FabricJS prevent canvas.clipTo from clipping canvas.backgroundImage - javascript

I want to set a global clipTo in my Fabric-powered Canvas that will affect all user-added layers. I want a background image and an overlay image, which are unaffected by this clip mask.
Example:
Here's what's happening in this photo:
A canvas overlay image makes the t-shirt look naturally wrinkled. This overlay image is mostly transparent
A background image in the exact shape of the t-shirt was added, which is supposed to make the t-shirt look blue
A canvas.clipTo function was added, which clips the canvas to a rectangular shape
A user-added image (the famous Fabric pug) was added
I want the user-added image (the pug) to be limited to the rectangular area.
I do not want the background image (the blue t-shirt shape) affected by the clip area.
Is there a simple way to accomplish this? I really don't want to have to add a clipTo on every single user layer rather than one tidy global clipTo.
You can play with a JS fiddle showing the problem here.


I came here with the same need and ultimately found a solution for what I'm working on. Maybe it helps:
For SVG paths, within the clipTo function you can modify the ctx directly prior to calling render(ctx) and these changes apply outside the clipped path o. Like so:
var clipPath = new fabric.Path("M 10 10 L 100 10 L 100 100 L 10 100", {
fill: 'rgba(0,0,0,0)',
});
var backgroundColor = "rgba(0,0,0, 0.2)";
var opts = {
controlsAboveOverlay: true,
backgroundColor: 'rgb(255,255,255)',
clipTo: function (ctx) {
if (typeof backgroundColor !== 'undefined') {
ctx.fillStyle = backgroundColor;
ctx.fillRect(0, 0, 300, 150);
}
clipPath.render(ctx);
}
}
var canvas = new fabric.Canvas('c', opts);
canvas.add(new fabric.Rect({
width: 50,
height: 50,
left: 30,
top: 30,
fill: 'rgb(255,0,0)'
}));
You can of course add an image instead of a color, or whatever else you want done. The trick I've found is to put it in the clipTo function on the ctx directly.
here's a fiddle


One (sorta hacky) solution: set a CSS background image on your canvas element, as shown in https://jsfiddle.net/qpnvo3cL/
<canvas id="c" width="500" height="500"></canvas>
<style>
background: url('http://fabricjs.com/assets/jail_cell_bars.png') no-repeat;
</style>
<script>
var canvas = window._canvas = new fabric.Canvas('c');
canvas.clipTo = function(ctx) {
ctx.rect(100,100,100,100);
}
</script>


Have you tried clipping a fabric Group? You could make the whole shirt one canvas. The center graphics would be one Group which you clip to where you want it. The white t-shirt and the blue overlay would of course not be part of the clipped group.
Here's an example of clipping a group:
var rect = new fabric.Rect({width:100, height: 100, fill: 'red' });
var circle = new fabric.Circle({ radius: 100, fill: 'green' });
var group1 = new fabric.Group([ circle, rect ], { left: 100, top: 100 });
canvas.add(group1);
group1.clipTo = function(ctx) {
ctx.rect(50,50,200,200);
};
See this jsfiddle I made: https://jsfiddle.net/uvepfag5/4/


I find clip rather slow so I tend to use globalCompositeOperation to do masking.
If you really need to use clip then use it in conjunction with save and restore.
// ctx is canvas context 2d
// pug is the image to be clipped
// draw your background
ctx.save(); // save state
ctx.rect(100,100,100,100); // set the clip area
ctx.clip(); // apply the clip
ctx.drawImage(pug,x,y); // draw the clipped image
ctx.restore(); // remove the clipping
// draw the other layers.
or you can
// draw background
ctx.globalCompositeOperation = "xor"; // set up the mask
ctx.fillRect(100,100,100,100); // draw the mask, could be an image.
// Alpha will effect the amount of masking,
// not available with clip
ctx.globalCompositeOperation = "destination-over";
ctx.drawImage(pug,x,y); // draw the image that is masked
ctx.globalCompositeOperation = "source-over";
// draw the stuff that needs to be over everything.
The advantage of composite operations is you have control over the clipping at a per pixel level, including the amount of clipping via the pixel alpha value

Related

How to detect transparent area click OR if user draw in transparent area in canvas?

