.length;
var currentAngle = outCurrentAngle;
var lastAngle = currentAngle;
ctx.strokeStyle = '#000000';
ctx.textBaseline = "middle";
ctx.textAlign = "center";
ctx.font = "1.4em Arial";
for(var i = 1; i <= len; i++) {
var angle = (Math.PI*2) * (i/len) + currentAngle;
drawPartial(i-1, lastAngle, angle);
lastAngle = angle;
}
ctx.beginPath();
ctx.lineWidth = 2;
ctx.fillStyle = "#fff";
ctx.moveTo(centerX, centerY);
ctx.arc(centerX, centerY, size/7, 0, Math.PI*2);
ctx.closePath();
// ctx.stroke();
ctx.fill();
ctx.beginPath();
ctx.lineWidth = 10;
ctx.arc(centerX, centerY, size, 0, Math.PI*2);
ctx.closePath();
// ctx.stroke();
}
With the code above, I just simple call the draw() function and the wheel and all segments will be created accordingly. However, I want to draw the image in each segment but I don't know to make it work. This is the modification of drawPartial() for rendering images along with text
var drawPartial = function(key, lastAngle, angle) {
var value = prizes[key].product;
var img = new Image();
img.src = prizes[key].img;
img.onload = function() {
ctx.save();
ctx.drawImage(img,centerX,centerY);
ctx.save();
ctx.translate(centerX,centerY);
ctx.rotate((lastAngle+angle) / 2);
ctx.drawImage(img,centerX,centerY);
ctx.restore();
ctx.restore();
}
ctx.save();
ctx.beginPath();
ctx.lineWidth = 6;
ctx.fillStyle = segColors[key];
ctx.moveTo(centerX, centerY);
ctx.arc(centerX, centerY, size, lastAngle, angle);
ctx.lineTo(centerX, centerY);
ctx.closePath();
ctx.stroke();
ctx.fill();
ctx.save();
ctx.translate(centerX, centerY);
ctx.rotate((lastAngle+angle) / 2);
ctx.fillStyle = "#000";
ctx.fillText(value.substr(0,20), size / 2 + 20, 0);
ctx.restore();
ctx.restore();
}
You can see that I add image and its src based on the prizes object which should be called in each iteration called by the main draw() function but it never renders any image in any segment.
What I want is. In each iteration of drawPartial(), I want the image to be placed in the segment along with the text and rotated according to the angle.
Please help...
Problem
In your img.onload function you are "double translating" your centerX & centerY.
ctx.translate(centerX,centerY) will move the canvas's [0,0] origin to [centerX,centerY].
So when you ctx.drawImage(img,centerX,centerY) to draw your image, you are really double moving.
As a result your image is really being drawn at [ centerX*2, centerY*2 ].
A additional thought: Preload your images
It's best to preload all your images. That way if an image fails to load you can take reparative action before you begin drawing your wheel.
Here is how to preload all of your images so they are available when you need to draw them onto your Wheel:
// your incoming JSON
var prizesJSON='[{"product":"Axe FX","img":"https://mdn.mozillademos.org/files/5395/backdrop.png"},{"product":"Musicman JPX","img":"https://mdn.mozillademos.org/files/5395/backdrop.png"},{"product":"Ibanez JEM777V","img":"https://mdn.mozillademos.org/files/5395/backdrop.png"}]';
// the JSON converted to a JS array of objects
var prizes=JSON.parse(prizesJSON);
// preload all images
var imageURLs=[];
var imgs=[];
var imagesOK=0;
// add prize images into the image preloader
for(var i=0;i<prizes.length;i++){
imageURLs.push(prizes[i].img);
}
startLoadingAllImages(imagesAreNowLoaded);
//
function startLoadingAllImages(callback){
for (var i=0; i<imageURLs.length; i++) {
var img = new Image();
imgs.push(img);
img.onload = function(){
imagesOK++;
if (imagesOK>=imageURLs.length ) {
callback();
}
};
img.onerror=function(){alert("image load failed");}
img.src = imageURLs[i];
}
}
//
function imagesAreNowLoaded(){
// add the img objects to your prizes array objects
for(var i=0;i<prizes.length;i++){
prizes[i].imageObject=imgs[i];
// just testing (add the img to the DOM)
document.body.appendChild(imgs[i]);
}
// All images are fully loaded
// So draw your wheel now!
