I have this image drawn to a HTML5 canvas:
What I want to do is apply color to just a part of it.
The part where I want to apply color is defined by the following overlay image:
So, basically, I would like to guide my coloring by the overlay. So where the overlay pixels meets the main image pixels I should apply a color on the main image. At least that's how I see it working.
Notice that the overlay matches the whole image except for the lacing.
The catch is that I would like to retain the main image texture while applying the color. You can see that it has a leather texture and a "real" feel which I want to keep.
Can you please show me some methods of achieving this or share some thoughts?
Thank you!
globalCompositeOperation is your friend here.
Basically, you draw your overlay, then you set the gCO to 'source-atop' composite mode, which will make all your future drawings to only stay where there were already opaque pixels drawn, so it is important that your overlay has transparent parts.
So then you just fill a rectangle of your desired command, and finally you draw your original image, either behind, or blended to the new shape we just created.
var ctx = canvas.getContext('2d');
var loaded = 0;
function onload(){
if(++loaded === 2){
canvas.width = this.width;
canvas.height = this.height;
ctx.font = "40px sans-serif";
draw();
}
}
var original = new Image();
var overlay = new Image();
original.onload = overlay.onload = onload;
original.src = 'https://i.stack.imgur.com/vIKpI.png';
overlay.src = 'https://i.stack.imgur.com/10Tre.png';
// list of blending modes.
// Note that destination-over is a composite mode,
// which place the new drawings behind the already-there ones
var currentMode = 0;
var modes = ['destination-over', 'lighter', 'multiply', 'screen', 'overlay', 'darken',
'lighten', 'color-dodge', 'color-burn', 'hard-light', 'soft-light',
'exclusion', 'hue', 'saturation', 'color', 'luminosity' ];
function draw(){
// switch between different Blending modes
var mode = modes[currentMode];
currentMode = (currentMode+1)%(modes.length);
// clear previous
ctx.clearRect(0,0,canvas.width, canvas.height);
// draw our overlay
ctx.drawImage(overlay, 0,0);
// this will keep new drawings only where we already have existing pixels
ctx.globalCompositeOperation = 'source-atop';
ctx.fillStyle = 'red';
ctx.fillRect(0,0,canvas.width, canvas.height);
// now choose between the list of blending modes
ctx.globalCompositeOperation = mode;
// draw our original image
ctx.drawImage(original, 0,0);
// go back to default
ctx.globalCompositeOperation = 'source-over';
// just so we can know which one is shown
ctx.fillStyle = 'black';
ctx.fillText(mode, 40,40)
// do it again
setTimeout(draw, 1000)
}
canvas{
width: 100%;
}
<canvas id="canvas"></canvas>
I want to have html5 canvas text slide in behind nothing, its an effect where text appears like coming out behind some obstacle, but the obstacle is invisible.
Here is some youtube video showing how to do it in after effect:
https://www.youtube.com/watch?v=KIYMy7vLLRo
I know how to slide a text along canvas, and one idea I got is having two canvases on top of each other, and top canvas is smaller and contains the text that is initially out of canvas and slides in. But if there is a way to do it with just one canvas that would be great.
You can using a clipping path to mask out part of the text.
Save the existing clipping path using the save() method. Create a shape/path and make it the new clipping path using the clip() method. Draw your text. Store the previous clipping path using the restore() method.
For example, suppose your canvas is 100 pixels by 100 pixels. The following will draw text on only the left side of the canvas.
context.save();
context.rect(0, 0, 50, 100);
context.clip();
context.fillText("Draw some text.", 30, 50);
context.restore();
jsFiddle : https://jsfiddle.net/CanvasCode/vgpov2yk/3
var c = document.getElementById('myCanvas');
var ctx = c.getContext("2d");
// Positions for the text startint off
var xText = -100;
var yText = 150;
// This will update the canvas as fast as possible (not good)
setInterval(function () {
// Clear the canvas
ctx.fillStyle = "#F0F";
ctx.fillRect(0, 0, c.width, c.height);
ctx.save()
// We create a clip rect
ctx.rect(200,0,400,400);
ctx.clip();
// Draw text
ctx.fillStyle = "#FFF";
ctx.font = "30px Arial";
ctx.fillText("Hello World", xText, yText);
ctx.restore();
// Increase the text x position
if (xText < 200) {
xText += 0.5;
}
}, 15);
All you have to do is use a clip rect which is like a mask in image editing.
