programatically add images to canvas in fabricJS - fabricjs

I have an image to be added to a fabricJS canvas. The user will specify the number on times the same image should be added on the canvas.
When I loop through the number of times the user entered and use fabric.Image.fromURL to add, it gets added just once and only to the last location.
EDIT:
Here is the jsfiddle on what I am trying to do
http://jsfiddle.net/apsixion/9g0Lfydw/3/

Here is how I solved it today..
Moved the code to draw the image to a different function outside and called the function in a look. May not be the most optimal solution, but works for me.
// create a wrapper around native canvas element (with id="c")
var canvas = new fabric.Canvas('c', {
selection: false
});
function drawRectangles(number) {
i = 0;
var pic =
"http://depts.washington.edu/hplab/wordpress/wp-content/uploads/2014/10/smiley-e1415084033498.jpeg";
for (var i = 0; i < number; i++) {
var rect = new fabric.Rect({
left: 5 + i * 160,
top: 10,
width: 150,
height: 150,
lockRotation: true,
lockMovementX: false,
lockMovementY: false
});
canvas.add(rect);
}
for (var k = 0; k < number; k++) {
drawStars(k);
}
}
function drawStars(k) {
var picStars =
"http://reviews.babymonitorsdirect.co.uk/images/5-stars.jpg";
fabric.Image.fromURL(picStars, function (img2) {
img2.set({
lockRotation: true,
lockMovementX: true,
lockMovementY: true,
left: 5 + k * 160,
top: 10,
width: 50,
height: 50,
lockScalingX: true,
lockScalingY: true,
selectable: true,
hasControls: false
});
canvas.add(img2);
});
}
drawRectangles(5);
http://jsfiddle.net/apsixion/z6dq0dp9/2/

