G13: Parallax, lapis's dots drift with the text at a quarter of its speed

Parallax on|off (off, a pixel shell's; Chrome.fx bit 3). A body region
carries its first line (Region.line, a file's scroll or a terminal's grid
offset; the wire's region record grows a u32). The GUI offsets each
body's page dots by a quarter of its line in rows, and of G6's glide
offset while one runs, so the pattern drifts with the text and settles
with it; the cell shader reads it from the instance's serial slot, whose
per-cell dissolve noise G7 left unused (the dead noise code goes).

Tests: a scrolled body tells its line; the shift handed to the shader is
a quarter of it within the dots' period. Measured in a capture: four lines
move the dots 13 px (140 px / 4 mod 22). Gates as before, goldens
byte-identical. Feel review: .scratch/render/parallax/.

1 files changed, 2 insertions, 0 deletions

diff --git a/docs/config.md b/docs/config.md
index 44f37079..97bf95a1 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -578,6 +578,8 @@ HoverGlow on     a soft glow under the word a look-hover would open, fading
                  in over 80 ms
 Occlusion on     pane bodies darken faintly toward their edges (2%), never
                  over the cursor
+Parallax on      a theme's page pattern (lapis's dots) moves with the text
+                 at a quarter of its speed
 CursorBlink on   the cursor blinks, solid while typing and half a second
                  after, eased at each edge, solid after 10 idle seconds
 GripWidth 150    the grip's button and the scrollbar under it, percent of the