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GravityTDG

A tower defense twist: use orbital physics and rescue beams to save, rather than destroy.

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About The Game

Most tower defense games ask you to destroy whatever comes at you. Gravity TD asks you to save it. Stranded cosmonauts are drifting into the gravity well of a black hole, a dying star, an uncharted planet. You can't grab them — but you can bend the forces around them. Place jet fields to nudge their orbits, brakes to bleed off their speed, and rescue-beam turrets that charge a teleport shield before it's too late.

Built with libGDX 1.12.1, the game leverages custom RK4 (Runge-Kutta 4th Order) numerical physics at a fixed 60Hz frequency to calculate smooth planetary gravity and complex force fields. With support for sophisticated multi-touch camera gestures (pan, pitch tilt, pinch-to-zoom, and axial rotation), players can navigate space arenas seamlessly.

Core Mechanic: Every wave starts with a design phase where you spend your energy budget and study trajectory previews. Then you start the wave and watch physics do the rest — turning a death spiral into a rescue orbit!

Gallery

Key Features

RK4 Orbital Physics

High-precision 60Hz integration simulator modeling real inverse-square gravity wells, directional jet forces, and tangential drag profiles.

Tactical Phases

Plan out your approach in the paused Design Phase with real-time vector trajectory previews, then execute in the Play Phase with customizable time speeds.

Dynamic Repositioning

Brief Reposition Phase between waves allows you to relocate and optimize turrets at a reduced cost, adapting to new cosmonaut entry vectors.

Hybrid 3D/2D Visuals

Stunning 3D spheres rendered with Depth Mask buffers, mixed with screen-space overlays for additive glow coronae, Keplerian bands, and planetary Terminators.

Procedural Audio Synth

Immersive sub-bass looping drones and custom-synthesized SFX generated mathematically from Python audio engines, playing in 22kHz mono.

Star Progression

Sequentially unlocking levels with persistent high scores and star ratings based on your rescue performance saved directly to preferences.

Turret Specifications

Strategically spend your energy budget on two categories of turrets: force-field generators that steer orbits, and rescue-beam shooters that charge shields.

Turret ID	Class	Subtype	Placement Cost	Effect / Description
jet	Field	Jet Force	30 Energy	Pushes cosmonauts in the turret's facing direction. Rotate 360° in Design Phase to align forces.
brake	Field	Friction Drag	20 Energy	Applies drag directly opposing the velocity vector, slowing down fast-orbiting targets.
shooter_single	Shooter	Point Beam	40 Energy	High-strength (1.5x) rescue beam focused strictly on a single nearest cosmonaut in range.
shooter_multi	Shooter	Splash Area	60 Energy	Fills shields of all cosmonauts within range simultaneously, with a lower individual recharge rate.

Cosmonaut Reference

Different cosmonauts require tailored gravitational handling and charge speeds based on their size, speed, and shield charges.

Type	Size	Base Speed	Stickiness	Shield Cycles	Description
cosmonaut_basic	6	1.0x	1.0	1 Cycle	Standard crew member. One full charge rescues them instantly.
cosmonaut_fast	1	2.0x	14.0	1 Cycle	Tiny and fragile. Charges extremely fast, but moves at double speed through orbits.
cosmonaut_heavy	12	1.0x	0.7	3 Cycles	Massive cargo vessel. Charges slowly and must undergo 3 complete charge cycles to be rescued.

Celestial Centers & Rules

The cosmic bodies at the center of the field govern both the gravity profiles and the rules required to pull off a successful rescue:

Black Hole

Enormous gravity pull. Accompanied by Keplarian accretion disks and relativistic jets. Cosmonauts are saved immediately upon completing their shield charge anywhere in the arena.

Bright Star

Scorching corona and solar flares. Cosmonauts teleport and are saved instantly when their shield is fully charged, avoiding incineration.

Planet

Features beautiful atmospheric gradients and cloud terminators. Cosmonauts must physically land on the planet's surface after their shield has been 100% charged to be saved.

Space Station

Metallic technological outpost. Any cosmonaut that physically contacts the center station is automatically saved, regardless of their shield charge status.