Related

Fabricjs - selection only via border

I'm using Fabric.js to draw some rectangles on a canvas. The default behavior is that clicking inside a rectangle selects it. How can I change the behavior such that it is only selected when clicking on the border of the rectangle?
Clicking inside the rectangle but not on the border should do nothing.
You can see this behavior by drawing a rectangle on a TradingView.com chart
It there an option for this in fabric, and if not how could I go around implementing it?
This approach overrides the _checkTarget method within FabricJS to reject clicks that are more than a specified distance from the border (defined by the clickableMargin variable).
//sets the width of clickable area
var clickableMargin = 15;
var canvas = new fabric.Canvas("canvas");
canvas.add(new fabric.Rect({
width: 150,
height: 150,
left: 25,
top: 25,
fill: 'green',
strokeWidth: 0
}));
//overrides the _checkTarget method to add check if point is close to the border
fabric.Canvas.prototype._checkTarget = function(pointer, obj, globalPointer) {
if (obj &&
obj.visible &&
obj.evented &&
this.containsPoint(null, obj, pointer)){
if ((this.perPixelTargetFind || obj.perPixelTargetFind) && !obj.isEditing) {
var isTransparent = this.isTargetTransparent(obj, globalPointer.x, globalPointer.y);
if (!isTransparent) {
return true;
}
}
else {
var isInsideBorder = this.isInsideBorder(obj);
if(!isInsideBorder) {
return true;
}
}
}
}
fabric.Canvas.prototype.isInsideBorder = function(target) {
var pointerCoords = target.getLocalPointer();
if(pointerCoords.x > clickableMargin &&
pointerCoords.x < target.getScaledWidth() - clickableMargin &&
pointerCoords.y > clickableMargin &&
pointerCoords.y < target.getScaledHeight() - clickableMargin) {
return true;
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.6.2/fabric.min.js"></script>
<canvas id="canvas" height="300" width="400"></canvas>
Fabric.js uses Object.containsPoint() to determine whether a mouse event should target the object. This method, in turn, calculates the object's edges via Object._getImageLines() and checks how many times the projection of a mouse pointer crossed those lines.
The solution below calculates additional inner edges based on the coordinates of each corner, therefore object scale and rotation are taken care of automatically.
const canvas = new fabric.Canvas('c', {
enableRetinaScaling: true
})
const rect = new fabric.Rect({
left: 0,
top: 0,
width: 100,
height: 100,
dragBorderWidth: 15, // this is the custom attribute we've introduced
})
function innerCornerPoint(start, end, offset) {
// vector length
const l = start.distanceFrom(end)
// unit vector
const uv = new fabric.Point((end.x - start.x) / l, (end.y - start.y) / l)
// point on the vector at a given offset but no further than side length
const p = start.add(uv.multiply(Math.min(offset, l)))
// rotate point
return fabric.util.rotatePoint(p, start, fabric.util.degreesToRadians(45))
}
rect._getInnerBorderLines = function(c) {
// the actual offset from outer corner is the length of a hypotenuse of a right triangle with border widths as 2 sides
const offset = Math.sqrt(2 * (this.dragBorderWidth ** 2))
// find 4 inner corners as offsets rotated 45 degrees CW
const newCoords = {
tl: innerCornerPoint(c.tl, c.tr, offset),
tr: innerCornerPoint(c.tr, c.br, offset),
br: innerCornerPoint(c.br, c.bl, offset),
bl: innerCornerPoint(c.bl, c.tl, offset),
}
return this._getImageLines(newCoords)
}
rect.containsPoint = function(point, lines, absolute, calculate) {
const coords = calculate ? this.calcCoords(absolute) : absolute ? this.aCoords : this.oCoords
lines = lines || this._getImageLines(coords)
const innerRectPoints = this._findCrossPoints(point, lines);
const innerBorderPoints = this._findCrossPoints(point, this._getInnerBorderLines(coords))
// calculate intersections
return innerRectPoints === 1 && innerBorderPoints !== 1
}
canvas.add(rect)
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.6.2/fabric.min.js"></script>
<canvas id="c" width="400" height="300"></canvas>
here is my approach, when rect is clicked I am calculating where it is clicked and
if it is not clicked on border I have to set canvas.discardActiveObject , see comments on code
var canvas = new fabric.Canvas('c', {
selection: false
});
var rect = new fabric.Rect({
left: 50,
top: 50,
width: 100,
height: 100,
strokeWidth: 10,
stroke: 'red',
selectable: false,
evented: true,
hasBorders: true,
lockMovementY: true,
lockMovementX: true
})
canvas.on("mouse:move", function(e) {
if (!e.target || e.target.type != 'rect') return;
// when selected event is fired get the click position.
var pointer = canvas.getPointer(e.e);
// calculate the click distance from object to be exact
var distanceX = pointer.x - rect.left;
var distanceY = pointer.y - rect.top;
// check if click distanceX/Y are less than 10 (strokeWidth) or greater than 90 ( rect width = 100)
if ((distanceX <= rect.strokeWidth || distanceX >= (rect.width - rect.strokeWidth)) || (distanceY <= rect.strokeWidth || distanceY >= (rect.height - rect.strokeWidth))) {
rect.set({
hoverCursor: 'move',
selectable: true,
lockMovementY: false,
lockMovementX: false
});
document.getElementById('result').innerHTML = 'on border';
} else {
canvas.discardActiveObject();
document.getElementById('result').innerHTML = 'not on border';
rect.set({
hoverCursor: 'default',
selectable: false,
lockMovementY: true,
lockMovementX: true
});
}
});
canvas.add(rect);
canvas.renderAll();
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.6.2/fabric.min.js"></script>
<div id="result" style="width: 100%; "></div>
<canvas id="c" width="600" height="200"></canvas>
<pre>
</pre>
ps: you can also set the rect property to selectable: false and call canvas.setActiveObject(this); to make it selection inside if statement.

