Week 2: A game that needs a screen cannot be measured

If a game's rules cannot run without its renderer, nothing about it can be measured. This week the specimen runs with no window open, in 6 ms.

2 March 2027

Is it me or is it the game? You cannot tell by playing alone. In the two minutes a person spends on one run, the rules on their own get through about twenty thousand.

Open the slides

A person needs 120 s to play one run of Close Quarters. The rules need about 6 ms. Everything else in this course is built on that gap.

The claim#

You cannot measure a game whose rules are tangled up with its drawing code. A run that needs a window, a frame clock and a person holding the keys happens once every two minutes. A run that needs none of them happens about twenty thousand times in the same two minutes.

What makes the specimen measurable#

All of Close Quarters lives in one function:

step(run, dt, input, rng)

It takes the state of a run, a slice of time, a direction and a source of random numbers, and it moves the run forward. There is no canvas in it and no clock. Three things follow.

• Time is handed in. A run is 7200 steps of 1/60 s. Nothing waits for a real second to pass.
• Randomness is handed in. The same seed gives the same run. Seed 97 ends at 69.333 s with 58 kills, every time you run it on the same kind of machine. That last clause is a real limit. Math.sin and its neighbours are not rounded the same way everywhere. Node on the Apple laptop these numbers were measured on ends seed 97 at 69.333 s; Node on the Linux server that checks this course’s code ends it at 63.1 s; Chrome on the same laptop turns the 50 ms player’s 38 wins into 37. The seed fixes the dice. It does not fix the arithmetic.
• The player is handed in. input is a direction. It does not care whether a hand or a function produced it. Week three is about that function.

What you leave with#

One run of the specimen on your own machine, with no window open: how long it took in milliseconds, how it ended, and proof that the same seed ends the same way twice.