}
body{ background-color: ivory; }
<h4>Testing: (1) Preload all images, (2) Add imgs to DOM</h4>
I had this laying around...
I see you already have code to draw your Wheel, but I had this code in my code archive so I offer it here just in case it has some use for you.
Here is an example of how to draw a "Wheel of Fortune" with each blade containing a prize image and text. The techniques used include:
context.translate to set the rotation point to the center of the wheel.
context.rotate to rotate each blade to its desired angle.
context.textAlign & context.textBaseline to draw centered text.
context.globalAlpha to lighten each blades color so the black text has good contrast.
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
var PI=Math.PI;
var PI2=PI*2;
var bladeCount=10;
var sweep=PI2/bladeCount;
var cx=cw/2;
var cy=ch/2;
var radius=130;
var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house32x32transparent.png";
function start(){
for(var i=0;i<bladeCount;i++){
drawBlade(img,'House'+i,cx,cy,radius,sweep*i,sweep);
}
}
function drawBlade(img,text,cx,cy,radius,angle,arcsweep){
// save the context state
ctx.save();
// rotate the canvas to this blade's angle
ctx.translate(cx,cy);
ctx.rotate(angle);
// draw the blade wedge
ctx.lineWidth=1.5;
ctx.beginPath();
ctx.moveTo(0,0);
ctx.arc(0,0,radius,0,arcsweep);
ctx.closePath();
ctx.stroke();
// fill the blade, but keep the color light
// so the black text has good contrast
ctx.fillStyle='white';
ctx.fill();
ctx.fillStyle=randomColor();
ctx.globalAlpha=0.30;
ctx.fill();
ctx.globalAlpha=1.00;
// draw the text
ctx.rotate(PI/2+sweep/2);
ctx.textAlign='center';
ctx.textBaseline='middle';
ctx.fillStyle='black';
ctx.fillText(text,0,-radius+50);
// draw the img
// (resize to 32x32 so be sure orig img is square)
ctx.drawImage(img,-16,-radius+10,32,32);
// restore the context to its original state
ctx.restore();
}
function randomColor(){
return('#'+Math.floor(Math.random()*16777215).toString(16));
}
body{ background-color: ivory; }
#canvas{border:1px solid red; margin:0 auto; }
<canvas id="canvas" width=300 height=300></canvas>
I'm trying to animate a pen filling in a variable width shape, currently working with html5 canvas. Ideally, I want to be able to have the sample below both start light and get colored in dark, as well as not appear at all and get colored in as though being drawn from nothing.
source-in doesn't seem to work, at least in firefox.
The image in question is a simple-ish SVG path, so if there's a reasonable way to generate canvas clip paths from SVG bezier paths, that would work as well.
var img = new Image();
img.src = "data:image/svg+xml;base64,...";
var xRecords = [...];
var yRecords = [...];
var canvas = document.getElementById("topCanvas");
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0);
ctx.strokeStyle = "#0000ff";
ctx.lineWidth = 90;
ctx.beginPath();
ctx.lineCap = "round";
ctx.moveTo(xRecords[0], yRecords[0]);
for(var i = 0; i < xRecords.length; i++) {
ctx.lineTo(xRecords[i], yRecords[i]);
ctx.stroke();
}
http://codepen.io/matelich/pen/gpLmOW
Generating alternate versions of the image is not a big deal if that would help. Oh and the animation is just a sample.