Fabricjs mask object with transformation

I'm trying to mask an object using Fabric.js free drawing brush. It works fine if the object is in its default position and without any transformations. But once I add transformations to the object, the mask is placed in the wrong position. I'm not sure how to solve this. Can someone take a look?
I want to be able to apply any transformations, before or after the mask, without messing up the mask.
let canvas = new fabric.Canvas("canvas", {
backgroundColor: "lightgray",
width: 1280,
height: 720,
preserveObjectStacking: true,
selection: false,
stateful: true
});
canvas.isDrawingMode = true;
canvas.freeDrawingBrush.color = "black";
canvas.freeDrawingBrush.width = 2;
canvas.on("path:created", function(options) {
clip(options.path);
});
function clip(path) {
canvas.isDrawingMode = false;
canvas.remove(path);
let mask = new fabric.Path(path.path, {
top: object.top,
left: object.left,
objectCaching: false,
strokeWidth: 0,
pathOffset: {
x: 0,
y: 0
}
});
let originalObjLeft = object.left,
originalObjTop = object.top;
object.set({
clipTo: function(ctx) {
mask.set({
left: -object.width / 2 - mask.width / 2 - originalObjLeft,
top: -object.height / 2 - mask.height / 2 - originalObjTop,
objectCaching: false
});
mask.render(ctx);
}
});
canvas.requestRenderAll();
}
// image
let image = new Image();
let object;
image.onload = function() {
object = new fabric.Image(image, {
width: 500,
height: 500,
//scaleX: 0.8,
//scaleY: 0.8,
//angle: 45,
top: 50,
left: 300
});
canvas.add(object);
};
image.src = "http://i.imgur.com/8rmMZI3.jpg";
I implement an exemple with some transformations (scaleX,scaleY,left,top).
I'm strugle to find a solution when the inital object have an angle different than 0. For the current solution I need it to divide the maskscale with the object scale and also adjust the positions.
let canvas = new fabric.Canvas("canvas", {
backgroundColor: "lightgray",
width: 1280,
height: 720,
preserveObjectStacking: true,
selection: false,
stateful: true
});
canvas.isDrawingMode = true;
canvas.freeDrawingBrush.color = "black";
canvas.freeDrawingBrush.width = 2;
canvas.on("path:created", function(options) {
clip(options.path);
});
function clip(path) {
canvas.isDrawingMode = false;
canvas.remove(path);
let mask = new fabric.Path(path.path, {
top: object.top,
left: object.left,
objectCaching: false,
strokeWidth: 0,
scaleX : 1/object.scaleX,
scaleY : 1/object.scaleY,
pathOffset: {
x: 0,
y: 0
}
});
let originalObjLeft = object.left,
originalObjTop = object.top,
originalMaskScaleX = mask.scaleX,
originalMaskScaleY = mask.scaleY,
originalObjScaleX = object.scaleX,
originalObjScaleY = object.scaleY;
object.set({
clipTo: function(ctx) {
mask.set({
left: -object.width / 2 -( mask.width / 2 * originalMaskScaleX) - originalObjLeft/originalObjScaleX ,
top: -object.height / 2 -( mask.height / 2 * originalMaskScaleY) - originalObjTop/originalObjScaleY ,
objectCaching: false
});
mask.render(ctx);
}
});
canvas.requestRenderAll();
}
// image
let image = new Image();
image.onload = function() {
object = new fabric.Image(image, {
width: 500,
height: 500,
scaleX: 0.8,
scaleY: 0.8,
// angle: 45,
top: 50,
left: 100
});
canvas.add(object);
};
image.src = "http://i.imgur.com/8rmMZI3.jpg";
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.3.6/fabric.js"></script>
<div class="canvas__wrapper">
<canvas id="canvas" width="1280" height="720"></canvas>
</div>
You can check here for loadFromJSON support.
The only problem remains is when the object is rotated.
Basically whenever you set an angle, your context matrix has been transformed. In order to mask properly you need to return to initial state of the Transformation Matrices. Fabricjs handles first matrix with center point of an object (calculates center of an object with or without an angle). Second matrix is rotating matrix, and third - scaling.
To display image with all options which are set to an object, you need to multiply all Matrices:
(First Matrix * Second Matrix) * Third Matrix
So the idea of clipping will be reverse engineering of rotating context and multiplications of matrices:
difference between center points of regular object without rotation and center point of the same object but with rotation. After that take result of subtractions and divide by original object scale value.
let canvas = new fabric.Canvas("canvas", {
backgroundColor: "lightgray",
width: 1280,
height: 720,
preserveObjectStacking: true,
selection: false,
stateful: true
});
const angle = 45;
let objectHasBeenRotated = false;
canvas.isDrawingMode = true;
canvas.freeDrawingBrush.color = "black";
canvas.freeDrawingBrush.width = 2;
canvas.on("path:created", function (options) {
clip(options.path);
});
function clip(path) {
canvas.isDrawingMode = false;
canvas.remove(path);
let mask = new fabric.Path(path.path, {
top: 0,
left: 0,
objectCaching: false,
strokeWidth: 0,
scaleX: 1 / object.scaleX,
scaleY: 1 / object.scaleY,
pathOffset: {
x: 0,
y: 0,
}
});
let originalObjLeft = object.left,
originalObjTop = object.top,
originalMaskScaleX = mask.scaleX,
originalMaskScaleY = mask.scaleY,
originalObjScaleX = object.scaleX,
originalObjScaleY = object.scaleY,
transformedTranslate = object.translateToGivenOrigin({
x: object.left,
y: object.top
}, object.originX, object.originY, 'center', 'center'),
originalTransformLeft = transformedTranslate.x - object.getCenterPoint().x,
originalTransformTop = transformedTranslate.y - object.getCenterPoint().y;
object.set({
clipTo: function (ctx) {
ctx.save();
ctx.rotate(-angle * Math.PI / 180);
ctx.translate(originalTransformLeft / originalObjScaleX, originalTransformTop / originalObjScaleY)
mask.set({
left: -object.width / 2 - (mask.width / 2 * originalMaskScaleX) - originalObjLeft / originalObjScaleX,
top: -object.height / 2 - (mask.height / 2 * originalMaskScaleY) - originalObjTop / originalObjScaleY,
objectCaching: false
});
mask.render(ctx);
ctx.restore();
}
});
canvas.requestRenderAll();
}
// image
let image = new Image();
image.onload = function () {
object = new fabric.Image(image, {
width: 500,
height: 500,
scaleX: 0.8,
scaleY: 0.8,
angle: angle,
top: 50,
left: 300,
id: 'pug'
});
canvas.add(object);
};
image.src = "http://i.imgur.com/8rmMZI3.jpg";
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.3.6/fabric.js"></script>
<div class="canvas__wrapper">
<canvas id="canvas" width="1280" height="720"></canvas>
</div>

