SVG Line with linear gradient [duplicate] - svg

Question

I'd like to put a simple loading indicator on my website that's triggered by a script. It should be a simple circle arc that's got a gradient and is spinning while the user is waiting. I haven't tried the animation part, but got stuck on the static styling for now. Here's what I've got so far:
<svg version="1.1" baseProfile="full" xmlns="http://www.w3.org/2000/svg"
width="100" height="100">
<defs>
<linearGradient id="grad1">
<stop offset="0%" stop-color="red"/>
<stop offset="100%" stop-color="red" stop-opacity="0" />
</linearGradient>
</defs>
<path d="M50 10 A40 40 0 1 0 90 50"
stroke="url(#grad1)" stroke-width="10" fill="transparent"/>
</svg>
It draws the arc, from the top edge anti-clockwise to the right edge (270°), but the gradient is wrong. Instead of following the path so that the beginning (top edge, 0°) is opaque and the end (right edge, 270°) is transparent, the resulting image of the arc stroke is coloured from left to right in screen space.
How can I make the gradient follow my arc path?

Answer 1

Mike Bostock figured out a way, though it's not easy:
https://bl.ocks.org/mbostock/4163057
Basically, this technique uses getPointAtLength to slice the stroke into many short strokes, specify interpolated color stops for each, and then apply a gradient to each short stroke between those stops.
Good luck if you're up to the challenge ;)
Edit (July 3rd, 2019):
There is now a library that will help you do exactly what you're looking for. It's not required to use D3, but you're able to if you desire. Here's a tutorial on Medium.

Answer 2

path{
fill : url(#gradient)
}
<svg width="660" height="220">
<defs>
<linearGradient id="gradient" x1="0%" y1="0%" x2="100%" y2="0%">
<stop offset="0%" stop-color="#05a"/>
<stop offset="100%" stop-color="#0a5"/>
</linearGradient>
</defs>
<path d="M150 0 L75 200 L225 200 Z" />
</svg>

Answer 3

This type of gradient is not easy to achieve in SVG, see SVG angular gradient.
Also, transparent is not a valid color in SVG. You should state stop-opacity as in this example: http://jsfiddle.net/WF2CS/
I'm afraid the easiest solution might be a series of small arc paths with varying opacity.

Answer 4

CSS Images Module - Level 4 has introduced conic-gradient. According to MDN, it's supported in all major browsers except IE.
Although it's not, technically, a gradient along a path, since your path is a circle, the desired outcome can be achieved with:
.loader {
--size: 7.5rem;
--stroke-size: .5rem;
--diff: calc(calc(var(--size)/2) - var(--stroke-size));
background-image: conic-gradient(transparent 25%, red);
width: var(--size);
height: var(--size);
border-radius: 50%;
-webkit-mask:radial-gradient(circle var(--diff),transparent 98%,#fff 100%);
mask:radial-gradient(circle var(--diff),transparent 98%,#fff 100%);
animation: rotate 1.2s linear infinite;
margin: 0 auto;
}
#keyframes rotate {
from {
transform: rotate(0);
}
to {
transform: rotate(1turn);
}
}
body {
background: #f9fcfc url(https://picsum.photos/id/22/1323/880) 100% /cover;
margin: 0;
min-height: 100vh;
padding-top: 2.5rem;
}
* { box-sizing: border-box; }
<div class="loader"></div>
The relevant bit is
background-image: conic-gradient(transparent 25%, red);
Note: If not obvious, the CSS variables are not necessary, I just wanted a way to test it at multiple sizes without having to modify the values in more than one place.
Note: Masking the inner circle can also be achieved using an <svg />. I suspect it might have better browser support than mask. But that's outside of this question's scope.
At the time of posting, my example seems to work as expected in latest: Chrome, Firefox and Edge. Haven't tested Safari. Not expecting it to work in any version of IE.

Answer 5

I had this problem as well, so I created a library to assist in the creation of gradients that follow along a path. You can use it standalone in Javascript or alongside D3.js if you prefer. The library is 100% based off of Mike Bostock's work referenced in the first answer, but I've removed D3 as a required dependency.
I've also written a brief tutorial on Medium describing the backstory and usage..