I'm struggling to make smooth image resized in canvas in Chrome. In firefox it works well, but in Chrome I'm stuck on making it smooth.
Here is the jsfiddle
http://jsfiddle.net/flashmandv/oxtrypmy/
var AVATAR_SIZE = 100;
var WHITE_BORDER_SIZE = 3;
var stage = new createjs.Stage("canvas");
var avCont = new createjs.Container();
stage.addChild(avCont);
avCont.x = avCont.y = 20;
//add white circle
var whiteBorderCircle = new createjs.Shape();
var radius = (AVATAR_SIZE+WHITE_BORDER_SIZE*2)/2;
whiteBorderCircle.graphics.beginFill("white").drawCircle(radius, radius, radius);
avCont.addChild(whiteBorderCircle);
//add avatar image mask
var avatarMask = new createjs.Shape();
avatarMask.graphics.beginFill("red").drawCircle(AVATAR_SIZE/2+WHITE_BORDER_SIZE, AVATAR_SIZE/2+WHITE_BORDER_SIZE, AVATAR_SIZE/2);
//add avatar image
var image = new Image();
image.onload = function(){
var bitmap = new createjs.Bitmap(image);
bitmap.mask = avatarMask;
var bounds = bitmap.getBounds();
bitmap.scaleX = (AVATAR_SIZE+WHITE_BORDER_SIZE*2) / bounds.width;
bitmap.scaleY = (AVATAR_SIZE+WHITE_BORDER_SIZE*2) / bounds.height;
avCont.addChild(bitmap);
stage.update();
};
image.src = 'http://files.sharenator.com/sunflowers-s800x800-423444.jpg';
Notice the jagged image
Please help
It is due to how clipping works in Chrome. Clip masks are pretty brutal in Chrome while in Firefox you get anti-aliasing along the non-straight edges.
Here is a proof-of-concept for this (run this in Chrome and in FF to see the difference):
http://jsfiddle.net/r65fcqoy/
The only way to get around this is to use composite modes instead, which basically means you need to rewrite your code unless the library you're using support this in some way.
One use of a composite mode is to use it to fill anything inside an existing drawing on the canvas.
We'll first create the filled circle we want the image to appear inside
Change comp mode to source-in and draw image
Then we go back to normal comp mode and draw the outer border
Here is an approach using vanilla JavaScript where you can control how you plug things together - this is maybe not what you're after but there is really not much option if the library as said doesn't support comp mode instead of clipping:
var canvas = document.getElementById('canvas'),
ctx = canvas.getContext('2d'),
img = new Image,
x = 70, y =70;
var AVATAR_SIZE = 100;
var WHITE_BORDER_SIZE = 3;
var radius = (AVATAR_SIZE+WHITE_BORDER_SIZE*2)/2;
img.onload = function() {
// first draw the circle for the inner image:
ctx.arc(x, y, AVATAR_SIZE*0.5, 0 , 2*Math.PI);
ctx.fill();
// now, change composite mode:
ctx.globalCompositeOperation = 'source-in';
// draw image in top
ctx.drawImage(img, x-AVATAR_SIZE*0.5, y-AVATAR_SIZE*0.5,
AVATAR_SIZE, AVATAR_SIZE);
// change back composite mode to default:
ctx.globalCompositeOperation = 'source-over';
// now draw border
ctx.beginPath();
ctx.arc(x, y, radius + 5, 0, 2*Math.PI);
ctx.closePath();
ctx.lineWidth = 10;
ctx.strokeStyle = '#ffa94e';
ctx.stroke();
};
img.src = 'http://i.stack.imgur.com/PB8lN.jpg';
<canvas id=canvas width=500 height=180></canvas>
Another solution to this would be in onload function to add another shape above the masked image to simply cover the jagged edges of the clipping mask
I am looking to simply add a dot to the canvas.
