302 TRON: Light Cycles game with VGA support (IEEE) :: Quicker, easier and cheaper to make your own chip!

How it works

The design implements a two-player Tron light-cycle game rendered over VGA (640×480 @ 60 Hz). The native VGA coordinates are halved to produce a virtual resolution of 320×240, which is then divided into a 32-column by 24-row grid of 10×10 pixel cells. The outer ring of cells forms the wall boundary, leaving a 30×22 playable arena.

alt text

Each player's light trail is stored as a circular buffer of up to 16 segments, where each segment holds a 5-bit column and a 5-bit row coordinate. A head pointer indexes the most recent position. On every game tick (once every 8 frames, roughly 7.5 moves per second), each player's head advances one cell in its current direction, and the oldest segment in the ring buffer is implicitly overwritten, keeping the visible trail length fixed.

Collision detection uses parallel combinational comparators across all buffer slots. Wall collisions check whether each player's next head position falls on a border cell (column 0, column 31, row 0, or row 23). Self-collisions and cross-collisions compare the next head position against all 16 slots of both trail buffers. A head-to-head collision is also detected when both players attempt to move into the same cell. Any collision triggers the game-over state.

The pixel-to-grid mapping uses a multiply-by-reciprocal technique (×205 >> 11) to divide by 10 without a hardware divider, producing the cell column and row for each pixel. Intra-cell coordinates are derived by subtracting the reconstructed cell origin. The drawing engine uses a parallel generate block to test every pixel against all trail segments at pixel rate. Each player's head cell contains a procedural directional sprite with a body region and an engine glow that rotates to face the current direction of travel. Trail segments behind the head are drawn as a narrow 2-pixel-wide light wall centered in the cell, oriented along the player's axis of movement.

Player 1 is rendered in orange/amber tones. Player 2 is rendered in cyan tones. The border uses a blue checkerboard pattern. On game over, both trails turn red until any button is pressed to restart. Direction input is latched on every clock edge with 180-degree reversal prevention (a player moving right cannot immediately switch to left, and so on). The latched direction is committed to the active direction register on each game tick.

How to test

Connect a TinyVGA to the output pins and eight active-high pushbuttons to the input pins. After reset, Player 1's light cycle starts on the left side of the arena moving right, and Player 2 starts on the right side moving left. Each player steers with four directional buttons. The trails extend behind each cycle as it moves. Crashing into any wall, either player's trail, or head-on into the other cycle triggers game over (both trails turn red). Press any button to restart.

External hardware

TinyVGA (active on output port for 640×480 VGA)
Eight momentary pushbuttons connected as follows:
- ui_in[0]: Player 1 Up
- ui_in[1]: Player 1 Down
- ui_in[2]: Player 1 Left
- ui_in[3]: Player 1 Right
- ui_in[4]: Player 2 Up
- ui_in[5]: Player 2 Down
- ui_in[6]: Player 2 Left
- ui_in[7]: Player 2 Right
VGA-compatible monitor or display

#	Input	Output
0	btn_up_1	R1
1	btn_down_1	G1
2	btn_left_1	B1
3	btn_right_1	vsync
4	btn_up_2	R0
5	btn_down_2	G0
6	btn_left_2	B0
7	btn_up_2	hsync

302 TRON: Light Cycles game with VGA support (IEEE)