Develop Reference

Trying to drag and drop onto an SVG canvas with accurate coordinates

I am trying to implement drag and drop an image element onto an SVG canvas but the elements are not in the same div. I have tried to use clientX and clientY properties but they are out by about 20 pixels when I come to drop the element. I think the problem is that the SVG coordinates work from the top of the root SVG element but drag and drop coordinates are from the visible view port. When I try to release the rock image on the canvas it just seems to go to any random place on it and sometimes off the canvas completely.
I have uploaded all my code to https://github.com/kiwiheretic/gravity
(It shouldn't be too difficult to just clone the repo and open index.html within the browser to see the problem.)
The relevant HTML code is as follows:
<div style="background-color:black; width: min-content;">
<svg id="space" width="600" height="400" xmlns="http://www.w3.org/2000/svg" onload="makeDraggable(evt)">
</svg>
</div>
<div id="object-block-1" class="objects">
<div class="box">
<img src="asteroid.png" alt="asteroid">
</div>
</div>
</div>
The relevant javascript code is:
var objblock = document.getElementById("object-block-1");
objblock.addEventListener("dragstart", function(evt) {
draggedObject = evt.target;
});
objbl
objblock.addEventListener("dragend", function(evt) {
var x = evt.clientX;
var y = evt.clientY;
var src = draggedObject.getBoundingClientRect();
console.log([x,y]);
var space = document.getElementById("space");
var tgt = space.getBoundingClientRect();
if (doesPointCollide(x,y,tgt)) {
//asteroid = makeAsteroid(x, y, 50, 50);
//space.appendChild(asteroid);
}
});
objblock.addEventListener("drag", function(evt) {
var space = document.getElementById("space");
var rect = space.getBoundingClientRect();
var src = draggedObject.getBoundingClientRect();
var x = (src.x - rect.x) + evt.clientX;
var y = (src.y + rect.y) + evt.clientY;
document.getElementsByName("drag-x")[0].value = parseInt(x);
document.getElementsByName("drag-y")[0].value = parseInt(y);
});
I am using the right hand input boxes as kind of a debugging aid. I am not sure why drag-x and drag-y are not resolving to suitable SVG coordinates within the canvas and what needs to be done to fix that.
Any idea what javascript mouse event attributes and element attributes to work out my SVG coordinates for drag and drop?

Is SVG resizing this hard ? What am I missing?

I am trying to write code that resizes an SVG overlay on top of an image. The server I am working with returns both the image and via an API, a list of polygon points I need to overlay on top of the image.
This is what it should look like (the image below is a correctly aligned SVG layer). The image size is 1280x720 (I've scaled it down)
What I need to do in my app (ionic v1 app) is to make sure the SVG overlay resizes as the browser window resizes and it seems to be very hard. Here is my approach:
I am trapping a window resize event and when the image is resized, I scale the SVG polygon points relative to the size of the drawn window as it seems there is really no way to "automatically" scale the SVG by the browser like it does with an image.
Here is my code pen as you see it doesn't work as intended when I rescale (and for that matter in when its full size the overlays are not accurate). The overlays don't look accurate and when I resize it all messed up. Can someone help?
Given SO needs a code block for codepen links here it is, but its just easier to look at the codepen if you want to run it
CSS:
.imagecontainer{position:relative; margin:0 auto;}
.zonelayer
{
position:absolute;
top:0;
left:0;
background:none;
}
.zonelayer polygon {
fill-opacity: 0.25;
stroke-width: 2px;
}
.Active {
stroke: #ff0000;
fill: #ff0000;
}
HTML code:
<ion-content>
image:{{disp}}<br/>
<small>points: <span ng-repeat="item in zoneArray">{{item}}</span></small>
<div class="imagecontainer">
<img id="singlemonitor" style="width:100vw; height:100vh;object-fit:contain" ng-src="http://m9.i.pbase.com/o9/63/103963/1/164771719.2SfdldRy.nphzms.jpeg" />
<div class="zonelayer">
<svg ng-attr-width="{{cw}}" ng-attr-height="{{ch}}" class="zonelayer" ng-attr-viewBox="0 0 {{cw}} {{ch}}">
<polygon ng-repeat="item in zoneArray" ng-attr-points="{{item}}" class="Active"/> </polygon>
</svg>
</div>
</div>
</ion-content>
JS controller:
window.addEventListener('resize', liveloaded);
liveloaded();
// credit: http://stackoverflow.com/questions/41411891/most-elegant-way-to-parse-scale-and-re-string-a-string-of-number-co-ordinates?noredirect=1#41411927
function scaleCoords(string, sx, sy) {
var f = [sx, sy];
return string.split(' ').map(function (a) {
return a.split(',').map(function (b, i) {
return Math.round(b * f[i]);
}).join(',');
}).join(' ');
}
function liveloaded()
{
$timeout (function () {
console.log ("IMAGE LOADED");
var img =document.getElementById("singlemonitor");
//var offset = img.getBoundingClientRect();
$scope.cw = img.clientWidth;
$scope.ch = img.clientHeight;
$scope.vx = img.offsetWidth;
$scope.vy = img.offsetHeight;
var rect = img.getBoundingClientRect();
//console.log(rect.top, rect.right, rect.bottom, rect.left);
$scope.disp = img.clientWidth+ "x"+img.clientHeight + " with offsets:"+$scope.vx+"/"+$scope.vy;
$scope.zoneArray = [
"598,70 700,101 658,531 516,436",
"531,243 687,316 663,593 360,717 191,520",
"929,180 1108,248 985,707 847,676",
"275,17 422,45 412,312 271,235",
];
var ow = 1280;
var oh = 720;
for (var i=0; i < $scope.zoneArray.length; i++)
{
var sx = $scope.cw/ow;
var sy = $scope.ch/oh;
$scope.zoneArray[i] = scaleCoords($scope.zoneArray[i],sx,sy);
console.log ("SCALED:"+$scope.zoneArray[i]);
}
});
}

