Fallen SandIn developmentv0.1.0

A post-apocalyptic falling-sand shooter. Every pixel of the world is simulated: walls crumble, sewage flows, methane pockets explode, and a building that loses its support comes down. You descend from the ruined street, through the buildings and the sewers, toward whatever is underneath.

A ruined street between two apartment buildings, in a low-resolution pixel style — The street. Two terraces of buildings with basements under them, a sewer under the road, caves in the yards behind.

What it is

The world is a grid of cells, and each cell is a material with its own rules. Powders fall and pile. Liquids spread and layer by density. Gases rise and drift. Fire catches on wood, oil and gasoline, boils water into steam and dies into smoke. Solids need holding up: a slab is held by its walls, a cantilever only so far, and what is cut off by a blast or dug out from under comes away a moment later.

You carry up to three guns and a throwable. Rounds carve what they can pass through and chip what stops them. Guns are built from parts, and parts have a quality, rusty to mint. Things lie about the block in caches and fall from the raiders you kill: rounds, parts, bombs, meds and scrap. Every building has a beacon on its top floor; starting a holdout brings three waves of the horde up the stairs, and the room's cache opens when the last is held.

The look is deliberately low: a 480 by 270 internal resolution scaled up in whole pixels, a muted palette, film grain, darkness and flashlight cones.

Pillars

Every pixel is simulated.
Guns carve the world.
Structures collapse when they lose support.
Scavenge and survive on the way down.
Gritty, low-res, washed out.
Deterministic, so co-op and replays can follow.

Ways to play

Story: The descent and its objective: a radio, a relay mast on a roof, the raider boss's access card, a vault door in the sewers and the Shelter beneath the city.
Survival: Everything on and no end. Scored by time survived, depth, kills and holdouts held.
Creative: The city with nobody home and everything to hand. Spawn keys and a free camera.
Endless waves: A walled arena, a breather before every wave, waves that grow, a boss every fifth. Scored by the wave reached.
Daily challenge: Survival or waves on a seed from the date, the same for everyone. One counted attempt a day.
Co-op: One machine hosts a lobby and picks the mode, difficulty and seed. Others join by address. Names over heads and in the summary.

What the world does

Fire spreads through wood, gasoline, oil, methane and gunpowder. Water puts it out.
Heat moves between touching things, rises through the air, boils water and freezes it.
Chemistry: sieves, dissolving, acids and bases, gunpowder from the ground up, a journal of discoveries.
Metallurgy: lead, aluminium, copper and steel that melt and set, molds, castings with a quality read from the pour.
Machines: pressure plates, timers, relays, an auto-turret, tripwires, spike traps, floodlights, a still and a forge bench.
The wasteland: radiation from fallout and waste, fallout storms with a minute's warning, a geiger counter, a gas mask and a hazmat suit.
The body: wounds bleed until they clot or are bandaged, sewage on the skin sickens, a long fall hurts.
Loot, inventory, gun parts and rounds of different kinds: hollow points, armour piercing, incendiaries, slugs.

Screens

Cutaway of two apartment buildings with a crater between them — Buildings are cut open as you fight through them. Every wall is cells.

A flooded sewer tunnel under the street — The sewer under the street. Sewage flows, methane pools under the ceiling.

A holdout on a top floor, lit red, with a wave counter — A holdout: three waves come up the stairs for you.

A survivor at the start of a run, flashlight cone cutting through the dust — The start of a run. Darkness and a flashlight cone.

A co-op session seen from the second player, with a downed-player notice — Co-op, seen from the second player. One machine hosts, the others join by address.

The death screen summarising a run — The death screen says what killed you and how the run went.

Under the hood

Native C++20 on SDL3 and its GPU API, with shaders in HLSL cross-compiled per platform. The cell simulation runs on the CPU in 64 by 64 chunks, four passes a tick in a checkerboard so chunks can be updated in parallel without racing. It steps at a fixed 60 Hz with a seeded RNG, so a world simulates the same on any machine. Tests run a seeded world and hash the result. Collapsing structures become rigid bodies in Box2D. Rendering, lighting and post-processing (palette LUT, grain, dither, vignette) are on the GPU.

C++20
SDL3
SDL_GPU
HLSL
Box2D
EnTT
enkiTS
Tracy
CMake
vcpkg

Fallen Sand 3D

A companion project started in October 2026: the same game in three dimensions, with the cell simulation moved to the GPU. A city block of 256 cubed cells, a surface meshed from the voxels instead of blocky cubes, the same short draw distance and low resolution. Tunnels collapse unless shored up, a flooded room drains through the hole you shot in its floor, gas pools under ceilings, fire climbs stairwells.

Early. The 2D game is the one that is playable today.

Release

Fallen Sand is built for Windows and is not released yet. A Steam release is being considered; there is no store page. Progress shows up on the blog when there is something worth writing about.