G5: lapis, 0x4200.cafe's manuscript, as a theme with its ornament

A native theme `lapis` (src/themes/lapis.zig) from web/theme/lapis.css:
a lapis-deep page, lapis tags with gold names, vellum text, vermilion
rubrics, gold rules and a vermilion tag rule, gold selection in lapis ink.
Its ornament is the theme's new `decor` (colors.Decor), drawn by a pixel
shell inside the chrome it already has (decision 1), all of it off every
focus indicator:

- page_dots: the site's gold dot grid (#e8c46a22, 22 px), drawn by the
  cell shader on page-coloured cells alone (flag 0x10000000), so it lies
  under the text and never under a selection, a tag or the cursor; fixed
  to the window, a page the panes lie on.
- rail_checker: the dither frame's gold and lapis checker in the scroll
  track (a decor kind, flag 0x08000000), anchored to its rail; the thumb
  stays solid gold.
- tag plaques (tag_border, tag_shadow, tag_stripe): every tag a raised
  plaque inside its own band, the site's trail: a 2px gold frame and a
  hard 5px vermilion shadow down and right, both within the band's rows
  and columns (down, what the slack under the text leaves), so no shadow
  reaches a body, a grip or the next pane. The focused pane's plaque is
  the code window's title bar, gold and lapis stripes of 2px, its words
  on plates of the focused ground; unfocused ones are plain; column and
  workspace tags take the object-label language (1px frame, 2px shadow
  toward the page). Drawn as decor under the cells (a group's under
  range), with blank tag cells see-through and the cells blended
  premultiplied (pipeline_over) on such frames; opaque windows only.
- title_shadow: the titles' vermilion offset shadow under a file name's
  letters, sampled in the cell shader inside the letters' own cells (flag
  0x08000000), none on a cursor.

Chrome carries the decor (decor_*, name_ink, active_name_ink); a theme
file folds a nested decor literal field by field. Left out, with why, in
docs/effects.md: the fonts, the ornaments, a decor crossfade, and in the
tty anything but the colours (a tag row has no spare cell for a shadow).
An empty column is the page. The effect id is masked to 27 bits (ui.vert/ui.frag) for the
fifth flag.

Tests: the cell flags land only on page ground and file-name cells, never
a cursor, nothing without decor; lapis's plaques stay inside their tag's
band, clear of every grip, only the focused one striped; its checker is in
the track; no other theme draws any; the separator and focus
tests cover lapis. Goldens: theme and themesel (the ring gains lapis after
acme). Gates as G4. Feel review: .scratch/render/lapis/ (lapis.png, lapis-2x.png,
tags-focused-vs-unfocused-2x.png, a PanelSlide at 60 fps and a quarter).

1 files changed, 48 insertions, 1 deletions

diff --git a/src/colors.zig b/src/colors.zig
index 4a18bba9..b44e84f9 100644
--- a/src/colors.zig
+++ b/src/colors.zig
@@ -123,6 +123,42 @@ pub fn mix(a: [3]u8, b: [3]u8) [3]u8 {
     return out;
 }
 
+/// A theme's ornament, drawn by a pixel shell inside the chrome it already
+/// has (docs/render-pipeline.md §10: no gaps between panes): the lapis
+/// theme's. Sizes are logical pixels. None of it touches a focus indicator:
+/// the dots lie on the page's own ground, the checker in the scroll track
+/// (never its thumb), a tag's plaque inside its band beside its grip (and
+/// the focused one only the more striking), and the shadow under a file
+/// name's own letters.
+pub const Decor = struct {
+    /// A dot grid on the page's ground, `page_dot_alpha` of 255 strong, a
+    /// dot one logical pixel across (fading out by a pixel and a half) every
+    /// `page_dot_px`, fixed to the window.
+    page_dots: ?[3]u8 = null,
+    page_dot_alpha: u8 = 0x22,
+    page_dot_px: u8 = 22,
+    /// A checker in the scroll track, squares of `rail_checker_px`, this
+    /// colour and the track's.
+    rail_checker: ?[3]u8 = null,
+    rail_checker_px: u8 = 3,
+    /// Every tag drawn as a raised plaque inside its own band (the site's
+    /// trail and title bars): a `tag_border` frame round the text, a hard
+    /// `tag_shadow` offset down and right by `tag_shadow_px`, both within
+    /// the band's rows and columns, never past them; the focused pane's
+    /// plaque striped `tag_stripe` and the tag's ground, `tag_stripe_px`
+    /// each, its words on plates of the ground. Column and workspace tags
+    /// take a quieter one (a one-pixel frame, a shadow of two, no stripes).
+    tag_border: ?[3]u8 = null,
+    tag_border_px: u8 = 2,
+    tag_shadow: ?[3]u8 = null,
+    tag_shadow_px: u8 = 5,
+    tag_stripe: ?[3]u8 = null,
+    tag_stripe_px: u8 = 2,
+    /// The file name's offset shadow, down and right, in a pane's tag.
+    title_shadow: ?[3]u8 = null,
+    title_shadow_px: u8 = 2,
+};
+
 pub const Theme = struct {
     name: []const u8,
     bg: ?[3]u8,
@@ -188,6 +224,8 @@ pub const Theme = struct {
     /// in pixels at a 17px tagline, the thumb one narrower (acme's 12px
     /// Scrollwid, the default).
     rail_px: ?u8 = null,
+    /// A pixel shell's ornament (Decor): lapis's.
+    decor: ?Decor = null,
 };
 
 const curated = struct {
@@ -209,6 +247,7 @@ const curated = struct {
     pub const helix = @import("themes/helix.zig");
     pub const dark = @import("themes/dark.zig");
     pub const acme = @import("themes/acme.zig");
+    pub const lapis = @import("themes/lapis.zig");
 };
 
 fn fold(comptime C: type) [@typeInfo(C).@"struct".decls.len]Theme {
@@ -219,7 +258,15 @@ fn fold(comptime C: type) [@typeInfo(C).@"struct".decls.len]Theme {
             var t: Theme = undefined;
             const source = @field(C, d.name).theme;
             for (@typeInfo(Theme).@"struct".fields) |f| {
-                @field(t, f.name) = if (@hasField(@TypeOf(source), f.name))
+                @field(t, f.name) = if (f.type == ?Decor and @hasField(@TypeOf(source), f.name)) decor: {
+                    // A nested literal is folded field by field too.
+                    var decor: Decor = .{};
+                    const given = @field(source, f.name);
+                    for (@typeInfo(Decor).@"struct".fields) |g| if (@hasField(@TypeOf(given), g.name)) {
+                        @field(decor, g.name) = @field(given, g.name);
+                    };
+                    break :decor decor;
+                } else if (@hasField(@TypeOf(source), f.name))
                     @field(source, f.name)
                 else if (f.default_value_ptr) |ptr|
                     @as(*const f.type, @ptrCast(@alignCast(ptr))).*