I'm just starting with fabric.js and I wonder if there is a way to create a canvas in such a way that I can work with cartesian coordinates? For example, I want a circle that I create at (0,0) to show up in the center of my canvas that reaches from -400 to 400 on the x-axis and -400 to 400 on the y.axis, with higher values of y going up and higher values of x going right.
Is there a way to do that without translating every position by hand?
You can use originX and originY attributes.
var obj = canvas.getObjects();
for (var i in obj) {
obj[i].set({
originX: 'left',
originY: 'top',
left: 0,
top: 0
});
}
canvas.renderAll();
Check this fiddle with examples: http://jsfiddle.net/1ow02gea/51/
You cannot change the origin of the canvas element without introducing visual artifacts. What you can do is pan the canvas to a virtual "0,0" position. Bear in mind that you will have to adjust both X_PAN_VALUE and Y_PAN_VALUE to your specific use case.
canvas.viewportTransform[4] = X_PAN_VALUE;
canvas.viewportTransform[5] = Y_PAN_VALUE;
Better late than never ;)
Related
I am taking help of sample code of Transform tutorial for rotation and position change. I am facing couple of problems.
I want to perform rotation on door and window. Currently axis of rotation pass through center. How can I change to rotate a object from axis passing through its side.
For position change > when I change position lets say for a window in any direction, it moves but it is visible on wall. I want it hide when window collide with wall.
1/ Here is a code snippet that illustrates how to rotate elements (fragments), for a more complete sample take a look at this article: Rotate Components Control for the Viewer
rotateFragments (model, fragIdsArray, axis, angle, center) {
var quaternion = new THREE.Quaternion()
quaternion.setFromAxisAngle(axis, angle)
fragIdsArray.forEach((fragId, idx) => {
var fragProxy = this.viewer.impl.getFragmentProxy(
model, fragId)
fragProxy.getAnimTransform()
var position = new THREE.Vector3(
fragProxy.position.x - center.x,
fragProxy.position.y - center.y,
fragProxy.position.z - center.z)
position.applyQuaternion(quaternion)
position.add(center)
fragProxy.position = position
fragProxy.quaternion.multiplyQuaternions(
quaternion, fragProxy.quaternion)
if (idx === 0) {
var euler = new THREE.Euler()
euler.setFromQuaternion(
fragProxy.quaternion, 0)
this.emit('rotate', {
dbIds: this.selection.dbIdArray,
fragIds: fragIdsArray,
rotation: euler,
model
})
}
fragProxy.updateAnimTransform()
})
}
2/ When you transform the geometry, you are just moving triangles around, there is no built-in logic that will hide components because they overlap, you will need to implement that yourself. You should be able to find Three.js code that computes if two meshes intersect (triangle-triangle intersection algorithm) and run that against the component you are moving and all walls that are around. Here is something that can put you on tracks: How to detect collision in three.js?
Hope that helps
I am working on custom product designer which uses Fabric.js. I want to rotate all objects of canvas at once by pressing one button (rotate left, rotate right).
I have achieved this using this code :
stage.forEachObject(function(obj){
obj.setAngle(rotation).setCoords();
});
stage.renderAll();
But it has one bug that every element rotates with its own center point. I want that every element rotates with respect to whole canvas element.
Grouping and rotating the group did not work so well for me. Here is another solution based on this js fiddle.
rotateAllObjects (degrees) {
let canvasCenter = new fabric.Point(canvas.getWidth() / 2, canvas.getHeight() / 2) // center of canvas
let radians = fabric.util.degreesToRadians(degrees)
canvas.getObjects().forEach((obj) => {
let objectOrigin = new fabric.Point(obj.left, obj.top)
let new_loc = fabric.util.rotatePoint(objectOrigin, canvasCenter, radians)
obj.top = new_loc.y
obj.left = new_loc.x
obj.angle += degrees //rotate each object buy the same angle
obj.setCoords()
});
canvas.renderAll()
},
You could add all the objects to a group an then rotate the group. This way you can also set the center for rotation.
This is how it could be solved
function rotate(a) {
var group = new fabric.Group(canvas.getObjects());
//angle is var with scope out of this function,
//so you can use this function as rotate(90) and keep rotating
angle = (angle + a) % 360;
group.rotate(angle);
canvas.centerObject(group);
group.setCoords();
canvas.renderAll();
}
FabricJS rotate everything and maintain the relative position also.
You can download the files here - https://drive.google.com/file/d/1UV1nBdfBk6bg9SztyVoWyLJ4eEZJgZRf/view?usp=sharing
I'm working on a paint application and I'm trying to centre the canvas onto the middle of the screen . Any attempts I made the detection was off(still at the top left of the screen) but it was visually appearing in the centre of the screen.