There are a couple of issues with your code.
The main problem is you can't use ng-attr-viewBox, because angular will "normalise" the attribute to lower case. It turns the attribute into viewbox (lower case B) which is (currently) invalid. viewBox is case sensitive.
The solution is to use a special trick of Angular to preserve camel-case. If you use ng-attr-view_box, it will generate the correctly camel-cased attribute name of viewBox.
<svg width="100vw" height="100vh" class="zonelayer" ng-attr-view_box="0 0 {{cw}} {{ch}}">
The other thing is that you are using the wrong width and height values for the viewBox. You need to use the natural/intrinsic image dimensions in your viewBox.
$scope.cw = img.naturalWidth;
$scope.ch = img.naturalHeight;
Link to updated code pen

How to get the click coordinates relative to SVG element holding the onclick listener?

I haven't been able to calculate the click coordinates (x and y) relative to the element triggering the event. I have not found an easy example online.
I have a simple svg (with 100px left margin) in an HTML page. It contains a group (translated 30px 30px) which has an onclick listener attached. And inside that group I have a rect with 50px width and height.
After I click any part of the group element, I get an event object with coordinates relative to the HTML page (evt.clientX and evt.clientY).
What I need to know is where exactly the user clicked inside the group element (the element holding the onclick listener).
How do I convert clientX and clientY coordinates to the group element coordinates. So say, if I click the top leftmost part of the rect it should give me x=0 and y=0.
Here is currently what I have:
<!DOCTYPE html>
<html>
<head>
<style>
body{
background:black;
}
svg{
fill:white;
background:white;
position: absolute;
top:100px;
left:100px;
}
</style>
<script>
function clicked(evt){
alert("x: "+evt.clientX+" y:"+evt.clientY);
}
</script>
</head>
<body>
<div>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="200" height="200">
<g transform="translate(30 30)" onclick="clicked(evt)">
<rect x="0" y="0" width="50" height="50" fill="red"/>
</g>
</svg>
</div>
</body>
</html>

Tolokoban's solution has the limitation that it doesn't work if your viewBox deviates from the default, that is if it is different from viewBox="0 0 width height". A better solution that also takes viewBox into account is this:
var pt = svg.createSVGPoint(); // Created once for document
function alert_coords(evt) {
pt.x = evt.clientX;
pt.y = evt.clientY;
// The cursor point, translated into svg coordinates
var cursorpt = pt.matrixTransform(svg.getScreenCTM().inverse());
console.log("(" + cursorpt.x + ", " + cursorpt.y + ")");
}
(Credit goes to Smerk, who posted the code)
If the viewBox is not set or set to the default, this script will return the same values as Tolokoban's script. But if you have an SVG like <svg width="100px" height="100" viewBox="0 0 200 200">, only this version will give you the correct results.