fabric.js rotate object around canvas center smoothly

I try to rotate an object around the canvas center smoothly using a slider,
I use fabric.util.rotatePoint to find the new center point and set the new angle,but it seems not exactly around the center point and the object position is jumping.
https://jsfiddle.net/j0g1tLsb/26/
here is my code doing this:
const canvas = new fabric.Canvas('c', { width: innerWidth, height: innerHeight });
canvas.controlsAboveOverlay = true;
canvas.preserveObjectStacking = true;
const rect = new fabric.Rect({
width: 300,
height: 150,
left: 400,
top: 400,
fill: "lightgray",
originX: 'center',
originY: 'center'
});
const centerPoint = new fabric.Circle({
originX: 'center',
originY: 'center',
top: innerHeight/2,
left: innerWidth/2,
radius: 10,
fill: 'red',
hasControls: false,
selectable:false
});
const log = new fabric.Text('', {
left: 30,
top: 30,
originX: 'left',
originY: 'top',
fontSize: 18,
evented: false,
selectable: false
});
canvas.add(rect, centerPoint, log);
document.getElementById('img-rotation').oninput = function() {
rect.set('angle', this.value);
var posNewCenter = fabric.util.rotatePoint(
rect.getCenterPoint(),
canvas.getVpCenter(),
fabric.util.degreesToRadians(this.value)
);
rect.set({
left: posNewCenter.x,
top: posNewCenter.y,
angle: this.value
});
log.set('text', `angle: ${Math.round(rect.angle)} \nleft: ${rect.left} \ntop: ${rect.top}`);
canvas.requestRenderAll();
};
rect.on('modified', () => {
log.set('text', `angle: ${Math.round(rect.angle)} \nleft: ${rect.left} \ntop: ${rect.top}`);
canvas.renderAll();
});
Your problem is in getting center point from the rectangle every time. You need just set new Point from the original rectangle position.
var posNewCenter = fabric.util.rotatePoint(
new fabric.Point(400, 400), //here is your mistake
canvas.getVpCenter(),
fabric.util.degreesToRadians(this.value)
);
rect.set({
left: posNewCenter.x,
top: posNewCenter.y,
angle: this.value
});
Working fiddle
UPDATE:
In order of the modification of the Rectangle you need to use object:modified event to reassign top and left coordinates.
First of all declare top and left variables and use them inside rectangle object:
let top = 400;
let left = 400;
const rect = new fabric.Rect({
...
left: left,
top: top,
...
targetObj: 'rectangle' //you can use any value or ID, it's only for targeting purpose
});
Then you need to check when object is modified. If event is fired then check if it is rectangle.
canvas.on('object:modified', (e) => {
if (e.target.hasOwnProperty('targetObj') && e.target.targetObj === 'rectangle') {
left = e.target.get('left');
top = e.target.get('top');
}
})
Finally, use left and top variables inside oninput event of the slider:
var posNewCenter = fabric.util.rotatePoint(
new fabric.Point(left, top),
canvas.getVpCenter(),
fabric.util.degreesToRadians(this.value)
);
Working updated fiddle

How to align object by bounding box in FabricJS?

Wondering if there is a way to align objects in FabricJs by their bounding box?
I'm using obj.getBoundingRect() function to determine objects bounders, then compare them with a bounding box (BB) coordinates of an Active one (that one which I move). If I see that something falls between some gap (let's say 10px) I assign an active object top to be the same top as a comparable element by using a .setTop() property.
The problem is that TOP is not a right attribute to use, since the top of the bounding box may differ between elements. For example, 2 elements with the same top but different angle will have different Bounding Box Top...