Basically it wont draw onto the canvas when I moved it to the centre of the screen.
Any help would be much appreciated , Thanks....
I HAVE MY CODE BELOW ...
It's not clear from your question how you're centring it, but you need to account for any offset of elements which contain your canvas when you attempt to map the mouse position to a position on the canvas. You can do this by including the offsetLeft and offsetTop values (see docs) of the containing element when you do your calculations.
The following will work if you're offsetting the position of the div which wraps the canvas (which I've given an id to make it easier to reference):
function move(e) {
// Get the div containing the canvas. Would be more efficient to set this once on document load
var container = document.getElementById('container');
if((e.button == 0) && (mouseIsDown)) {
g.beginPath();
document.onselectstart = function(){ return false; }
//g.fillStyle = "red";
// Account for the offset of the parent when drawing to the canvas
g.arc((e.x - container.offsetLeft) - brush, (e.y - container.offsetTop) - brush, brush, 0, Math.PI * 2);
g.fill();
g.closePath();
}
}
And a simplistic demo using your fiddle here.
I suppose this doesn't work because canvas is drawing a bitmap of a vector (and a bitmap is not a path).
Even if it did work, the bitmap is likely always has a rectangular permitter.
Is there any way to leverage something like isPointInPath when using drawImage?
example:
The top canvas is drawn using drawImage and isPointInPath does not work.
The bottom canvas is drawn using arc and isPointInPath works.
a link to my proof
** EDIT **
I draw a circle on one canvas, and use isPointInPath to see if the mouse pointer is inside the circle (bottom canvas in my example).
I also "copy" the bottom canvas to the top canvas using drawImage. Notice that isPointInPath will not work on the top canvas (most likely due to reasons I mentioned above). Is there a work-around I can use for this that will work for ANY kind of path (or bitmap)?
A canvas context has this hidden thing called the current path. ctx.beginPath, ctx.lineTo etc create this path.
When you call ctx.stroke() or ctx.fill() the canvas strokes or fills that path.
Even after it is stroked or filled, the path is still present in the context.
This path is the only thing that isPointInPath tests.
If you want to test if something is in an image you have drawn or a rectangle that was drawn with ctx.fillRect(), that is not possible using built in methods.
Typically you'd want to use a is-point-in-rectangle function that you write yourself (or get from someone else).
If you're looking for how to do pixel-perfect (instead of just the image rectangle) hit detection for an image there are various methods of doing that discussed here: Pixel perfect 2D mouse picking with Canvas
You could try reimplementing ctx.drawImage() to always draw a box behind the image itself, like so (JSFiddle example):
ctx.customDrawImage = function(image, x, y){
this.drawImage(image, x, y);
this.rect(x, y, image.width, image.height);
}
var img1 = new Image();
img1.onload = function(){
var x = y = 0;
ctx.drawImage(img1, x, y);
console.log(ctx.isPointInPath(x + 1, y + 1));
x = 1.25 * img1.width;
ctx.customDrawImage(img1, x, y);
console.log(ctx.isPointInPath(x + 1, y + 1));
Note: you might get side effects like the rectangle appearing over the image, or bleeding through from behind if you are not careful.
To me, isPointInPath failed after canvas was moved. So, I used:
mouseClientX -= gCanvasElement.offsetLeft;
mouseclientY -= gCanvasElement.offsetTop;
I had some more challenges, because my canvas element could be rescaled. So first when I draw the figures, in my case arc, I save them in an array together with a name and draw them:
if (this.coInit == false)
{
let co = new TempCO ();
co.name= sensor.Name;
co.path = new Path2D();
co.path.arc(c.X, c.Y, this.radius, 0, 2 * Math.PI);
this.coWithPath.push(co);
}
let coWP = this.coWithPath.find(c=>c.name == sensor.Name);
this.ctx.fillStyle = color;
this.ctx.fill(coWP.path);
Then in the mouse event, I loop over the items and check if the click event is in a path. But I also need to rescale the mouse coordinates according to the resized canvas:
getCursorPosition(event) {
const rect = this.ctx.canvas.getBoundingClientRect();
const x = ((event.clientX - rect.left ) / rect.width) * this.canvasWidth;
const y = ((event.clientY - rect.top) / rect.height) * this.canvasHeight;
this.coWithPath.forEach(c=>{
if (this.ctx.isPointInPath(c.path, x, y))
{
console.log("arc is hit", c);
//Switch light
}
});
}
So I get the current size of the canvas and rescale the point to the original size. Now it works!
This is how the TempCO looks like:
export class TempCO
{
path : Path2D;
name : string;
}
This question already has answers here:
What's the best way to set a single pixel in an HTML5 canvas?
(14 answers)
Closed 7 years ago.
