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---
title: 'Matrix Rain: 2025 refactor'
date: 2025-12-21
layout: post
project: true
thumbnail: thumb_sm.png
---
The 2022 version worked but had some loose ends. Unicode support was
incomplete--couldn't mix ASCII with Katakana; Phosphor decay was stored in a
separate array when it should've been packed with RGB; Code was harder to read
than it needed to be.
<video style="max-width:100%;" controls="" poster="poster.png">
<source src="matrix.mp4" type="video/mp4">
</video>
Moved phosphor decay into the 4th byte of the RGB union--should’ve done this
in 2022; What was I thinking.
Keeping the RGB union despite portability concerns. All my systems are
little-endian and the code is cleaner this way.
Fixed Unicode by introducing a charset array. UNICODE(min, max) packs Unicode
ranges into uint64: low four bytes for start, high four bytes for end.
insert_code() unpacks a random block and picks a character from it:
```
#define UNICODE(min, max) (((uint64_t)max << 32) | min)
static uint64_t glyphs[] = {
UNICODE(0x0021, 0x007E), /* ASCII */
UNICODE(0xFF65, 0xFF9F), /* Half-width Katakana */
};
static inline void insert_code(matrix *mat,
size_t row, size_t col)
{
uint64_t blk;
uint32_t min, max;
blk = glyphs[(xor() % glyphlen)];
min = (uint32_t)blk;
max = (uint32_t)(blk >> 32);
mat->code[index(mat, row, col)] = xor() % (max - min) + min;
}
```
Full-width Katakana breaks column alignment. Stick to half-width
(U+FF61-U+FF9F) range. Compile with -DNOKANA to disable Katakana altogether.
blend() for screen decay is still good:
```
static inline void blend(matrix *mat,
size_t row, size_t col)
{
unsigned char *color;
color = mat->rgb[index(mat, row, col)].color;
color[R] = color[R] - (color[R] - RGB_BG_RED) / DECAY_MPLIER;
color[G] = color[G] - (color[G] - RGB_BG_GRN) / DECAY_MPLIER;
color[B] = color[B] - (color[B] - RGB_BG_BLU) / DECAY_MPLIER;
}
```
Left it alone.
Optimized RNG--xorshift instead of rand():
```
static inline uint32_t xor(void)
{
/* Xorshift RNGs, George Marsaglia, Florida State University. */
static uint32_t y = 2463534242;
y ^= (y << 13);
y = (y >> 17);
return (y ^= (y << 5));
}
```
NOTE: Non-linear variations (xorshitr+) for more speed.
Tossed license and automake cruft. Just `cc -O3 main.c -o matrix` now. Don't
need the ceremony.
Runs at 2-3% CPU on OpenBSD (T490). No regressions. Fans are quiet.
Commit: <a
href="https://git.asciimx.com/matrix-digital-rain/commit/?id=f71b0de15a94d21ea60d281d73fa41311d8e5197"
class="external" target="_blank" rel="noopener noreferrer">f71b0de</a>.
|
