Develop Reference

SVG arc slider for range input

My goal is to design an arc slider which looks something like that
I have the following structure of the template
<svg width="500" height="300">
<path id="track" stroke="lightgrey" fill="transparent" stroke-width="20" d="
M 50 50
A 90 90 0 0 0 300 50
"/>
<path id="trackFill" fill="cyan" stroke-width="20" d="
M 50 50
A 90 90 0 0 0 [some dynamic value?] [some dynamic value?]
"/>
<circle id="knob" fill="lightblue" cx="[dynamic, initial - 50]" cy="[dynamic, initial - 50]" r="25"/>
</svg>
knob - the control which user is supposed to drag in order to change the value
track - the full arc of the slide
trackFill - the portion of the slider path before the knob
Is it possible to make trackFill cover the portion of the slider before the knob as it is being dragged along the slider curve? If so which APIs or CSS rules will help me to achieve such a result?

Is it something like this you are after?
let svg = document.getElementById("slider");
let trackFill = document.getElementById("trackFill");
let knob = document.getElementById("knob");
let isDragging = false;
let sliderDragOffset = {dx: 0, dy: 0};
let ARC_CENTRE = {x: 175, y: 50};
let ARC_RADIUS = 125;
let sliderValue = 0;
setSliderValue(sliderValue);
function setSliderValue(value)
{
// Limit value to (0..sliderMax)
let sliderMax = track.getTotalLength();
sliderValue = Math.max(0, Math.min(value, sliderMax));
// Calculate new position of knob
let knobRotation = sliderValue * Math.PI / sliderMax;
let knobX = ARC_CENTRE.x - Math.cos(knobRotation) * ARC_RADIUS;
let knobY = ARC_CENTRE.y + Math.sin(knobRotation) * ARC_RADIUS;
// Adjust trackFill dash patter to only draw the portion up to the knob position
trackFill.setAttribute("stroke-dasharray", sliderValue + " " + sliderMax);
// Update the knob position
knob.setAttribute("cx", knobX);
knob.setAttribute("cy", knobY);
}
knob.addEventListener("mousedown", evt => {
isDragging = true;
// Remember where we clicked on knob in order to allow accurate dragging
sliderDragOffset.dx = evt.offsetX - knob.cx.baseVal.value;
sliderDragOffset.dy = evt.offsetY - knob.cy.baseVal.value;
// Attach move event to svg, so that it works if you move outside knob circle
svg.addEventListener("mousemove", knobMove);
// Attach move event to window, so that it works if you move outside svg
window.addEventListener("mouseup", knobRelease);
});
function knobMove(evt)
{
// Calculate adjusted drag position
let x = evt.offsetX + sliderDragOffset.dx;
let y = evt.offsetY + sliderDragOffset.dy;
// Position relative to centre of slider arc
x -= ARC_CENTRE.x;
y -= ARC_CENTRE.y;
// Get angle of drag position relative to slider centre
let angle = Math.atan2(y, -x);
// Positions above arc centre will be negative, so handle them gracefully
// by clamping angle to the nearest end of the arc
angle = (angle < -Math.PI / 2) ? Math.PI : (angle < 0) ? 0 : angle;
// Calculate new slider value from this angle (sliderMaxLength * angle / 180deg)
setSliderValue(angle * track.getTotalLength() / Math.PI);
}
function knobRelease(evt)
{
// Cancel event handlers
svg.removeEventListener("mousemove", knobMove);
window.removeEventListener("mouseup", knobRelease);
isDragging = false;
}
<svg id="slider" width="500" height="300">
<g stroke="lightgrey">
<path id="track" fill="transparent" stroke-width="20" d="
M 50 50
A 125 125 0 0 0 300 50
"/>
</g>
<use id="trackFill" xlink:href="#track" stroke="cyan"/>
<circle id="knob" fill="lightblue" cx="50" cy="50" r="25"/>
</svg>
I've kept this code simple for clarity, but at the expense of some limitations.
It assumes there is only one slider per page. If you need more than that, you will have to keep the slider-specific values (eg sliderValue and, isDragging) separate. You could use data attributes for that. You would also need to switch from accessing the SVG elements via id attributes to another way (eg. class attributes), because id attributes must be unique on the page.