I have the following code:
var canv = document.getElementById("myCanvas");
var context = canv.getContext("2d");
var radius = 5;
var putPoint = function(e){
context.beginPath();
context.arc(e.clientX, e.clientY, radius, 0, Math.PI*2);
context.fill();
}
canv.addEventListener('mousedown', putPoint);
I was learning how to do this with a video tutorial. However they were setting the canvas
as the full width/height of the browser window, whereas my canvas is on 400px * 400px and is contained within a div. I think this is the problem.
So my question is are the "e.client" parameters not working because of my canvas being only
a small part of the window?
If so, how can I track the mouse co-ordinates on my canvas?
You must adjust e.clientX/e.clientY by the offset of the canvas element.
Otherwise you're miscalculating the position of your mouse and your dot is probably being drawn outside the bounds of your canvas.
Here's your code modified to take the canvas offset into account.
var putPoint = function(e){
var BB=canvas.getBoundingClientRect();
var offsetX=BB.left;
var offsetY=BB.top;
var mouseX=e.clientX-BB.left;
var mouseY=e.clientY-BB.top;
context.beginPath();
context.arc(mouseX,mouseY,radius,0,Math.PI*2);
context.fill();
}
Using the HTML5 <canvas> element, I would like to load an image file (PNG, JPEG, etc.), draw it to the canvas completely transparently, and then fade it in. I have figured out how to load the image and draw it to the canvas, but I don't know how to change its opacity.
Here's the code I have so far:
var canvas = document.getElementById('myCanvas');
if (canvas.getContext)
{
var c = canvas.getContext('2d');
c.globalAlpha = 0;
var img = new Image();
img.onload = function() {
c.drawImage(img, 0, 0);
}
img.src = 'image.jpg';
}
Will somebody please point me in the right direction like a property to set or a function to call that will change the opacity?
I am also looking for an answer to this question, (to clarify, I want to be able to draw an image with user defined opacity such as how you can draw shapes with opacity) if you draw with primitive shapes you can set fill and stroke color with alpha to define the transparency. As far as I have concluded right now, this does not seem to affect image drawing.
//works with shapes but not with images
ctx.fillStyle = "rgba(255, 255, 255, 0.5)";
I have concluded that setting the globalCompositeOperation works with images.
//works with images
ctx.globalCompositeOperation = "lighter";
I wonder if there is some kind third way of setting color so that we can tint images and make them transparent easily.
EDIT:
After further digging I have concluded that you can set the transparency of an image by setting the globalAlpha parameter BEFORE you draw the image:
//works with images
ctx.globalAlpha = 0.5
If you want to achieve a fading effect over time you need some kind of loop that changes the alpha value, this is fairly easy, one way to achieve it is the setTimeout function, look that up to create a loop from which you alter the alpha over time.
Some simpler example code for using globalAlpha:
ctx.save();
ctx.globalAlpha = 0.4;
ctx.drawImage(img, x, y);
ctx.restore();
If you need img to be loaded:
var img = new Image();
img.onload = function() {
ctx.save();
ctx.globalAlpha = 0.4;
ctx.drawImage(img, x, y);
ctx.restore()
};
img.src = "http://...";
Notes:
Set the 'src' last, to guarantee that your onload handler is called on all platforms, even if the image is already in the cache.
Wrap changes to stuff like globalAlpha between a save and restore (in fact use them lots), to make sure you don't clobber settings from elsewhere, particularly when bits of drawing code are going to be called from events.
Edit: The answer marked as "correct" is not correct.
It's easy to do. Try this code, swapping out "ie.jpg" with whatever picture you have handy:
<!DOCTYPE HTML>
<html>
<head>
<script>
var canvas;
var context;
var ga = 0.0;
var timerId = 0;
function init()
{
canvas = document.getElementById("myCanvas");
context = canvas.getContext("2d");
timerId = setInterval("fadeIn()", 100);
}
function fadeIn()
{
context.clearRect(0,0, canvas.width,canvas.height);
context.globalAlpha = ga;
var ie = new Image();
ie.onload = function()
{
context.drawImage(ie, 0, 0, 100, 100);
};
ie.src = "ie.jpg";
ga = ga + 0.1;
if (ga > 1.0)
{
goingUp = false;
clearInterval(timerId);
}
}
</script>
</head>
<body onload="init()">
<canvas height="200" width="300" id="myCanvas"></canvas>
</body>
</html>
The key is the globalAlpha property.
