Raindrop FX
Optimised raindrop effect on glass with WebGL2
Inspired by https://github.com/codrops/RainEffect
Check the live demo: https://sardinefish.github.io/raindrop-fx/
Background image from https://www.pixiv.net/artworks/84765992
Usage
Use as npm package
You might need some bundle tools to run it in browser. eg. esbuild or webpack
$ npm install raindrop-fx
const RaindropFX = require("raindrop-fx");
const canvas = document.querySelector("#canvas");
const rect = canvas.getBoundingClientRect();
canvas.width = rect.width;
canvas.height = rect.height;
const raindropFx = new RaindropFX({
canvas: canvas,
background: "path/to/background/image",
});
window.onresize = () =>
{
const rect = canvas.getBoundingClientRect();
raindropFx.resize(rect.width, rect.height);
}
raindropFx.start();
In Browser
For directly use in browser, download the pre-bundled script at /bundle/index.js
and embed with your Web page.
<!DOCTYPE html>
<html lang="en">
<head>
<title>Raindrop Effect</title>
<link rel="stylesheet" href="assets/css/style.css">
<script src="./bundle/index.js"></script>
</head>
<body>
<div id="root">
<canvas id="canvas"></canvas>
</div>
<script src="./script.js"></script>
</body>
</html>
style.css
body {
margin: 0;
}
#root {
position: absolute;
width: 100vw;
height: 100vh;
}
#canvas {
width: 100%;
height: 100%;
}
script.js
const canvas = document.querySelector("#canvas");
// Set canvas size to fit the real size
const rect = canvas.getBoundingClientRect();
canvas.width = rect.width;
canvas.height = rect.height;
const raindropFx = new RaindropFX({
canvas: canvas,
background: "path/to/backgroundImage",
});
raindropFx.start();
// Resize the effect renderer
window.onresize = () =>
{
const rect = canvas.getBoundingClientRect();
raindropFx.resize(rect.width, rect.height);
}
Configuration
All options except canvas element are optional at initialize.
// Minimal startup script with a dark opacity background
const raindropFx = new RaindropFX({
canvas: canvas,
});
All options can be set dynamically by raindropFx.options.xxx=xx except renderer size and background image
Example:
// At initialize
const raindropFx = new RaindropFX({
canvas: canvas,
spawnSize = [30, 80],
spawnInterval = [0.1, 0.2],
mistBlurStep: 5,
dropletsPerSecond: 1000,
});
await raindropFx.start();
// Or set directly
raindropFx.options.spawnSize = [30, 150];
raindropFx.options.spawnInterval = [0.01, 0.05];
raindropFx.options.mistBlurStep = 5;
raindropFx.options.dropletsPerSecond = 1000;
Resize
Call raindropFx.resize to properly reszie.
raindropFx.resize(someWidth, someHeight);
Background
Background image must be set by calling to raindropFx.setBackground.
Background image source could be a url string, HTMLCanvasElement, HTMLImageElement, ArrayBuffer and other types that implemented interface TexImageSource and ArrayBufferView.
await raindropFx.setBackground("background image url");
// Set background image from HTMLImageElement
const img = new Image();
// ...
await raindropFx.setBackground(img);
// Set background image from another HTMLCanvasElement
const anotherCanvas = document.querySelector("#another-canvas");
await raindropFx.setBackground(anotherCanvas);
Raindrop Simulation Options
interface SimulationOptions
{
spawnInterval: [number, number],
/**
* Random size range when spawn a new raindrop
*/
spawnSize: [number, number],
/**
* Maximal amount of spawned raindrops.
* Recommend less than 2000
*/
spawnLimit: number,
/**
* Recommend in range (0..1), other value should be ok.
*/
slipRate: number,
/**
* Describe how often a raindrop change its motion state
*/
motionInterval: [number, number],
/**
* Random velocity x relative to velocity y.
* Recommend in range (0..0.1)
*/
xShifting: [number, number],
/**
* Relative size for collision check.
* Recommend in range (0.6..1.2)
*/
colliderSize: number,
/**
* Mass density of the slipping trail raindrop.
* Recommend in range (0.1..0.3)
*
* A large value cause a raindrop quickly lose its size during slipping.
*/
trailDropDensity: number,
/**
* Random size range of slipping trail drop.