Here is a simple example:
const radius = 50;
const offsetX = 10;
const offsetY = 10;
// 0 <= pos <= 1
const setSliderPos = (svg, pos) => {
const angle = Math.PI * pos;
const x = offsetX + radius - Math.cos(angle) * radius;
const y = offsetY + Math.sin(angle) * radius;
svg.select('.knob').attr('cx', x).attr('cy', y);
svg.select('.first').attr('d', `M ${offsetX},${offsetY} A ${radius},${radius} 0 0 0 ${x},${y}`);
svg.select('.second').attr('d', `M ${x},${y} A ${radius},${radius} 0 0 0 ${offsetX + radius * 2},${offsetY}`);
}
setSliderPos(d3.select('#svg-1'), 0.3);
setSliderPos(d3.select('#svg-2'), 0.6);
setSliderPos(d3.select('#svg-3'), 1);
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/5.7.0/d3.min.js"></script>
<svg id="svg-1" width="150" height="80">
<path class="first" stroke-width="5" stroke="lightblue" fill="none"/>
<path class="second" stroke-width="5" stroke="cyan" fill="none"/>
<circle class="knob" r="10" fill="lightblue"/>
</svg>
<svg id="svg-2" width="150" height="80">
<path class="first" stroke-width="5" stroke="lightblue" fill="none"/>
<path class="second" stroke-width="5" stroke="cyan" fill="none"/>
<circle class="knob" r="10" fill="lightblue"/>
</svg>
<svg id="svg-3" width="150" height="80">
<path class="first" stroke-width="5" stroke="lightblue" fill="none"/>
<path class="second" stroke-width="5" stroke="cyan" fill="none"/>
<circle class="knob" r="10" fill="lightblue"/>
</svg>

To mark the progress you can use stroke-dasharray with a percentage; for example
<g stroke="lightgrey">
<path id="track" fill="transparent" stroke-width="20"
stroke-dasharray="40% 60%"
d="M 50 50 A 125 125 0 0 0 300 50"/>
</g>
This will show 40% of the arc and hide 60% of the arc.
If you need to use two colors, for example the whole arc in grey and the progress in black, you need to use two arcs on top of one another; the one at the bottom would be the one you already have, and the one at the top would have a stroke in black and use stroke-dasharray as shown.

Getting the coordinates of a moving SVG Circle which is moving over a path set in animateMotion

I need to check the response of a user by tracking the mouse movement over a moving object (in this case a circle). If the mouse is not over the circle I need to calculate the offset by comparing the mouse coordinates and the circle coordinates.
But whenever I check the circle values, they are not changing and will stay on their initial value.
Here's a simple example:
function clickCircle() {
var circle = document.getElementById("circle");
console.log('baseVal x: ' + circle.cx.baseVal.value);
console.log('animVal x: ' + circle.cx.animVal.value);
}
<p>Click on the moving circle</p>
<svg width="1200" height="1200">
<circle id="circle" cx="60" cy="60" r="20" fill="green" onclick="clickCircle();">
<animateMotion id="ani" dur="10s" repeatCount="indefinite"
path="M20, 60 C20,
-50 180, 150 180,
60 C180-60 20,
150 20, 60 z" />
</circle>
</svg>
Does anybody have any idea on how to get the coordinates from a moving circle that is being animated with animateMotion?