Tested with IE 9, FF 5, Safari 5, and Chrome 12 on Win7.
This suggestion is based on pixel manipulation in canvas 2d context.
From MDN:
You can directly manipulate pixel data in canvases at the byte level
To manipulate pixels we'll use two functions here - getImageData and putImageData.
getImageData usage:
var myImageData = context.getImageData(left, top, width, height);
The putImageData syntax:
context.putImageData(myImageData, x, y);
Where context is your canvas 2d context, and x and y are the position on the canvas.
So to get red green blue and alpha values, we'll do the following:
var r = imageData.data[((x*(imageData.width*4)) + (y*4))];
var g = imageData.data[((x*(imageData.width*4)) + (y*4)) + 1];
var b = imageData.data[((x*(imageData.width*4)) + (y*4)) + 2];
var a = imageData.data[((x*(imageData.width*4)) + (y*4)) + 3];
Where x is the horizontal offset, y is the vertical offset.
The code making image half-transparent:
var canvas = document.getElementById('myCanvas');
var c = canvas.getContext('2d');
var img = new Image();
img.onload = function() {
c.drawImage(img, 0, 0);
var ImageData = c.getImageData(0,0,img.width,img.height);
for(var i=0;i<img.height;i++)
for(var j=0;j<img.width;j++)
ImageData.data[((i*(img.width*4)) + (j*4) + 3)] = 127;//opacity = 0.5 [0-255]
c.putImageData(ImageData,0,0);//put image data back
}
img.src = 'image.jpg';
You can make you own "shaders" - see full MDN article here
You can. Transparent canvas can be quickly faded by using destination-out global composite operation. It's not 100% perfect, sometimes it leaves some traces but it could be tweaked, depending what's needed (i.e. use 'source-over' and fill it with white color with alpha at 0.13, then fade to prepare the canvas).
// Fill canvas using 'destination-out' and alpha at 0.05
ctx.globalCompositeOperation = 'destination-out';
ctx.fillStyle = "rgba(255, 255, 255, 0.05)";
ctx.beginPath();
ctx.fillRect(0, 0, width, height);
ctx.fill();
// Set the default mode.
ctx.globalCompositeOperation = 'source-over';
I think this answers the question best, it actually changes the alpha value of something that has been drawn already. Maybe this wasn't part of the api when this question was asked.
Given 2d context c.
function reduceAlpha(x, y, w, h, dA) {
let screenData = c.getImageData(x, y, w, h);
for(let i = 3; i < screenData.data.length; i+=4){
screenData.data[i] -= dA; //delta-Alpha
}
c.putImageData(screenData, x, y );
}
Set global Alpha draw the object that has opacity then set back to normal.
//////////////////////// circle ///////////////////////
ctx.globalAlpha = 0.75;
ctx.beginPath();
ctx.arc(x1, y1, r1, 0, Math.PI*2);
ctx.fillStyle = colour;
ctx.fill();
ctx.closePath();
ctx.globalAlpha = 1;
How i made it..on canvas i first draw rect in a selfrun function 0,0,canvas.width,canvas.height as a background of canvas and i set globalAlpha to 1 .then i draw other shapes in ather own functions and set their globalAlpha to 0.whatever number they dont affect each other even images.
Like Ian said, use c.globalAlpha = 0.5 to set the opacity, type up the rest of the settings for the square, then follow up with c.save();. This will save the settings for the square then you can c.rect and c.fillStyle the square how you want it. I chose not to wrap it with c.restore afterwards and it worked well
If you use jCanvas library you can use opacity property when drawing. If you need fade effect on top of that, simply redraw with different values.
You can't. It's immediate mode graphics. But you can sort of simulate it by drawing a rectangle over it in the background color with an opacity.
If the image is over something other than a constant color, then it gets quite a bit trickier. You should be able to use the pixel manipulation methods in this case. Just save the area before drawing the image, and then blend that back on top with an opacity afterwards.