Building a Browser Game Where You Fly Through a Forest (It's Easier Than You Think)

A GIF started making the rounds on Reddit this week — a little bird weaving through a procedurally generated forest, all running in the browser. No Unity export. No Unreal Engine. Just the web platform doing what it does best.

I've been building small browser games as side projects for years, and every time one of these goes viral, my DMs fill up with the same question: "How hard is this to build?" Honestly? Not that hard. Let me walk you through the core pieces.

Why Browser Games Still Hit Different

There's something about clicking a link and immediately playing a game. No install, no app store, no 2GB download. The friction is basically zero, which is exactly why these things spread like wildfire on Reddit.

The modern browser is absurdly capable. Between Canvas 2D, WebGL, and now WebGPU starting to land in browsers, you can build surprisingly polished games without leaving HTML and JavaScript. The bird-in-a-forest game is a perfect example — it looks great, runs smooth, and lives in a tab.

The Core Loop: Canvas + requestAnimationFrame

Every browser game starts the same way. You grab a canvas, set up a game loop, and start drawing frames.

const canvas = document.getElementById('game');
const ctx = canvas.getContext('2d');

let lastTime = 0;

function gameLoop(timestamp) {
  const deltaTime = (timestamp - lastTime) / 1000; // seconds since last frame
  lastTime = timestamp;

  update(deltaTime);  // move stuff
  render(ctx);        // draw stuff

  requestAnimationFrame(gameLoop);
}

requestAnimationFrame(gameLoop);

That deltaTime variable is crucial. Without it, your game runs at different speeds on different machines. I learned this the hard way when my first browser game ran at warp speed on a gaming PC and at a crawl on a Chromebook.

Faking Depth: The Parallax Trick

The forest-flying effect you see in that Reddit GIF? It's almost certainly parallax scrolling. You layer multiple backgrounds moving at different speeds — trees in the foreground zip by fast, distant mountains barely crawl. Your brain fills in the depth.

const layers = [
  { trees: farTrees, speed: 0.2, y: 50 },   // distant — moves slow
  { trees: midTrees, speed: 0.6, y: 100 },   // middle ground
  { trees: nearTrees, speed: 1.0, y: 180 },  // foreground — moves fast
];

function updateLayers(deltaTime) {
  layers.forEach(layer => {
    layer.trees.forEach(tree => {
      tree.x -= layer.speed * scrollSpeed * deltaTime;

      // recycle trees that go off-screen
      if (tree.x + tree.width < 0) {
        tree.x = canvas.width + Math.random() * 200;
      }
    });
  });
}

Three layers is usually enough to sell the illusion. The recycling bit at the bottom is key — instead of generating infinite trees, you just move off-screen ones back to the right. Old trick, still works beautifully.

Procedural Tree Generation

Nobody wants to hand-draw 500 tree sprites. A simple recursive function gives you surprisingly organic-looking trees:

function drawTree(ctx, x, y, length, angle, depth) {
  if (depth === 0) {
    // draw leaves at the tips
    ctx.fillStyle = '#2d5a1e';
    ctx.beginPath();
    ctx.arc(x, y, 4, 0, Math.PI * 2);
    ctx.fill();
    return;
  }

  const endX = x + length * Math.cos(angle);
  const endY = y + length * Math.sin(angle);

  ctx.strokeStyle = depth > 2 ? '#4a3728' : '#5c7a3a';
  ctx.lineWidth = depth;  // thicker trunk, thinner branches
  ctx.beginPath();
  ctx.moveTo(x, y);
  ctx.lineTo(endX, endY);
  ctx.stroke();

  // branch out with some randomness
  const spread = 0.4 + Math.random() * 0.3;
  drawTree(ctx, endX, endY, length * 0.7, angle - spread, depth - 1);
  drawTree(ctx, endX, endY, length * 0.7, angle + spread, depth - 1);
}

// usage: trunk starts going up (negative Y is up in canvas)
drawTree(ctx, 200, canvas.height, 60, -Math.PI / 2, 6);

The Math.random() in the branch spread is what makes each tree unique. Bump the depth up to 8 or 9 and you get really dense canopies, though watch your frame budget.

The Bird: Simple Sprite Animation

For the bird itself, you don't need a complex animation system. A basic sprite sheet with 3-4 frames of wing positions and a frame timer gets you smooth flapping.

The movement should feel floaty and responsive. I usually go with a simple velocity-based approach where gravity is constantly pulling the bird down and input adds upward force. Sound familiar? Yeah, it's basically Flappy Bird physics, which is basically every side-scrolling flight game ever. The formula works.

The real magic is in the easing. Linear movement looks robotic. Add a tiny bit of lerp (linear interpolation) to the bird's vertical position and suddenly it feels alive.

Collision Detection Without Losing Your Mind

For a forest dodging game, axis-aligned bounding boxes (AABB) are more than enough. Don't reach for a physics engine unless you actually need one.

Keep your hitboxes slightly smaller than the visual sprites. Players hate feeling like they dodged something and still "died." I typically shrink hitboxes by about 20% — it feels more fair and nobody notices the leniency.

Adding Polish: The 20% That Takes 80% of the Time

• Screen shake on collision. Just offset the canvas by a few random pixels for 5-6 frames. Instant game feel.
• Particle trails behind the bird. Even 10-15 small circles fading out behind the player adds so much juice.
• Sound effects. The Web Audio API is powerful but honestly, Howler.js saves you a ton of headache with cross-browser audio.
• Progressive difficulty. Start the scroll speed slow and ramp it up. Players feel like they're improving even when the game is just getting harder.

Shipping It: From Localhost to Shareable

Here's where a lot of devs stall. The game works locally but then you want a leaderboard, maybe user accounts so people can save high scores. Suddenly you're building auth flows instead of finishing your game.

My advice: keep it simple. For a leaderboard, a serverless function plus a database is enough. If you do want user accounts, tools like Authon, Clerk, and Auth0 handle the auth plumbing so you can stay focused on gameplay. Don't build login flows from scratch for a side project — I've made that mistake twice.

For hosting, literally any static host works. Netlify, Vercel, even GitHub Pages. Your entire game is client-side JavaScript. Deploy it, share the link on Reddit, and watch the traffic spike.

Go Build Something

The bird-in-a-forest game that hit Reddit's front page isn't using any secret technology. It's Canvas API, some clever layering, and good game feel. The barrier to building browser games has never been lower.

Start with the game loop. Add a moving rectangle. Replace it with a bird. Add trees. Add collision. Add polish. Ship it.

The whole thing can be a single HTML file if you want. No build step, no bundler, no framework. Just open a text editor and start drawing pixels. That's the beauty of the web platform — it's always been a game engine, most of us just forgot.