Update This works for the most part on Chrome and IE, but not on Firefox: http://codepen.io/matelich/pen/pJNeRq
FF doesn't like your SVG dataURL.
Option#1:
You could use a .png image instead.
Option#2:
You can create a cubic Bezier curve (like SVG's "C") in canvas using context.moveTo and context.bezierCurveTo.
Then your compositing will work fine even in FF:
var canvas = document.getElementById("topCanvas");
var ctx = canvas.getContext("2d");
var img = new Image();
img.onload=start;
img.src = 'https://dl.dropboxusercontent.com/u/139992952/multple/svg2png.png';
var xRecords = [117.6970666666671, 137.5037866666671, 139.6247579166671, 138.2627966666671, 134.75555041666712, 130.4406666666671, 126.65579291666711, 124.7385766666671, 126.0266654166671, 131.8577066666671, 155.5330366666671, 191.76562666666712, 224.94953666666714, 239.47882666666712];
var yRecords = [143.95648000000128, 200.21077333333463, 232.21213000000128, 264.735546666668, 296.24260333333467, 325.19488000000126, 350.05395666666794, 369.2814133333347, 381.33883000000134, 384.687786666668, 371.9640133333346, 346.7872000000013, 322.15182666666794, 311.05237333333463];
function start(){
canvas.width=img.width;
canvas.height=img.height;
ctx.beginPath();
ctx.rect(0, 0, 640, 640);
ctx.fillStyle = 'white';
ctx.fill();
ctx.globalCompositeOperation = "darker";
ctx.drawImage(img, 0, 0);
ctx.globalCompositeOperation = "lighter";
ctx.drawImage(img, 0, 0);
ctx.globalCompositeOperation = "xor";
ctx.drawImage(img, 0, 0);
ctx.globalCompositeOperation = "destination-over";
ctx.strokeStyle = "#0000ff";
ctx.lineWidth = 90;
ctx.beginPath();
ctx.lineCap = "round";
ctx.moveTo(xRecords[0], yRecords[0]);
var i = 0;
function drawNext()
{
i++;
console.log(i+"!");
if(i >= xRecords.length) { return; }
ctx.lineTo(xRecords[i], yRecords[i]);
ctx.stroke();
setTimeout(drawNext, 500);
}
drawNext();
}
body{ background-color: white; }
#canvas{border:1px solid red;}
<canvas id="topCanvas" width=300 height=300></canvas>
I am trying to create a hole in canvas; and loading image in canvas after.
I want this canvas to contain a hole at a top layer.
I just read about counter-clockwise canvas rules and then created hole with counter clockwise position as below-
var c = document.getElementById("canvas-front");
var ctx = c.getContext("2d");
var centerX = c.width / 2;
var centerY = c.offsetTop;
var radius = 30;
ctx.beginPath();
ctx.arc(centerX, centerY, radius, 0, 2 * Math.PI,true);//boolean true to counter-clockwise
ctx.fillStyle = 'black';
ctx.fill();
I have canvas before image in it-
After applying image in this canvas-
Canvas-
<canvas id="canvas-front" width="261" height="506"></canvas>
As you can see from both the images, I can't get this hole in canvas work.
How do I create this arc so that image doesn't overlap this.
I get this issue solved-
What I had to do-
On change of file I did empty to canvas and redrew image and then while image is being loaded
the arc is being created to counter-clockwise position-
Drawing the canvas again on image change-
var canvas = document.getElementById("canvas-front");
canvas.width = canvas.width;//blanks the canvas
var c = canvas.getContext("2d");
Creating image and giving it required src from changed input-
var img = new Image();
img.src = e.target.result;
Loading image and creating arc parallely-
img.onload = function () {
c.drawImage(img, 0, 0);
var centerX = canvas.width / 2;
var centerY = canvas.offsetTop;
var radius = 30;
c.beginPath();
c.arc(centerX, centerY, radius, 0, 2 * Math.PI, true);
c.fillStyle = 'black';
c.fill();
}