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, 3 insertions, 1 deletions

diff --git a/src/detached/wire.zig b/src/detached/wire.zig
index 3a914e42..6903a1e8 100644
--- a/src/detached/wire.zig
+++ b/src/detached/wire.zig
@@ -270,6 +270,7 @@ pub const Frame = struct {
             region.notice = try r.getByte();
             region.clip = try r.getU16();
             region.lift = @bitCast(try r.getU32());
+            region.line = @bitCast(try r.getU32());
             // A springy flavour overshoots, and a wind-up dips below.
             if (!(region.lift >= -1 and region.lift <= 2)) return error.BadValue;
             if (region.rect.x > f.cols or region.rect.w > f.cols - region.rect.x or
@@ -754,7 +755,7 @@ pub fn layersBound(layers: []const pardes.Layer, tags: []const pardes.Layer, reg
     return n + regions.len * region_len + chrome_len;
 }
 
-const region_len = 1 + 1 + 4 + 8 + 1 + 2 + 2 + 1 + 2 + 4;
+const region_len = 1 + 1 + 4 + 8 + 1 + 2 + 2 + 1 + 2 + 4 + 4;
 /// The palette: each colour three bytes, a theme's optional ones a flag
 /// before them.
 const chrome_len = @typeInfo(pardes.Chrome).@"struct".fields.len * 4 + 8 * 4;
@@ -839,6 +840,7 @@ pub fn encodeFrameLayers(out: []u8, cols: u16, rows: u16, cursor: ?Cursor, point
             try w.putByte(region.notice);
             try w.putU16(region.clip);
             try w.putU32(@bitCast(region.lift));
+            try w.putU32(@bitCast(region.line));
         }
         inline for (@typeInfo(pardes.Chrome).@"struct".fields) |field| {
             const rgb = @field(chrome, field.name);