Try to use getBoundingClientRect(): http://jsfiddle.net/fLo4uatw/
function clicked(evt){
var e = evt.target;
var dim = e.getBoundingClientRect();
var x = evt.clientX - dim.left;
var y = evt.clientY - dim.top;
alert("x: "+x+" y:"+y);
}

The proposed solutions are great, but they won't work in all scenarios.
The OP's post is titled
How to get the click coordinates relative to SVG element holding the
onclick listener?
So if you put the onclick listener onto your root svg element, whenever you click on any of its child elements, getBoundingClientRect will give you the child's Rect and you won't get the click coordinates relative to the root svg.
This was my case as I needed the coordinates relative to the root at all times, and the solution that worked for me was to use e.target.farthestViewportElement. Here's an excerpt from my (JSX) code:
const onClickSvg = e => {
const { farthestViewportElement: svgRoot } = e.target;
const dim = svgRoot.getBoundingClientRect();
const x = e.clientX - dim.left;
const y = e.clientY - dim.top;
console.log(`x: ${x}, y: ${y}`);
};
<svg onClick={onClickSvg}>...</svg>

Adding notes after many researchs (and fails!).
For a css translated svg, to get the coordinates of a clicked point for drawing.
In my case, using a mouse wheel event to translateX, so the actual rendering depends of the screen size and of the actual translated value.
I recommend for your use case to make a little drawing like the following, it will help a lot for figuring out what's going on.
Let's say my svg has for id: shoke
To get the total computed width, in pixels:
shoke.getBoundingClientRect()["width"]
Need to know the actual translateX value. (From the right, so it is a negative number, on this case)
shoke.style.transform.substr(11).slice(0,-3)
Note that it return a string and not an integer, so:
+shoke.style.transform.substr(11).slice(0,-3)
Now to get the coordinates of the mouse, related to the pixel x0 of the screen.
let pt = document.querySelector('svg').createSVGPoint();
pt.matrixTransform(shoke.getScreenCTM().inverse())["x"]
So, at the end, to obtain the precise x point:
svg_width - (svg_width + translated) + from_pixel x0 of the screen_click
Is something like this:
shoke.getBoundingClientRect()["width"] - (shoke.getBoundingClientRect()["width"] + +shoke.style.transform.substr(11).slice(0,-3)) + pt.matrixTransform(shoke.getScreenCTM().inverse())["x"]

createSVGPoint is deprecated according to Mozilla. Use static method of DOMPoint.fromPoint(svg_element);
function dom_track_click(evt) {
//<svg onclick='dom_track_click(event); >
let pt = DOMPoint.fromPoint(document.getElementById('svg_canvas'));
pt.x = evt.clientX;
pt.y = evt.clientY;
// The cursor point, translated into svg coordinates
let cursorpt = pt.matrixTransform(document.getElementById('svg_canvas').getScreenCTM().inverse());
console.log("(" + cursorpt.x + ", " + (cursorpt.y) + ")");
}

How would you create a JQuery / svg click-drag select outline effect?

Not sure exactly what to call it, but I am looking for a way to create a dotted outline/selection box effect via javascript/svg when you click and drag over an area, and then goes away on mouseUp (that could be added if it wasn't an original part) .
A jQuery library would be nice if it exists. I've done some looking around, and haven't found exactly what I am looking for.
I guess the theory would be get the coord from the first click, track the mouse coord moment and adjust the box accordingly.
But not writing it from scratch would be nice.

Here's a demo I made just for you :)
Demo (Static): http://jsfiddle.net/HNH2f/1/
Demo (Animated): http://jsfiddle.net/HNH2f/2/
You can use CSS to control the visual style of the marquee.
You can pass one or two functions to the trackMarquee method; both will be called with four arguments: the x1,y1,x2,y2 bounds of the marquee. The first function will be called when the marquee is released. The second function (if present) will be called each time the marquee moves (so that you can, for example, calculate what items are within that bounding box).
When you start dragging on the SVG document (or whatever element you choose to track) it will create a <rect class="marquee" />; during dragging it will adjust the size of the rectangle. Use CSS (as seen in the demo) to style this rectangle however you want. I'm using the stroke-dasharray property to make the border dotted.
For Stack Overflow posterity, here's the code (on the off chance that JSFiddle is down):
(function createMarquee(global){
var svgNS = 'http://www.w3.org/2000/svg',
svg = document.createElementNS(svgNS,'svg'),
pt = svg.createSVGPoint();
// Usage: trackMarquee( mySVG, function(x1,y1,x2,y2){}, function(x1,y1,x2,y2){} );
// The first function (if present) will be called when the marquee is released
// The second function (if present) will be called as the marquee is changed
// Use the CSS selector `rect.marquee` to select the marquee for visual styling
global.trackMarquee = function(forElement,onRelease,onDrag){
forElement.addEventListener('mousedown',function(evt){
var point0 = getLocalCoordinatesFromMouseEvent(forElement,evt);
var marquee = document.createElementNS(svgNS,'rect');
marquee.setAttribute('class','marquee');
updateMarquee(marquee,point0,point0);
forElement.appendChild(marquee);
document.documentElement.addEventListener('mousemove',trackMouseMove,false);
document.documentElement.addEventListener('mouseup',stopTrackingMove,false);
function trackMouseMove(evt){
var point1 = getLocalCoordinatesFromMouseEvent(forElement,evt);
updateMarquee(marquee,point0,point1);
if (onDrag) callWithBBox(onDrag,marquee);
}
function stopTrackingMove(){
document.documentElement.removeEventListener('mousemove',trackMouseMove,false);
document.documentElement.removeEventListener('mouseup',stopTrackingMove,false);
forElement.removeChild(marquee);
if (onRelease) callWithBBox(onRelease,marquee);
}
},false);
};
function callWithBBox(func,rect){
var x = rect.getAttribute('x')*1,
y = rect.getAttribute('y')*1,
w = rect.getAttribute('width')*1,
h = rect.getAttribute('height')*1;
func(x,y,x+w,y+h);
}
function updateMarquee(rect,p0,p1){
var xs = [p0.x,p1.x].sort(sortByNumber),
ys = [p0.y,p1.y].sort(sortByNumber);
rect.setAttribute('x',xs[0]);
rect.setAttribute('y',ys[0]);
rect.setAttribute('width', xs[1]-xs[0]);
rect.setAttribute('height',ys[1]-ys[0]);
}
function getLocalCoordinatesFromMouseEvent(el,evt){
pt.x = evt.clientX; pt.y = evt.clientY;
return pt.matrixTransform(el.getScreenCTM().inverse());
}
function sortByNumber(a,b){ return a-b }
})(window);

