Technical notebook style.

1 files changed, 37 insertions, 15 deletions

diff --git a/_log/matrix-digital-rain.md b/_log/matrix-digital-rain.md
index d3f6ab4..8512208 100644
--- a/_log/matrix-digital-rain.md
+++ b/_log/matrix-digital-rain.md
@@ -6,32 +6,54 @@ project: true
 thumbnail: thumb_sm.png
 ---
 
-Fixed the Unicode issue finally. Can now mix ASCII + Katakana.
+The 2022 version worked but had some loose ends. Unicode support was
+inflexible--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 level into the 4th byte of the RGB union - should’ve done
-this in 2022 instead of separate array. What was I thinking.
+Moved phosphor decay into the 4th byte of the RGB union--should’ve done this 
+in 2022. What was I thinking.
 
-Keeping the RGB/PD union as it is. I'm aware of the portability issues, but I’m
-on a little-endian machine, and I’m the only one reading this anyway. It’s
-cleaner.
+Keeping the RGB union despite portability concerns. All my systems are
+little-endian and the code is cleaner this way.
 
-New charset array works. UNICODE(min, max) macro packs the range into uint64.
-insert_code() unpacks block and picks random char.
+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:
 
-Full-width Katakana breaks columns. Stick to half-width (U+FF61-U+FF9F) range .
-Compile with -DNOKANA to disable Katakana altogether.
+```
+static uint64_t glyphs[] = {
+    UNICODE(0x0021, 0x007E), /* ASCII */
+    UNICODE(0xFF65, 0xFF9F), /* Half-width Katakana */
+};
+```
 
-blend() is still good, left it alone.
+Full-width Katakana breaks column alignment. Stick to half-width
+(U+FF61-U+FF9F) range. Compile with -DNOKANA to disable Katakana altogether.
 
-Tossed license and automake cruft. Just `cc -O3 main.c -o matrix`. Don't need
-the ceremony.
+blend() simulates phosphor decay by eroding RGB channels toward
+background color:
 
-Performance regressions: none. Runs like a charm on the T490. 2% CPU. No
-whirring fans.
+```
+static inline void blend(matrix *mat, size_t row, size_t col)
+{
+    unsigned char *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;
+}
+```
+
+That's still good. Leaving it alone.
+
+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:
 [03f8d87](https://git.asciimx.com/matrix-digital-rain/commit/?id=03f8d87ba7c2e46bd3f3cc4c772fb3a2ac740c92)