You could drag in an animation Icon, and track its properties
Or with JavaScript you calculate its center x,y position with:
let {width,height} = circle.getBBox();
let {x,y} = circle.getBoundingClientRect();
x = x + width/2;
y = y + height/2;
Also read: https://schneide.blog/2018/03/05/some-tricks-for-working-with-svg-in-javascript/
note! this code below will forever add circle Nodes!
<style> svg { width: 300px } </style>
<svg viewBox="0 0 300 200">
<rect width="100%" height="100%" fill="lightgreen"></rect>
<text x=10 y="20">Click the circle!</text>
<circle id="circle" cx="40" cy="40" r="40" fill="green"
onclick="clickCircle(event)">
<animateMotion id="ani" dur="10s" repeatCount="indefinite" path="m20 40c0-110 160 90 160 0c0-120-160 90-160 0z" />
</circle>
<text id="position" x="200" y="20">21</text>
</svg>
<script>
function clickCircle(evt) {
point("gold");
}
function point(color) {
let circle = document.getElementById("circle");
let {width,height} = circle.getBBox();
let {x,y} = circle.getBoundingClientRect();
let c = document.createElementNS("http://www.w3.org/2000/svg", "circle");
x = x + width/2;
y = y + height/2;
c.setAttribute("cx", x);
c.setAttribute("cy", y);
c.setAttribute("r", color == "black" ? 3 : 6);
c.setAttribute("fill", color);
circle.parentNode.append(c);
position.innerHTML = `${~~x} , ${~~y}`;
}
setInterval(() => point("black"), 250);
</script>
Or try the JSFiddle: https://jsfiddle.net/dannye/ph705b49/
Dan was Authorware toch heel wat makkelijker...
Alles goed?

Find intersect line with circle is not working in Javascript

I followed the formula to find intersect line with circle. But it does not work. Here is my code.
<svg height="397" width="851">
<circle cx="334.4" cy="198.5" r="150.8" stroke="black" stroke-width="3" fill="red" />
<line x1="485.60978255954285" y1="231.75390342766823" x2="488.9584783979701" y2="231.75390342766823" style="stroke:rgb(255,0,0);stroke-width:2" />
Sorry, your browser does not support inline SVG.
</svg>
<script>
var line1point= {x: 485.60978255954285, y: 231.75390342766823};
var line2point= {x: 488.9584783979701, y: 231.75390342766823};
var center = {x: 334.4, y: 198.5};
var intersect = inCircle(line1point, line2point, center, 150.8);
alert(intersect);
function inCircle (line1point, line2point, center, r){
var l1 = line1point, l2 = line2point, c = center;
return (Math.abs((l2.x - l1.x) * c.x + c.y * (l1.y - l2.y) + (l1.x - l2.x) * l1.y + (l1.y - l2.y) * c.y)
/ Math.sqrt(((l2.x - l1.x) * (l2.x - l1.x)) + ((l1.y - l2.y) *(l1.y - l2.y))) <= r);
}
</script>
Fiddle Link
I tried the formula given in this forum second answer. Stackexchange link

Animate svg elements with Javascript and JQuery

I'm trying to animate the following html elements to implement a functionality similar to a volume wheel.
<svg id="circle_svg" width="200" height="175">
<circle cx="100" cy="85" r="75" stroke="black" stroke-width="2" fill="lightgray"/>
<line id="line_alpha" x1="100" y1="85" x2="100" y2="160" style="stroke:rgb(0,0,255);stroke-width:2"/>
<circle id="dot_alpha" cx="100" cy="160" r="10" stroke="black" stroke-width="2" fill="red"/>
</svg>
The basic idea is that clicking on the red dot and moving the mouse around should result in the following behavior:
The red dot moves along the circle (even if mouse doesn't stay exactly on it).
The end point of the line on the circle follows the red dot.
A number shown somewhere else in the page gets incremented or decremented with the amount of angular displacement.
I found a demo online that allows to drag an svg circle all around the page, by binding the elements of interest to mousedown and mouseup events and rewriting the attribute cx and cy of the circle to the current location of the mouse.
However when testing the code on jsfiddle with my example (or even with the original code) something is not working. Could you please take a look and give me advice on what might be going wrong?
Jsfiddle my settings
Jsfiddle original settings