You are lucky I just made this myself. I'm using jQuery SVG plugin ( http://keith-wood.name/svg.html )
$("#paper2").mousedown(function(ev) {
ev.preventDefault();
var pX= (ev.pageX - this.offsetLeft) * viewBox[2]/parseInt($("#paper2").css("width"));
var pY= (ev.pageY - this.offsetTop) * viewBox[3]/parseInt($("#paper2").css("height"));
var rect = svg2.rect(
pX, //X
pY, //Y
1,1, //width and height
{ //Settings, you can make the box dotted here
fill: 'black', "fill-opacity": 0.3, stroke: 'red', strokeWidth: 3, id:rect
}
)
$("#paper2").mousemove(function(ev) {
ev.preventDefault();
var rect= $('#rect');
var pX= (ev.pageX - this.offsetLeft) * viewBox[2]/parseInt($("#paper2").css("width")) - rect.attr("x");
var pY= (ev.pageY - this.offsetTop) * viewBox[3]/parseInt($("#paper2").css("height")) - rect.attr("y");
rect.attr("width", pX);
rect.attr("height", pY);
});
$("#paper2").mouseup(function(ev) {
ev.preventDefault();
var div= $("#paper2");
div.unbind('mousemove');
div.unbind('mouseup');
})
});
paper2 is a div in which I have an svg element (so the svg element and the div have the same height/width). This is how I created the svg2 element:
var svg2;
var root2;
$(document).ready(function() {
$("#paper2").svg({
onLoad: function() {
svg2= $("#paper2").svg('get');
svg2.configure({id: 'svg2'});
var div= $("#paper2");
root2= svg2.root();
$("#svg2").attr("viewBox", viewBox[0]+','+viewBox[1]+','+viewBox[2]+','+viewBox[3]);
},
settings: {}
});
}
If you not using viewbox on the svg element you don't need this on the calculations:
* viewBox[2]/parseInt($("#paper2").css("*****"));
viewbox[2] would be the viewbox width and viewbox[3] would be the viewbox height.

SVG - From Window coordinates to ViewBox coordinates

Basically I have an svg "SecondSVG" into an svg "FirstSVG" into an svg "MainSVG".Every svg has its own ViewBox. This page can be loaded anywhere on the screen by another page.
So basically how can i find the screen x for viewBox for"SecondSVG" knowing that this svg can be loaded basically anywhere based on the calling page?
event.clientX gives myself the x coordinate for the screen. If I don't know the coordinate for ViewBox of "SecondSVG" then how can I find out the x coordinate inside the ViewBox of "SecondSVG"?
I am using Firefox 3.6.3 and I do have an event object from which I can extract clientX, clientY and other coordinates that are relative to the screen. However what I need are the coordinates inside the ViewBox.

function click(evt)
{
var root = document.getElementById('your svg');
var uupos = root.createSVGPoint();
uupos.x = evt.pageX;
uupos.y = evt.pageY;
var ctm = evt.target.getScreenCTM();
if (ctm = ctm.inverse())
uupos = uupos.matrixTransform(ctm);
///the new x y are : uupos.x , uupos.y
}