I'm drawing an image onto a canvas using drawImage. It's a PNG that is surrounded by transparent pixels, like this:
How can I detect a drawing move path in the transparent part of that image on the canvas? I want to detect if a user draws in a transparent part.
I am trying this tutorial and I did as showing in the tutorial.
var ctx = canvas.getContext('2d'),
img = new Image;
img.onload = draw;
img.src = "http://i.stack.imgur.com/UFBxY.png";
function draw() {
// draw original image in normal mode
ctx.drawImage(img, 10, 10);
}
<canvas id=canvas width=500 height=500></canvas>
Check it out full code on Github
Check it out live demo IonCanvas

To find out is a pixel is transparent get the pixel using ctx.getImageData and look at the alpha value.
Example
// assumes ctx is defined
// returns true if pixel is fully transparent
function isTransparent(x, y) { // x, y coordinate of pixel
return ctx.getImageData(x, y, 1, 1).data[3] === 0; // 4th byte is alpha
}

javascript loaded image is blurry (PNG)

I'm having a problem drawing sprites on canvas for a school project. My code:
treeImage = new Image();
treeImage.src = "sprites/treeSprites.png";
function rocks() { //to create the rock
this.x = 1920 * Math.random(); //random location on the width of the field
this.y = ground[Math.round(this.x/3)]; //ground is an array that stores the height of the ground
this.draw = function() {
ctx.save();
ctx.translate(this.x, this.y);
ctx.rotate(Math.tan((ground[Math.floor(this.x/3)]-ground[Math.floor(this.x/3)+1])/-3));
//^rotating based on its position on the ground^
ctx.drawImage(treeImage, 200, 50, 50, 50, -25, -50, 50, 50);
ctx.restore();
}
}
len = rockArray.length; //every frame
for (var i = 0;i<len;i++) {
rockArray[i].draw();
}
I only request 50×50px from the image. Exactly outside of the 50×50 there are black lines (which shouldn't interfere because I only request the square within the black lines) but when I draw the rock, the black outlines are visible. (For other reasons, I can't remove the black lines.)
I'm guessing the image JavaScript stores when I load the image is made blurry, and then when I request that part from the image, the lines around are visible too, as the blur "spreads" the lines into the square I request.
Is there a way I can prevent this?

Use ctx.imageSmoothingEnabled = false.
This will make the image sharp instead of smoothed (blurry).
(documentation)

If you draw a vertical line at x=5 and width = 1, the canvas actually draws the line from 4.5 to 5.5 this results in aliasing and a fuzzy line. A quick way to remedy that so it is a solid line is to offset the entire canvas by half a pixel before doing anthing else.
ctx.translate(-0.5, -0.5);
(documentation)

Fabric.js: Resize canvas and continue working

I am working with Fabric.js manipulation images uploaded by users.
Here is how the application works
The uploaded image can be moved and worked on on the entire canvas (grey area). Once finished, I only need the middle area.
One the user clicks save, currently I save the green area as an image, but I also need to resize the whole canvas to be only the green area.
I tried changing the width and height of the whole canvas and then redrawAll(), but the canvas goes bottom left and only a small portion of the working area is visible, the rest is empty gray.
Is it possible to take a snapshot of the green area and continuing working on the canvas ?
Thank you

You should do extensive use of viewportTransform.
let's make an example:
you have a canvas element of 1000x1000 and you want to work on an area of 500x500 pixels.
You set the green area using a green image or a green rect of 500x500 as background image, with top left 0,0. Then you set the viewportTransform of the fabric canvas to [1, 0, 0, 1, 250, 250] this will make your canvas translate to right bottom of that grey border.
When is time to save, you have 2 choices:
1) set a viewportTransform that lets you cover everything of the original canvas and export to dataurl
2) you create an offscreen canvas of 500x500px, you move the objects over there, without touching the new canvas zoom and pan ( viewport transform ) and export that canvas to dataUrl
The snippet has some number for examples, but you need to fully understand how to use and check also the toDataUrl options of fabricCanvas.
var butt = document.getElementById('butt');
butt.onclick = function() {
canvas.viewportTransform = [2, 0, 0, 2, 0, 0];
var img = document.getElementById('export');
img.src = canvas.toDataURL()
canvas.viewportTransform = [1, 0, 0, 1, 250, 250];
canvas.renderAll();
}
var canvas = new fabric.Canvas('c', { backgroundColor: 'grey' });
var rect = new fabric.Rect({ width: 500, height: 500, fill: 'green'})
canvas.backgroundImage = rect;
canvas.viewportTransform = [1, 0, 0, 1, 250, 250];
var exampleRect = new fabric.Rect({left: 5, top: 5, width: 100, height: 100, fill: 'red' });
canvas.add(exampleRect);
canvas.renderAll();
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.11/fabric.min.js"></script>
<img id="export" />
<button id="butt" >export</button>
<canvas id="c" width="1000" height="1000"></canvas>

