Add a snowfall chat effect (with /snowfall command)

src/effects/index.ts

@@ -75,6 +75,20 @@ type FireworksOptions = {
      */
     gravity: number;
 }
+type SnowfallOptions = {
+    /**
+     * The maximum number of snowflakes to render at a given time
+     */
+    maxCount: number;
+    /**
+     * The amount of gravity to apply to the snowflakes
+     */
+    gravity: number;
+    /**
+     * The amount of drift (horizontal sway) to apply to the snowflakes. Each snowflake varies.
+     */
+    maxDrift: number;
+}
 
 /**
  * This configuration defines room effects that can be triggered by custom message types and emojis
@@ -105,6 +119,18 @@ export const CHAT_EFFECTS: Array<Effect<{ [key: string]: any }>> = [
             gravity: 0.05,
         },
     } as Effect<FireworksOptions>,
+    {
+        emojis: ['❄', '🌨'],
+        msgType: 'io.element.effect.snowfall',
+        command: 'snowfall',
+        description: () => _td("Sends the given message with snowfall"),
+        fallbackMessage: () => _t("sends snowfall") + " ❄",
+        options: {
+            maxCount: 200,
+            gravity: 0.05,
+            maxDrift: 5,
+        },
+    } as Effect<SnowfallOptions>,
 ];
 
 

src/effects/snowfall/index.ts

@@ -0,0 +1,148 @@
+/*
+ Copyright 2020 The Matrix.org Foundation C.I.C.
+
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ */
+import ICanvasEffect from '../ICanvasEffect';
+import { arrayFastClone } from "../../utils/arrays";
+
+export type SnowfallOptions = {
+    /**
+     * The maximum number of snowflakes to render at a given time
+     */
+    maxCount: number;
+    /**
+     * The amount of gravity to apply to the snowflakes
+     */
+    gravity: number;
+    /**
+     * The amount of drift (horizontal sway) to apply to the snowflakes. Each snowflake varies.
+     */
+    maxDrift: number;
+}
+
+type Snowflake = {
+    x: number;
+    y: number;
+    xCol: number;
+    diameter: number;
+    maximumDrift: number;
+    gravity: number;
+}
+
+export const DefaultOptions: SnowfallOptions = {
+    maxCount: 200,
+    gravity: 0.05,
+    maxDrift: 5,
+};
+
+const KEY_FRAME_INTERVAL = 15; // 15ms, roughly
+
+export default class Snowfall implements ICanvasEffect {
+    private readonly options: SnowfallOptions;
+
+    constructor(options: { [key: string]: any }) {
+        this.options = {...DefaultOptions, ...options};
+    }
+
+    private context: CanvasRenderingContext2D | null = null;
+    private particles: Array<Snowflake> = [];
+    private lastAnimationTime: number;
+
+    public isRunning: boolean;
+
+    public start = async (canvas: HTMLCanvasElement, timeout = 3000) => {
+        if (!canvas) {
+            return;
+        }
+        this.context = canvas.getContext('2d');
+        this.particles = [];
+        const count = this.options.maxCount;
+        while (this.particles.length < count) {
+            this.particles.push(this.resetParticle({} as Snowflake, canvas.width, canvas.height));
+        }
+        this.isRunning = true;
+        requestAnimationFrame(this.renderLoop);
+        if (timeout) {
+            window.setTimeout(this.stop, timeout);
+        }
+    }
+
+    public stop = async () => {
+        this.isRunning = false;
+    }
+
+    private resetParticle = (particle: Snowflake, width: number, height: number): Snowflake => {
+        particle.x = Math.random() * width;
+        particle.y = Math.random() * -height;
+        particle.xCol = particle.x;
+        particle.diameter = (Math.random() * 7) + 4;
+        particle.maximumDrift = (Math.random() * this.options.maxDrift) + 3.5;
+        particle.gravity = this.options.gravity + (Math.random() * 6) + 4;
+        return particle;
+    }
+
+    private renderLoop = (): void => {
+        if (!this.context || !this.context.canvas) {
+            return;
+        }
+        if (this.particles.length === 0) {
+            this.context.clearRect(0, 0, this.context.canvas.width, this.context.canvas.height);
+        } else {
+            const timeDelta = Date.now() - this.lastAnimationTime;
+            if (timeDelta >= KEY_FRAME_INTERVAL || !this.lastAnimationTime) {
+                // Clear the screen first
+                this.context.clearRect(0, 0, this.context.canvas.width, this.context.canvas.height);
+
+                this.lastAnimationTime = Date.now();
+                this.animateAndRenderSnowflakes();
+            }
+            requestAnimationFrame(this.renderLoop);
+        }
+    };
+
+    private animateAndRenderSnowflakes() {
+        if (!this.context || !this.context.canvas) {
+            return;
+        }
+        const height = this.context.canvas.height;
+        for (const particle of arrayFastClone(this.particles)) {
+            particle.y += particle.gravity;
+
+            // We treat the drift as a sine function to have a more fluid-like movement instead
+            // of a pong-like movement off walls of the X column. This means that for
+            // $x=A\sin(\frac{2\pi}{P}y)$ we use the `maximumDrift` as the amplitude (A) and a
+            // large multiplier to create a very long waveform through P.
+            const peakDistance = 75 * particle.maximumDrift;
+            const PI2 = Math.PI * 2;
+            particle.x = particle.maximumDrift * Math.sin((PI2 / peakDistance) * particle.y);
+            particle.x += particle.xCol; // bring the particle to the right place
+
+            const radius = particle.diameter / 2;
+            this.context.save();
+            this.context.beginPath();
+            this.context.ellipse(particle.x, particle.y, radius, radius, 0, 0, 360);
+            this.context.fillStyle = '#eaeaea'; // grey so it shows up on the light theme
+            this.context.fill();
+            this.context.closePath();
+            this.context.restore();
+
+            // Remove any dead snowflakes
+            const maxBounds = radius * 4; // make sure it's *really* off screen
+            if (particle.y > (height + maxBounds)) {
+                const idx = this.particles.indexOf(particle);
+                this.particles.splice(idx, 1);
+            }
+        }
+    }
+}

src/i18n/strings/en_EN.json

@@ -849,6 +849,8 @@
     "sends confetti": "sends confetti",
     "Sends the given message with fireworks": "Sends the given message with fireworks",
     "sends fireworks": "sends fireworks",
+    "Sends the given message with snowfall": "Sends the given message with snowfall",
+    "sends snowfall": "sends snowfall",
     "You held the call <a>Resume</a>": "You held the call <a>Resume</a>",
     "%(peerName)s held the call": "%(peerName)s held the call",
     "Video Call": "Video Call",