The spring function is an alternative to tweened that often works better for values that are frequently changing.
In this example we have two stores — one representing the circle's coordinates, and one representing its size. Let's convert them to springs:
App.svelte
<script>
import { spring } from 'svelte/motion';
let coords = spring({ x: 50, y: 50 });
let size = spring(10);
</script>Both springs have default stiffness and damping values, which control the spring's, well... springiness. We can specify our own initial values:
App.svelte
let coords = spring({ x: 50, y: 50 }, {
stiffness: 0.1,
damping: 0.25
});Waggle your mouse around, and try dragging the sliders to get a feel for how they affect the spring's behaviour. Notice that you can adjust the values while the spring is still in motion.
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<script>
import { writable } from 'svelte/store'; let coords = writable({ x: 50, y: 50 });let size = writable(10);
</script>
<svg
on:mousemove={(e) => { coords.set({ x: e.clientX, y: e.clientY });}}
on:mousedown={() => size.set(30)} on:mouseup={() => size.set(10)}role="presentation"
>
<circle
cx={$coords.x} cy={$coords.y} r={$size}/>
</svg>
<div class="controls">
<label>
<h3>stiffness ({coords.stiffness})</h3><input
bind:value={coords.stiffness}type="range"
min="0.01"
max="1"
step="0.01"
/>
</label>
<label>
<h3>damping ({coords.damping})</h3><input
bind:value={coords.damping}type="range"
min="0.01"
max="1"
step="0.01"
/>
</label>
</div>
<style>
svg {position: absolute;
width: 100%;
height: 100%;
left: 0;
top: 0;
}
circle {fill: #ff3e00;
}
.controls {position: absolute;
top: 1em;
right: 1em;
width: 200px;
user-select: none;
}
.controls input {width: 100%;
}
</style>