You pick a material from the strip on the left, draw with it on the canvas and the simulation does the rest. Sand falls, piles up and rolls down its own slope until the heap sits at an angle of repose of roughly thirty-four degrees. Water falls, finds its way sideways and levels out. Oil keeps floating on top and sand sinks through it, because every material has a density taken from an ordinary reference book. Smoke and steam rise and mix with the air. Stone, wood, brick and steel stay where you put them until they melt or catch fire. There is no start screen: the canvas is already running when the page opens, with a trickle of sand, a tank of water and a small fire on a plank. Pause, single step and undo are in the bar at the top.
Every cell carries a temperature in kelvin, even an empty one. Heat flows from cell to cell with a conductivity per material: iron fast, wood slowly, air hardly at all. Put lava next to water and the water boils into steam while the lava solidifies into stone. Ice melts at zero degrees back into the water it came from, and salt water that freezes remembers that it was salty. Sand melts at well over seventeen hundred degrees into molten glass and solidifies into glass. Fire ignites wood, planks, oil and plants with a chance that differs per material, heats the air above it and goes out when it touches water. With the heating and cooling brushes you adjust the temperature of part of the world yourself, and with the pressure brush you give the air a push: the airflow that follows blows sand, water and smoke away.
This version counts 124 materials in eight groups. Powders: sand, soil, clay, gravel, salt, sugar, flour, snow, ash, soot, charcoal, quicklime, cement, sulphur, saltpetre, iron filings and glass powder. Flammable and explosive: gunpowder, thermite, magnesium and aluminium powder, dynamite, TNT, nitroglycerine, plastic explosive, napalm, fuse, fast fuse, detonator cap, firework star, cold fire and phosphorus. Liquids: water, salt water, sparkling water, oil, petrol, diesel, alcohol, acetone, honey, mercury, acid, lye, paint, tar, liquid nitrogen, lava, molten glass and molten metal. Gases: steam, smoke, vapour, fog, hydrogen, oxygen, nitrogen, helium, carbon dioxide, methane, propane, chlorine, ammonia, compressed air and vacuum. Building materials: stone, granite, sandstone, limestone, brick, concrete, reinforced concrete, asphalt, wood, plank, chipboard, paper, cardboard, cloth, rope, straw, cork, polystyrene foam, rubber, plastic, wax, ceramic, insulation wool, glass, toughened glass and coal. Metals: iron, steel, stainless steel, copper, aluminium, lead, gold, silver, titanium, tungsten, diamond, graphite, silicon, sodium and a magnet. Heat and cold: fire, gas flame, plasma, glowing coal, a heat source, a cold source, a thermostat, ice, frost, lightning and dry ice. And the beginning of nuclear and radiation: uranium, enriched uranium, plutonium, a fuel rod and radioactive waste, which warm up by themselves. On top of that there are seven materials you cannot pick but can make, such as rust, embers, slaked lime and glass shards. Every material is one row in a table: density, melting and boiling point, flammability, how hot it burns and what it leaves behind, resistance to acid, what it emits. The reactions between neighbours are in a separate list: salt dissolves in water, acid eats metal and releases hydrogen, lye neutralises acid, sodium explodes in water, limestone fizzes in acid, cement becomes concrete, acetone dissolves polystyrene, iron rusts in salt water. Explosives go off from heat or a pressure blast and really push matter away through the air; thermite burns its way through steel; a flour cloud explodes where a flour pile only burns on the outside. What is deliberately not in yet: electronics, neutrons and photons (and thus nuclear fission as a chain reaction, mirrors and radiation shields), the game of life and machines such as pistons, pipes and sources. Those follow in the last steps, together with the example maps.
The canvas is a grid of cells that is computed sixty times per second, in a fixed step that is independent of your screen's refresh rate. The grid size is measured when the page opens rather than guessed: the page briefly runs a fixed test scene and picks the largest size this device can run smoothly. If it gets too heavy along the way, the pace drops to thirty steps per second and then the world goes one size smaller; that is shown in the small readout at the top right. Everything is computed in your own browser and nothing is sent to a server. The model is a game, not a laboratory: gravity is one cell per step, heat flows pairwise between neighbours and the air is a coarse grid of pressure and velocity. This genre is called falling sand; better-known examples of it exist. This is our own build, not a copy or port of anyone else's program.
With Ctrl+S (or the button with the down arrow) you save your world as a small file with the extension .dlz; with Ctrl+O, the folder button or by dragging the file onto the canvas you open it again. The file holds the materials, the temperature of every cell, the walls, the pressure and the wind, and it is compressed in your browser: a calm world is a few tens of kilobytes, a world full of noise after an explosion considerably more. If the world is small enough, you share it with the link button: the whole world is then inside the web address and still nothing goes to a server; if it is too large for a link, you get the same file as a download and the screen says so. A file is checked completely before it replaces your world. If the size is wrong, it contains a material this tool does not know, a temperature is nonsensical or the file ends halfway, your world stays as it is and the screen says why.
The tools are on the left. The brush draws round, square, as a line or as a rectangle, with the size on the slider or with [ and ]; fill fills an enclosed area or replaces a connected material; the eraser removes material, wall and colour; the pipette picks up the material under the pointer; decoration gives cells a colour that travels with the cell; heat and cool adjust the temperature; pressure blast and suction give the air a push; wind makes it blow in the direction you drag; the stamp copies a cut-out and places it elsewhere with a click; and properties shows the material, temperature, pressure, wind and lifetime of the cell under the pointer. Walls come in eight kinds: a solid wall, gas only, liquid only, powder only, heat-conducting, insulating, and portal in and portal out — whatever falls into the entrance comes out of the exit. You pick materials in three layers: a row with the eight you used last, the groups as tabs, and below them the materials of the chosen group. The / key searches by name, and whoever points at a material or presses it for a moment gets the material card: density, melting and boiling point, flammability and the materials it reacts with. Undo (Ctrl+Z) remembers one step per stroke, up to forty steps or forty-eight megabytes; redo is Ctrl+Y. Also: pause, one step forward, the speed from a quarter to four times, and five views with the keys 1 to 5: normal, heat, pressure, velocity and fire. Every key works without first clicking the canvas, except while you type in an input field.