Clipping mask using fabricjs

I'm currently working on web app for photo editing using FabricJS and one of features I need to implement is something like Clipping masks from Photoshop.
For example I have this assets: frame, mask and image. I need to insert image inside frame and clip it with mask. Most tricky part is in requirements:
User should be able to modify image inside frame, e.g. move, rotate, skew... Frame itself also can be moved inside canvas.
Number of layers is not limited so user can add objects under or above masked image.
Masks, frames and images is not predefined, user should be able to upload and use new assets.
My current solution is this:
Load assets
Set globalCompositeOperation of image to source-out
Set clipTo function for image.
Add assets on canvas as a group
In this solution clipTo function preserve image inside rectangular area of frame and with help of globalCompositeOperation I'm clipping image to actual mask. At first sight it works fine but if I add new layer above this newly added group it will be cutted off because of globalCompositeOperation="source-out" rule. I've created JSFiddle to show this.
So, that else could I try? I've seen some posts on StackOverflow with advices to use SVGs for clipping mask, but if I understand it correctly SVG must contain only one path. This could be a problem because of third requirement of my app.
Any advice in right direction will help, because right now I'm totally stuck with this problem.

You can do this by using ClipPath property of Img Object which you want to mask. With this, you can Mask Any Type of Object. and also you need to add some Ctx Configuration in ClipTo function of Img Object.
check this link https://jsfiddle.net/naimsajjad/8w7hye2v/8/
(function() {
var img01URL = 'http://fabricjs.com/assets/printio.png';
var img02URL = 'http://fabricjs.com/lib/pug.jpg';
var img03URL = 'http://fabricjs.com/assets/ladybug.png';
var img03URL = 'http://fabricjs.com/assets/ladybug.png';
var canvas = new fabric.Canvas('c');
canvas.backgroundColor = "red";
canvas.setHeight(500);
canvas.setWidth(500);
canvas.setZoom(1)
var circle = new fabric.Circle({radius: 40, top: 50, left: 50, fixed: true, fill: '', stroke: '1' });
canvas.add(circle);
canvas.renderAll();
fabric.Image.fromURL(img01URL, function(oImg) {
oImg.scale(.25);
oImg.left = 10;
oImg.top = 10;
oImg.clipPath = circle;
oImg.clipTo = function(ctx) {
clipObject(this,ctx)
}
canvas.add(oImg);
canvas.renderAll();
});
var bili = new fabric.Path('M85.6,606.2c-13.2,54.5-3.9,95.7,23.3,130.7c27.2,35-3.1,55.2-25.7,66.1C60.7,814,52.2,821,50.6,836.5c-1.6,15.6,19.5,76.3,29.6,86.4c10.1,10.1,32.7,31.9,47.5,54.5c14.8,22.6,34.2,7.8,34.2,7.8c14,10.9,28,0,28,0c24.9,11.7,39.7-4.7,39.7-4.7c12.4-14.8-14-30.3-14-30.3c-16.3-28.8-28.8-5.4-33.5-11.7s-8.6-7-33.5-35.8c-24.9-28.8,39.7-19.5,62.2-24.9c22.6-5.4,65.4-34.2,65.4-34.2c0,34.2,11.7,28.8,28.8,46.7c17.1,17.9,24.9,29.6,47.5,38.9c22.6,9.3,33.5,7.8,53.7,21c20.2,13.2,62.2,10.9,62.2,10.9c18.7,6.2,36.6,0,36.6,0c45.1,0,26.5-15.6,10.1-36.6c-16.3-21-49-3.1-63.8-13.2c-14.8-10.1-51.4-25.7-70-36.6c-18.7-10.9,0-30.3,0-48.2c0-17.9,14-31.9,14-31.9h72.4c0,0,56-3.9,70.8,26.5c14.8,30.3,37.3,36.6,38.1,52.9c0.8,16.3-13.2,17.9-13.2,17.9c-31.1-8.6-31.9,41.2-31.9,41.2c38.1,50.6,112-21,112-21c85.6-7.8,79.4-133.8,79.4-133.8c17.1-12.4,44.4-45.1,62.2-74.7c17.9-29.6,68.5-52.1,113.6-30.3c45.1,21.8,52.9-14.8,52.9-14.8c15.6,2.3,20.2-17.9,20.2-17.9c20.2-22.6-15.6-28-16.3-84c-0.8-56-47.5-66.1-45.1-82.5c2.3-16.3,49.8-68.5,38.1-63.8c-10.2,4.1-53,25.3-63.7,30.7c-0.4-1.4-1.1-3.4-2.5-6.6c-6.2-14-74.7,30.3-74.7,30.3s-108.5,64.2-129.6,68.9c-21,4.7-18.7-9.3-44.3-7c-25.7,2.3-38.5,4.7-154.1-44.4c-115.6-49-326,29.8-326,29.8s-168.1-267.9-28-383.4C265.8,13,78.4-83.3,32.9,168.8C-12.6,420.9,98.9,551.7,85.6,606.2z',{top: 0, left: 180, fixed: true, fill: 'white', stroke: '', scaleX: 0.2, scaleY: 0.2 });
canvas.add(bili);
canvas.renderAll();
fabric.Image.fromURL(img02URL, function(oImg) {
oImg.scale(0.5);
oImg.left = 180;
oImg.top = 0;
oImg.clipPath = bili;
oImg.clipTo = function(ctx) {
clipObject(this,ctx)
}
canvas.add(oImg);
canvas.renderAll();
});
function clipObject(thisObj,ctx)
{
if (thisObj.clipPath) {
ctx.save();
if (thisObj.clipPath.fixed) {
var retina = thisObj.canvas.getRetinaScaling();
ctx.setTransform(retina, 0, 0, retina, 0, 0);
// to handle zoom
ctx.transform.apply(ctx, thisObj.canvas.viewportTransform);
thisObj.clipPath.transform(ctx);
}
thisObj.clipPath._render(ctx);
ctx.restore();
ctx.clip();
var x = -thisObj.width / 2, y = -thisObj.height / 2, elementToDraw;
if (thisObj.isMoving === false && thisObj.resizeFilter && thisObj._needsResize()) {
thisObj._lastScaleX = thisObj.scaleX;
thisObj._lastScaleY = thisObj.scaleY;
thisObj.applyResizeFilters();
}
elementToDraw = thisObj._element;
elementToDraw && ctx.drawImage(elementToDraw,
0, 0, thisObj.width, thisObj.height,
x, y, thisObj.width, thisObj.height);
thisObj._stroke(ctx);
thisObj._renderStroke(ctx);
}
}
})();
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.6.3/fabric.min.js"></script>
<canvas id="c" width="400" height="400"></canvas>