I was able to find the solution to my question (thanks to a friend) and will post it as reference for others:
The main problem with pasting the code from this online demo into jsfiddle is that the order in which JavaScript libraries and functions is not predictable.
So some binding might be called before the binded function is defined.
Also, the code from the demo is more complicated that what I needed.
Here is the code solution on jsfiddle
Below is a working snippet for SO site
var dragging = false
var updateGraphics = function (e) {
if (dragging) {
var parentOffset = $('#wheel').offset();
var relX = e.pageX - parentOffset.left;
var relY = e.pageY - parentOffset.top;
var cx = +$('#circle').attr('cx')
var cy = +$('#circle').attr('cy')
var r = +$('#circle').attr('r')
var dx = relX - cx
var dy = relY - cy
//var dx = e.clientX - cx
//var dy = e.clientY - cy
console.debug('cx: ' + cx);
console.debug('cy: ' + cy);
console.debug('dx: ' + dx);
console.debug('dy: ' + dy);
console.debug('clientX: ' + e.clientX);
console.debug('clientY: ' + e.clientY);
console.debug('relX: ' + relX);
console.debug('relY: ' + relY);
var a = Math.atan2(dy, dx)
var dotX = cx + r * Math.cos(a)
var dotY = cy + r * Math.sin(a)
$('#dot').attr('cx', dotX);
$('#dot').attr('cy', dotY);
$('#line_2').attr('x2', dotX);
$('#line_2').attr('y2', dotY);
}
}
$('svg').on('mousedown', function (e) {
dragging = true
updateGraphics(e)
})
$('svg').on('mouseup', function (e) {
dragging = false
})
$('svg').on('mousemove', updateGraphics)
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<svg id="wheel" width="200" height="175" style="background-color:lightgreen;">
<circle id="circle" cx="100" cy="85" r="75" stroke="black" stroke-width="2" fill="lightgray"/>
<line id="line_1" x1="100" y1="85" x2="100" y2="160" stroke-dasharray="15,15" style="stroke:rgb(255,0,0);stroke-width:2"/>
<line id="line_2" x1="100" y1="85" x2="100" y2="160" style="stroke:rgb(0,0,255);stroke-width:2"/>
<circle id="dot" cx="100" cy="160" r="10" stroke="black" stroke-width="2" fill="red"/>
</svg>

Raphael JS Question

I am following a tutorial from netuts about raphael js and I dont understand one of the examples, could some one possibly explain this to me in plainer english. I know I should learn more about javascript first.
for(var i = 0; i < 5; i+=1) {
var multiplier = i*5;
paper.circle(250 + (2*multiplier), 100 + multiplier, 50 - multiplier); }
Thanks! Very Much

The code will create five circles
for(var i = 0; i < 5; i+=1) { // loop five times => create five circles
var multiplier = i*5; // multiply i to increase the effect in the next lines
paper.circle( 250 + (2*multiplier), // the x coordinate of the new circle
100 + multiplier, // the y coordinate
50 - multiplier); // the radius
}
Results in this SVG element:
<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="556" height="109">
<desc>Created with Raphaël</desc>
<defs/>
<circle cx="250" cy="100" r="50" fill="none" stroke="#000"/>
<circle cx="260" cy="105" r="45" fill="none" stroke="#000"/>
<circle cx="270" cy="110" r="40" fill="none" stroke="#000"/>
<circle cx="280" cy="115" r="35" fill="none" stroke="#000"/>
<circle cx="290" cy="120" r="30" fill="none" stroke="#000"/>
</svg>

for(var i = 0; i < 5; i+=1) {
Iterate 5 times. Store the number of times iterated so far in the variable i. The "{" begins the loop.
var multiplier = i * 5;
Multiply i by 5 and store in a variable called multiplier.
paper.circle(250 + (2*multiplier), 100 + multiplier, 50 - multiplier);
Draw a circle with an x coordinate at 250 plus twice the multiplier, a y coordinate at 100 plus the multiplier and with a radius of 50 minus the multiplier. (Essentially a fancy way of getting distinct circles.)
}
End the loop.