Answer 6

Another way is to make two half circles and apply the opposite linear gradient to each's stroke, and make sure they are both contained in a g element. (In my example the combined gradient isn't 270 degrees but 360. Two half-circles are stacked vertically. The first gradient (applied to the top semi-circle's stroke) would be 100-50% opacity, then the next would have 0% to 50%. Both gradients have the unit vector set to x1,y1,y2=0 and x2=1, making them run from left to right.) Then apply transform=rotate(deg,ctrX,ctrY) to the g.

Answer 7

I managed to apply some kind of gradient following https://www.w3schools.com/graphics/svg_grad_radial.asp.
e.g.:
Codepen svg multiple path
<!DOCTYPE html>
<html>
<body>
<svg height="378" width="378" >
<defs>
<radialGradient id="grad1" cx="50%" cy="55%" r="50%">
<stop offset="90%" style="stop-color:rgb(31, 175, 198); stop-opacity: .5" />
<stop offset="100%" style="stop-color:rgb(161, 211, 60); stop-opacity: .5" />
</radialGradient>
</defs>
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<path d="M270.733 147.306C241.272 152.653 225.021 164.29 203.948 195.429C199.335 202.139 199.02 202.978 199.02 209.478C199.02 214.51 197.972 219.438 195.246 227.93C190.633 242.294 190.842 245.649 197.447 256.867C200.068 261.271 202.165 265.465 202.165 265.989C202.165 266.618 200.802 268.61 199.02 270.497C193.463 276.473 193.568 285.699 199.335 291.885C202.69 295.345 210.553 298.595 212.65 297.232C213.174 296.918 212.44 294.506 211.077 291.78C209.609 289.159 208.456 286.224 208.561 285.28C208.561 284.232 209.085 284.546 209.714 286.224C211.496 290.103 219.779 302.894 223.868 307.926C231.941 317.991 249.345 328.161 265.596 332.46C270.524 333.718 279.226 334.871 286.565 335.186C293.484 335.5 298.202 336.129 297.049 336.549C290.758 338.75 261.821 334.661 248.506 329.629L241.587 327.008L239.804 329.419C233.199 338.121 225.65 357.937 223.763 371.357L223.239 375.341H288.242C349.681 375.341 353.245 375.236 352.721 373.454C352.407 372.51 350.729 366.219 349.052 359.509C345.382 345.041 342.446 337.807 337.728 331.621C335.841 329.105 334.269 326.484 334.269 325.75C334.373 325.121 336.994 322.604 340.245 320.298C346.116 316.104 354.189 307.612 358.592 300.902C360.06 298.7 362.367 296.918 364.464 296.289C366.246 295.764 369.601 293.563 371.907 291.466C379.142 284.546 379.876 275.11 373.48 269.553C371.278 267.666 370.964 266.723 371.593 263.368C372.012 261.271 372.641 259.279 373.061 258.964C373.48 258.65 374.424 255.609 375.158 252.149C376.206 247.117 376.206 243.238 375.158 232.439C374.424 225.1 373.375 219.124 372.851 219.124C372.327 219.124 372.012 216.188 372.117 212.518C372.327 206.752 371.803 204.97 368.028 197.631C362.996 187.67 355.552 176.767 348.003 168.589C343.39 163.556 340.349 161.564 328.502 155.693C320.115 151.604 311.517 148.144 307.324 147.306C298.622 145.418 280.798 145.418 270.733 147.306Z" fill="url(#grad1)"></path>
<path d="M147.646 261.69C147.646 262.005 149.638 264.94 152.154 268.19C154.67 271.441 158.13 276.578 160.017 279.409C164.945 287.272 176.373 311.805 179.728 321.556C183.397 331.935 183.083 332.669 172.074 342C167.88 345.565 164.421 349.34 164.421 350.178C164.421 351.122 169.138 356.154 174.905 361.606C181.196 367.373 185.389 372.091 185.389 373.349C185.389 375.236 186.228 375.341 200.067 375.341C211.076 375.341 214.746 375.026 214.746 373.978C214.746 369.574 189.059 277.207 186.647 272.804C186.228 271.965 179.518 269.763 171.76 267.771C164.001 265.884 155.928 263.577 153.726 262.634C149.428 260.956 147.646 260.642 147.646 261.69Z" fill="url(#grad1)"></path>
</svg>
</body>
</html>