Make a Top-Down Shooter With Safe Projectile Hits

What you will build

Survive one twelve-enemy wave with three health and rate-limited fire.

1. Extract into a new folder and run node check.mjs from that folder.
2. For the browser games, run python3 -m http.server 8080 with Python 3 and open http://localhost:8080/index.html. Do not open modules with file://.
3. Read the full setup instructions and the original code licence. Keep your existing game on a separate test branch.

The JavaScript behaviour checks and native C comparison can run independently of the browser. Ghidra UI, physical-phone and your engine integration are separate checks. This is a small reference, not a certification of your project.

Explore the related game idea · Start with Build a Game · Improve your existing game

Five practical steps

1. Prove movement before shooting

   Choose Top-down shooter and Start. Use arrows/WASD or direction buttons. Divide the input vector by its length so diagonal movement matches horizontal speed. Clamp the player to the arena. The artwork is intentionally geometric while logic is tested.

   Expected result: Movement is equally fast in straight and diagonal directions.

   Check it: Compare one second right with one second diagonal; total distance should be approximately equal.

   stepObserve the inputs → check the state → compare the result

2. Give shots a cooldown

   Hold Shoot or Space to fire. The simulation owns the 0.22-second cooldown and each projectile position. Movement and firing use elapsed simulation time; a 120Hz display must not double the fire rate. Avoid one independent interval per projectile.

   Expected result: A bounded bullet stream moving upward.

   Check it: Hold fire for a fixed interval at two update schedules and compare the shot count.

3. Consume hits exactly once

   Mark a bullet and enemy dead when they collide. The next collision checks ignore dead objects; clean arrays after resolution. Removing array entries while iterating can skip neighbours, and a still-live bullet can wrongly kill several enemies in one frame.

   Expected result: One projectile causes one accepted hit.

   Check it: Put two enemies at the same bullet location; only one is defeated by that bullet.

4. Bound damage and the wave

   Contact starts one second of invulnerability; an escaped enemy also costs health. Twelve finite spawns lead to a win when the wave clears or a loss at zero health. The example intentionally keeps escapes separate from contact invulnerability.

   Expected result: A finite game with readable health and outcome.

   Check it: Test overlapping enemies, an escape during invulnerability, zero health and no enemies between spawn intervals.

5. Upgrade one verified system

   Add a second firing direction, one pickup or clearer hit feedback. Keep simulation decisions independent from particles. Faster projectiles can tunnel through targets; switch to swept tests or your engine physics before raising speed beyond what this fixed-step radius test can handle.

   Expected result: A playable original wave shooter and one controlled extension.

   Check it: Retest diagonal speed, pause, repeated restart, hidden-tab resume and keyboard/touch after the upgrade.

Read and reuse the actual code

shooter.mjs: complete source · Standalone behavioural checks · Shared browser runner and input. Original BINX Forge code, MIT; the package includes every required file and its notice.

export function create(){return {x:320,y:280,bullets:[],enemies:[],spawn:0,cool:0,remaining:12,kills:0,hp:3,invulnerable:0,ended:false,won:false};}
export function step(s,i,dt){
 if(s.ended)return;
 let dx=Number(!!i.right)-Number(!!i.left),dy=Number(!!i.down)-Number(!!i.up),len=Math.hypot(dx,dy)||1;
 s.x=Math.max(12,Math.min(628,s.x+dx/len*190*dt));s.y=Math.max(12,Math.min(348,s.y+dy/len*190*dt));s.cool-=dt;s.spawn-=dt;s.invulnerable=Math.max(0,s.invulnerable-dt);
 if(i.fire&&s.cool<=0){s.bullets.push({x:s.x,y:s.y,dead:false});s.cool=.22;}
 if(s.remaining>0&&s.spawn<=0){s.enemies.push({x:80+(12-s.remaining)%5*110,y:-15,dead:false});s.remaining--;s.spawn=.8;}
 for(const b of s.bullets)b.y-=360*dt;
 for(const e of s.enemies){e.y+=75*dt;for(const b of s.bullets)if(!b.dead&&!e.dead&&Math.hypot(e.x-b.x,e.y-b.y)<16){b.dead=true;e.dead=true;s.kills++;}if(!e.dead&&Math.hypot(e.x-s.x,e.y-s.y)<22){e.dead=true;if(s.invulnerable<=0){s.hp--;s.invulnerable=1;}}else if(!e.dead&&e.y>380){e.dead=true;s.hp--;}}
 s.bullets=s.bullets.filter(b=>!b.dead&&b.y>-20);s.enemies=s.enemies.filter(e=>!e.dead);
 if(s.hp<=0||(!s.remaining&&!s.enemies.length)){s.ended=true;s.won=s.hp>0;}
}

Code rights: the included MIT notice permits use, modification and distribution, including commercial games and source products, with the copyright and licence notice. Added third-party files have their own terms. Read the official licence & usage terms.

Common failures and fixes

Make Your Game Better

Change one system after the baseline works. Keep the free reference and compare the same inputs before and after.

Optional building blocks from original creators

ScreenshotFree

Godot Engine contributors · Original screenshot ↗ · CC BY 4.0 ↗. Resized and compressed.

Godot Engine contributors

Godot

Free, open-source game editor for 2D and 3D projects, with scene, animation and interface tools.

MITEngine

Official licence ↗Licensing summary, not legal advice. Check the exact edition and use.

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Creator previewFree

Kenney

UI Pack

Interface artwork for buttons, panels and sliders.

CC0-1.0Asset pack

Official licence ↗Licensing summary, not legal advice. Check the exact edition and use.

See previews & details

Inspect exact formats and editions on each resource page. Pay for a resource only when it fills an identified gap; the free code exercise needs no paid engine or pack.

Licensing summary, not legal advice. Before publishing or selling, check exact terms for finished-game use, reselling files and including files in a source/template product separately.

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