* Recommend in range (0.3..0.5)
*/
trailDropSize: [number, number],
/**
* Random distance range between two slipping trail drop.
* Recommend in range (20..40)
*/
trailDistance: [number, number],
/**
* Vertical spread of a new spawned slipping trail drop.
* Recommend in range (0.4..0.6)
*/
trailSpread: number,
/**
* Spread rate when a new spawned raindrop hit the screen.
* Recommend in range (0.4..0.7)
*/
initialSpread: number,
/**
* Spread shrink rate per seconds.
* Recommend in range (0.01..0.02)
*/
shrinkRate: number,
/**
* Spread rate by velocity Y.
* Recommend in range (0.2..0.4)
*
* Raindrop with higher fall speed looks more narrow.
*/
velocitySpread: number,
/**
* Mass lose per second.
* Recommend in range (10..30)
*/
evaporate: number,
/**
* Gravity acceleration in pixels/s.
* Recommend 2400
*/
gravity: number,
}
Rendering Options
interface RenderingOptions
{
/**
* Background blur steps used for background & raindrop refract image.
* Value should be integer from 0 to log2(backgroundSize).
* Recommend 3 or 4
*/
backgroundBlurSteps: number,
/**
* Enable blurry mist effect
*/
mist: boolean,
/**
* [r, g, b, a] mist color, each component in range (0..1).
* The alpha is used for whole mist layer.
* Recommend [0.01, 0.01, 0.01, 1]
*/
mistColor: [number, number, number, number],
/**
* Describe how long takes mist alpha from 0 to 1
*/
mistTime: number,
/**
* Background blur steps used for mist.
* Value should be integer from 0 to log2(backgroundSize).
* Recommended value = backgroundBlurSteps + 1
*/
mistBlurStep: number,
/**
* Tiny droplet spawn rate.
*/
dropletsPerSeconds: number,
/**
* Random size range of tiny drplets.
* Recommend [10, 30]
*/
dropletSize: [number, number],
/**
* Smooth range [a, b] of raindrop edge.
* Recommend [0.96, 1.0]
*
* Larger range of (b - a) have smoother edge.
*
* Lower value b makes raindrop larger with a distort edge
*/
smoothRaindrop: [number, number],
/**
* Refract uv scale of minimal raindrop.
* Recommend in range (0.2, 0.6)
*/
refractBase: number,
/**
* Refract uv scaled by raindrop size.
* Rocommend in range (0.4, 0.8)
*/
refractScale: number,
/**
* Describe how raindrops are composed.
*
* - `smoother` compose raindrops normal with 'exclusion' blend mode
*
* - `harder` compose raindrops normal with 'normal' blend mode
*/
raindropCompose: "smoother", "harder"
/**
* Screen space (0..1) light direction or position.
* Recommend [-1, 1, 2, 0]
*
* - Use [x, y, z, 0] to indicate a direction
*
* - Use [x, y, z, 1] to indicate a position
*/
raindropLightPos: [number, number, number, number],
/**
* Lambertian diffuse lighting Color.
* Recommend [0.3, 0.3, 0.3]
*/
raindropDiffuseLight: [number, number, number],
/**
* Higher value makes more shadow.
* Recommend in range (0.6..0.8)
*/
raindropShadowOffset: number,
/**
* Similar to `smoothRaindrop`. Used to erase droplets & mist.
* Recommended value [0.93, 1.0]
*/
raindropEraserSize: [number, number],
/**
* Specular light clor.
* Recommend disable it with [0, 0, 0] :)
*/
raindropSpecularLight: [number, number, number],
/**
* Blinn-Phong exponent representing shininess.
* Value from 0 to 1024 is ok
*/
raindropSpecularShininess: number,
/**
* Will apply to calculate screen space normal for lighting.
* Larger value makes raindrops looks more flat.
* Recommend in range (0.3..1)
*/
raindropLightBump: number,
}
Performance
-
On Windows Chrome 88. It takes about 6ms to update each frame with 2000 raindrops.
-
On Android (Mi 10) Chrome 87. It takes about 6.5ms to update each frame with 2000 raindrops.
By default settins on a 1920x1080 screen, there are up to 600 raindrops on the screen, which taks 2~3ms to update each frame.