Hope you see my point...
https://jsfiddle.net/redlive/hwcu1p4f/
var canvas = this.__canvas = new fabric.Canvas('canvas');
//fabric.Object.prototype.transparentCorners = false;
var red = new fabric.Rect({
id: 1,
left: 100,
top: 50,
width: 100,
height: 100,
fill: 'red',
angle: 0,
padding: 10
});
canvas.add(red);
var green = new fabric.Rect({
id: 2,
left: 250,
top: 180,
width: 100,
height: 100,
fill: 'green',
angle: 45,
padding: 10
});
canvas.add(green);
canvas.renderAll();
canvas.on("object:moving", function(e){
const draggableObj = e.target;
const draggableObjBound = draggableObj.getBoundingRect();
canvas.forEachObject(function(obj) {
if (obj.id !== draggableObj.id) {
var bound = obj.getBoundingRect();
if (draggableObjBound.top > bound.top - 10 && draggableObjBound.top < bound.top + 10) {
draggableObj.setTop(obj.getTop());
}
}
});
});
canvas.forEachObject(function(obj) {
var setCoords = obj.setCoords.bind(obj);
obj.on({
moving: setCoords,
scaling: setCoords,
rotating: setCoords
});
});
canvas.on('after:render', function() {
canvas.contextContainer.strokeStyle = '#555';
canvas.forEachObject(function(obj) {
var bound = obj.getBoundingRect();
canvas.contextContainer.strokeRect(
bound.left,
bound.top,
bound.width,
bound.height
);
})
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.0.0-rc.3/fabric.js"></script>
<canvas id="canvas" width="800" height="500" style="border:1px solid #ccc"></canvas>
You should use the center to align them, that is not gonna change.
to align the bounding box at left 5 for example:
1) calculate bounding box.
2) set the position of the object to 5 + bb.width/2 considering center.
In this case the bounding rects get aligned.
var canvas = this.__canvas = new fabric.Canvas('canvas');
//fabric.Object.prototype.transparentCorners = false;
var red = new fabric.Rect({
id: 1,
left: 100,
top: 50,
width: 100,
height: 100,
fill: 'red',
angle: 0,
padding: 10
});
canvas.add(red);
var green = new fabric.Rect({
id: 2,
left: 250,
top: 180,
width: 100,
height: 100,
fill: 'green',
angle: 45,
padding: 10
});
canvas.add(green);
//ALIGN EVERYTHING TO 5
canvas.forEachObject(function(object) {
var bb = object.getBoundingRect();
object.setPositionByOrigin({ x: 5 + bb.width/2, y: bb.top }, 'center', 'center');
object.setCoords();
});
canvas.renderAll();
canvas.on("object:moving", function(e){
const draggableObj = e.target;
const draggableObjBound = draggableObj.getBoundingRect(true, true);
canvas.forEachObject(function(obj) {
if (obj.id !== draggableObj.id) {
var bound = obj.getBoundingRect(true, true);
if (draggableObjBound.top > bound.top - 10 && draggableObjBound.top < bound.top + 10) {
draggableObj.setPositionByOrigin({ x: draggableObj.left, y: bound.top + draggableObjBound.height/2 }, draggableObj.originX, 'center');
}
}
});
});
canvas.forEachObject(function(obj) {
var setCoords = obj.setCoords.bind(obj);
obj.on({
moving: setCoords,
scaling: setCoords,
rotating: setCoords
});
});
canvas.on('after:render', function() {
canvas.contextContainer.strokeStyle = '#555';
canvas.forEachObject(function(obj) {
var bound = obj.getBoundingRect(true, true);
canvas.contextContainer.strokeRect(
bound.left,
bound.top,
bound.width,
bound.height
);
})
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.0.0-rc.3/fabric.js"></script>
<canvas id="canvas" width="800" height="500" style="border:1px solid #ccc"></canvas>

