Wormy is a very simple, addictive last person video game. This last person, open-world game takes you down the path of an earthworm. Wormy’s world is made up of a 4x4 grid represented by 3x16-bit arrays: Direction, Direction, and Occupied. The Direction[x] maps keep track of which way a segment of worm moves, if it is on, and Occupied keeps track of if the grid location is occupied.
Example Occupied Grid:
_________ | X X X X | | X | | X | |_________|
In addition to direction and occupied there are also pointers to the head and the tail. The same grid would look something like the following:
Example Occupied Grid with head(H) and tail(T) highlighted:
_________ | T X X X | | X | | H | |_________|
BOOM! Wormy shouldn’t run into itself. If its head hits any part of its body, that causes a collision. There is a collision if the location of the Wormy’s head is occupied by another segment of the Wormy. To determine this, we keep track of the worm location, and specifically the current and future locations of the worm head (H) and tail (T). If the future location of H will occupy a location that will already be occupied, this causes a collision.
This is made a bit trickier with growth (see below), because if the future state of H is set to occupy the current state of T - there is only a collision if growth is set to occur in the next cycle, so be careful if you plan to have Wormy chase its tail! SPLAT!
NOM NOM! Wormy eats the tasty earth around it and grows. Every so often Wormy, after having eaten all of its lunch, grows a whole segment. During a growth cycle, the state of T simply persists (remains occupied and heading in the same direction as it is).
Last Person Input - see user_input.v To move Wormy along, the last player needs to push buttons to help Wormy find more tasty earth: up, right, down or left.
Buttons are nasty little bugs in general. When pushed the button generates an analog signal that might not look exactly like a single rising edge.
It might look something like this:
xxxxxxxxxxxxxxxxx xx x x x x x x x x x x x xx x x x xxxx x x x xx x x x x x x x x x xx x x x xxx x x x x xx x x x x x x x x x x x xx x x xx x x xxxxxxxxxxxxxxxxxxx x
In order to help protect our logic from this scary looking signal that might introduce metastability (<- WHAT?), we can filter it with a couple flippy-floppies and keep the metastability at bay. ARGH.
Once we have a clear pushed or not-pushed, we can suggest that Wormy move in a specific direction. If the last player tries button mashing, Wormy won’t listen. Once a second Wormy checks what the last button press was and tries really hard to go that way (see BOOM!).
Earthworms don’t have eyes - see multiplexer.v The game’s display is made up of a 4x4 grid of LEDs controlled by a multiplexer. Why multiplexing? With a multiplexed LED setup, we can control more display units (LEDs), with a limited number of outputs (8 on this TinyTapeout project).
To get multiplexing working the network of outputs is mapped to each display unit. This allows us to manipulate assigned outputs to control the state of each display unit, one at a time. We then cycle through each display unit quickly enough to display a persistent image to the last player.
Wires (A1-4, B1-4) map to each location on the game arena (4x4 grid):
A1| | | | __________________ A2| | | | __________________ A3| | | | __________________ A4| | | | __________________ |B1 |B2 |B3 |B4
When B’s voltage is OFF the LED’s state changes to ON if A is also ON.
Example: The 3 filled squares below each represent a Wormy segment in the ON state as controlled by the multiplexer. Notice how each is lighter than the last. This is because the multiplexer cycles through each LED to update the state, creating one persistent image even though the LEDS are not on over the entire period of time.
A1| | O | | __________________ A2| | o | | __________________ A3| | . | | __________________ A4| | | | __________________ |B1 |B2 |B3 |B4
Another Example: If you enter a dark cave and point a flashlight straight ahead at one point on the wall you have a very small visual field that is contained within the beam of light. However, you can expand your visual field in the cave by waving the flashlight back and forth across the wall. Despite the fact that the beam is moving over individual points on the wall, the entire wall can be seen at once. This is similar to the concept used in the Wormy display, since the multiplexer changes the state of the worm occupied locations to ON one at a time, but in a cycle. The result is a solid image, made up of LEDs cycling through ON states to produce a persistent image of Wormy (that beautiful Lumbricina).
After reset, you should see a single pixel moving along the display and it should grow every now and then.
|0||clock||A0 - Multiplexer channel A to be tied to a an array of 16 multiplexed LEDs|
|4||button2||B0 - Multiplexer channel B to be tied to a an array of 16 multiplexed LEDs|