Drawing a line on the HTML5 canvas is quite straightforward using the context.moveTo() and context.lineTo() functions.
I'm not quite sure if it's possible to draw a dot i.e. color a single pixel. The lineTo function wont draw a single pixel line (obviously).
Is there a method to do this?
For performance reasons, don't draw a circle if you can avoid it. Just draw a rectangle with a width and height of one:
ctx.fillRect(10,10,1,1); // fill in the pixel at (10,10)
If you are planning to draw a lot of pixel, it's a lot more efficient to use the image data of the canvas to do pixel drawing.
var canvas = document.getElementById("myCanvas");
var canvasWidth = canvas.width;
var canvasHeight = canvas.height;
var ctx = canvas.getContext("2d");
var canvasData = ctx.getImageData(0, 0, canvasWidth, canvasHeight);
// That's how you define the value of a pixel
function drawPixel (x, y, r, g, b, a) {
var index = (x + y * canvasWidth) * 4;
canvasData.data[index + 0] = r;
canvasData.data[index + 1] = g;
canvasData.data[index + 2] = b;
canvasData.data[index + 3] = a;
}
// That's how you update the canvas, so that your
// modification are taken in consideration
function updateCanvas() {
ctx.putImageData(canvasData, 0, 0);
}
Then, you can use it in this way :
drawPixel(1, 1, 255, 0, 0, 255);
drawPixel(1, 2, 255, 0, 0, 255);
drawPixel(1, 3, 255, 0, 0, 255);
updateCanvas();
For more information, you can take a look at this Mozilla blog post : http://hacks.mozilla.org/2009/06/pushing-pixels-with-canvas/
It seems strange, but nonetheless HTML5 supports drawing lines, circles, rectangles and many other basic shapes, it does not have anything suitable for drawing the basic point. The only way to do so is to simulate a point with whatever you have.
So basically there are 3 possible solutions:
draw point as a line
draw point as a polygon
draw point as a circle
Each of them has their drawbacks.
Line
function point(x, y, canvas){
canvas.beginPath();
canvas.moveTo(x, y);
canvas.lineTo(x+1, y+1);
canvas.stroke();
}
Keep in mind that we are drawing to South-East direction, and if this is the edge, there can be a problem. But you can also draw in any other direction.
Rectangle
function point(x, y, canvas){
canvas.strokeRect(x,y,1,1);
}
or in a faster way using fillRect because render engine will just fill one pixel.
function point(x, y, canvas){
canvas.fillRect(x,y,1,1);
}
Circle
One of the problems with circles is that it is harder for an engine to render them
function point(x, y, canvas){
canvas.beginPath();
canvas.arc(x, y, 1, 0, 2 * Math.PI, true);
canvas.stroke();
}
the same idea as with rectangle you can achieve with fill.
function point(x, y, canvas){
canvas.beginPath();
canvas.arc(x, y, 1, 0, 2 * Math.PI, true);
canvas.fill();
}
Problems with all these solutions:
it is hard to keep track of all the points you are going to draw.
when you zoom in, it looks ugly
If you are wondering, what is the best way to draw a point, I would go with filled rectangle. You can see my jsperf here with comparison tests
In my Firefox this trick works:
function SetPixel(canvas, x, y)
{
canvas.beginPath();
canvas.moveTo(x, y);
canvas.lineTo(x+0.4, y+0.4);
canvas.stroke();
}
Small offset is not visible on screen, but forces rendering engine to actually draw a point.
The above claim that "If you are planning to draw a lot of pixel, it's a lot more efficient to use the image data of the canvas to do pixel drawing" seems to be quite wrong - at least with Chrome 31.0.1650.57 m or depending on your definition of "lot of pixel". I would have preferred to comment directly to the respective post - but unfortunately I don't have enough stackoverflow points yet:
I think that I am drawing "a lot of pixels" and therefore I first followed the respective advice for good measure I later changed my implementation to a simple ctx.fillRect(..) for each drawn point, see http://www.wothke.ch/webgl_orbittrap/Orbittrap.htm
Interestingly it turns out the silly ctx.fillRect() implementation in my example is actually at least twice as fast as the ImageData based double buffering approach.
At least for my scenario it seems that the built-in ctx.getImageData/ctx.putImageData is in fact unbelievably SLOW. (It would be interesting to know the percentage of pixels that need to be touched before an ImageData based approach might take the lead..)
Conclusion: If you need to optimize performance you have to profile YOUR code and act on YOUR findings..
This should do the job
//get a reference to the canvas
var ctx = $('#canvas')[0].getContext("2d");
//draw a dot
ctx.beginPath();
ctx.arc(20, 20, 10, 0, Math.PI*2, true);
ctx.closePath();
ctx.fill();