Not sure what you want.
If you want the last image loaded (named img2), the one you send to the back to not effect the layers above do the following.
You have mask,frame,img, and img2;
Put them in the following order and with the following comp settings.
img2, source-over
img, source-over
mask, destination-out
frame, source-over
If you want something else you will have to explain it in more detail.
Personally when I provide masking to the client I give them full access to all the composite methods and allow them to work out what they need to do to achieve a desired effect. Providing a UI that allows you to change the comp setting, and layer order makes it a lot easier to sort out the sometimes confusing canvas composite rules.

I'd suggest looking at this solution.
Multiple clipping areas on Fabric.js canvas
You end up with a shape layer that is used to define the mask shape. That shape then gets applied as a clipTo to your image.
The one limitation I can think off though that you might run into is when you start to rotate various shapes. I know I have it working great with a rectangle and a circle, however ran into some issues with polygons from what I recall... This was all setup under and older version of FabricJS however, so there may have been some improvements there that I'm not experienced with.
The other issue I ran into was drop shadows didn't render correctly when passed to a NodeJS server running FabricJS.

Kineticjs clip shape by mask image

I have mask image like this
How can I hide drawn elements by this mask like in photoshop (dark areas are invisible, transparent areas are shown).
It is possible to do this in raw canvas via setting globalCompositeOperation = 'destination-over', but I want it in Kineticjs

You can do something like this:
var shape = new Kinetic.Shape({
drawFunc: function(context) {
context.beginPath();
context.rect(0, 0, image.width, image.height)
context.closePath();
context.fillStrokeShape(this);
context.setAttr('globalCompositeOperation', 'destination-out');
context.drawImage(image, 0, 0);
context.setAttr('globalCompositeOperation', 'source-over');
},
fill: '#00D2FF',
});
Demo: http://jsbin.com/nebuvi/1/edit?html,js,output

As of my knowledge you can try by using opacity: 0. for your image value. or create a rectangle overlap the rectangle over your image.

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