512 Hardware Triangle Rasterizer with VGA Output :: Quicker, easier and cheaper to make your own chip!

512 : Hardware Triangle Rasterizer with VGA Output

Author: Pauline Zhu

Description: Edge-equation triangle rasterizer rendering filled triangles to a 256x256 VGA viewport at 640x480@60Hz

Clock: 25175000 Hz

How it works

This project implements a hardware triangle rasterizer that renders filled triangles to a VGA display at 640×480 @ 60 Hz.

The design uses the edge-equation (half-plane) method: for each edge of the triangle, a linear equation e = A·x + B·y + C is evaluated across the screen. A pixel is inside the triangle when all three edge equations are non-negative. To avoid per-pixel multiplications, the rasterizer uses incremental evaluation — edge values are updated with a single addition as the scan moves horizontally (add A) or advances a row (add B).

Pipeline

ui_in[7:0] (data_byte) + uio_in[0] (valid)
    → triangle_receiver   — collects 7 serial bytes: x0, y0, x1, y1, x2, y2, color
    → triangle_setup      — FSM computes edge coefficients A, B, C for all 3 edges
    → rasterizer          — incremental per-pixel edge evaluation, outputs pixel_on + color
    → vga_timing          — 640×480 @ 60 Hz sync generation
    → uo_out[7:0]         — VGA PMOD output

Coordinate space

Triangle vertices are specified in an 8-bit (0–255) coordinate space that maps to a centered 256×256 viewport on the 640×480 display (x offset 192, y offset 112). The surrounding area is a pink background.

Color encoding

The 8-bit color byte is packed as [7:6]=R, [5:4]=G, [3:2]=B, [1:0]=unused. Each channel has 2 bits (0–3 intensity). Example: 0xFC = white, 0x0C = blue, 0xC0 = red.

How to test

Connect a VGA monitor via the TinyTapeout VGA PMOD. To draw a triangle:

Hold rst_n low then release to reset the design.
Send 7 bytes serially through ui_in[7:0], pulsing uio_in[0] (valid) high for one clock cycle per byte:
- Byte 0: x0, Byte 1: y0
- Byte 2: x1, Byte 3: y1
- Byte 4: x2, Byte 5: y2
- Byte 6: color (0xFC = white, 0x0C = blue, 0xC0 = red)
The triangle appears within one frame (~16 ms). A new triangle can be loaded at any time after a reset.

Coordinates (0,0) = top-left of viewport; (255,255) = bottom-right.

External hardware

TinyTapeout VGA PMOD (2-bit per channel RGB, Digilent-compatible)
VGA monitor capable of 640×480 @ 60 Hz
External microcontroller or logic to send triangle bytes over ui_in / uio_in[0]

#	Input	Output	Bidirectional
0	data_byte[0]	hsync	valid (triangle data byte strobe, input)
1	data_byte[1]	blue[0]
2	data_byte[2]	green[0]
3	data_byte[3]	red[0]
4	data_byte[4]	vsync
5	data_byte[5]	blue[1]
6	data_byte[6]	green[1]
7	data_byte[7]	red[1]

Input

Output

Bidirectional

data_byte[0]

hsync

valid (triangle data byte strobe, input)

data_byte[1]

blue[0]

data_byte[2]

green[0]

data_byte[3]

red[0]

data_byte[4]

vsync

data_byte[5]

blue[1]

data_byte[6]

green[1]

data_byte[7]

red[1]

Chip location

512 Hardware Triangle Rasterizer with VGA Output