how to render an object reappeared on the canvas

Initially I instantiated a Rect object, by controlling the object's top and left values, making it beyond the canvas area, so that the Rect object will not be rendered on the canvas. After that, change the top and left values of the Rect to make it in the area of the canvas by the event handler and then how to render the Rect object on the canvas.
the following code is a demo:
<canvas id="canvas" width="800" height="600"></canvas>
<script src="js/fabric.js"></script>
<script>
(function () {
var canvas = this.__canvas = new fabric.Canvas('canvas');
fabric.Object.prototype.transparentCorners = false;
var targetLine = [], paramsG, paramsR;
for (var k = 0; k < 20; k++) {
paramsG = {
left: 200,
top: 530 - 100 * k,
width: 20,
height: 50,
visibile: false,
fill: '#62ab59',
hasBorders: false,
lockMovementX: true,
hasControls: false
};
paramsR = {
left: 200,
top: 580 - 100 * k,
width: 20,
height: 50,
visibile: false,
fill: '#ed5d5d',
hasBorders: false,
lockMovementX: true,
hasControls: false
};
canvas.add(new fabric.Rect(paramsG), new fabric.Rect(paramsR));
}
canvas.on('mouse:down', function (e) {
if (e.target) {
targetLine = getMemberByLeft(canvas._objects, e.target);
}
})
canvas.on('object:moving', function (e) {
targetLine.forEach(function (val) {
canvas._objects[val.index].set({top: e.e.movementY + canvas._objects[val.index].top});
})
canvas.renderAll();
})
function getMemberByLeft(arr, tar) {
var returnArr = [];
arr.forEach(function (value, key) {
if (value.left == tar.left && value != tar) {
returnArr.push({data: value, index: key});
}
})
return returnArr;
}
})();
</script>
Fabric has a function to skip object rendering if they are not visible on screen, to get some more speed.
If you change top and left by code, fabric will not understand that the object is again on screen unless you call object.setCoords()
If you do not want to have this behaviour automatic you can disable it using
canvas.skipOffscreen = false;

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