Fill the Glass

What is Fill the Glass?

Water runs from a tap at the top of the screen and falls straight past everything. Your job is to draw a line that catches it and carries it into the glass. Fill the glass to the dashed mark and the level is done. You have a limited amount of ink, shown as a bar at the top, so the line cannot simply be a giant funnel.

What makes it a puzzle rather than a doodle is that water behaves like water. It builds up behind a shallow slope, splashes off a steep one, and runs off the end of a line that stops short. A line that looks obviously right will often send half the water past the glass, and working out why is the whole game.

How to play

1. Look at where the tap is and where the glass is.
2. Draw one or more lines to guide the water across.
3. Draw as many lines as you like, then press Pour when you are ready.
4. Fill the glass to the dashed line to clear the level.
5. Undo removes your last line and gives the ink back. Start over resets everything.

How to waste less water

• Aim short of the glass, not at it. Water carries momentum along your line and keeps going. Ending the line above the middle of the glass usually overshoots the far rim.
• Shallower is better than steeper. A steep line makes the water fast, and fast water bounces and scatters. A gentle slope keeps it together.
• Add a lip at the end. A short upward kick at the bottom of your slope turns a jet into a pour, and it costs almost no ink.
• Two short lines beat one long one. You are paying for length, so a catch near the tap and a second near the glass is usually cheaper than one continuous ramp.
• Use the walls. The fixed grey walls are free. Bouncing water off one costs no ink at all.

What the physics is actually doing

The water is a few hundred small circles, each falling under gravity and colliding with your lines, the walls and the glass. What makes them behave as a liquid rather than a pile of marbles is a separation pass that pushes overlapping neighbours apart, run several times per frame so a deep pile settles rather than compressing into a lump.

Drawing them as plain circles reads as a stream of dots rather than water, so each particle is painted as a soft blob onto a lower resolution buffer and the result is thresholded. Blobs that overlap merge into one surface with a lighter skin along the top, which is what makes a pour look like a pour.

The level also does not clear the instant the water touches the mark. Splashing water can spike above the line for a single frame and then drain away, so the mark has to stay covered for about four fifths of a second before it counts. The dashed line pulses green while that is being confirmed.

That part was fiddly to get right. Pushing particles apart moves them without regard for walls, so an early version shoved the water straight through the sides of the glass and out of the world, and the glass never filled past about a fifth. The glass is now treated as a container that water cannot leave, rather than as three thin lines it can be squeezed through.

Stars, and why you might replay a level

Finishing a level is not the whole score. Every level has a par, which is the shortest route a solver could find for it. Come in within about a fifth of par and you get three stars, within about half and you get two, anything else earns one. A messy line that works still only earns one star.

That changes what the game asks of you. The first pass is about getting the water there at all. The second is about finding the shortest line that does the same job, which is a different and better puzzle. The glass keeps a face on it throughout, and it is worth watching: it starts worried and only looks pleased once you are near the mark.

Eighteen levels

Each one is built around a single idea rather than being another ramp. An open drop to start, then a shelf you have to aim off the end of, a long carry across the board, a gap to thread, a roof with one side open, a bounce that lets the wall do the work, a two stage catch, a narrow chute, a slalom, a pit, a deep well, a sloped wall you can ride most of the way, a staircase, and a last one that combines a roof, a gap and a tight budget.

Every level has been solved by a search before shipping, so par is a route that actually exists rather than a guess. If one feels impossible, it is not.

Your best level is saved in your browser. There is no timer, no lives and no way to fail permanently, so a level that goes wrong just costs you the time it takes to press Start over.