Lift takes a style: shadow, surface, rim, glow or auto

The user wants Lift to read on dark themes, where a shadow has nothing to
darken. `Lift shadow|surface|rim|glow|auto` (`on` is auto, bare flips
auto and off): surface lightens the lifted part's ground about 5.5%
(Material-dark), rim is a thin soft light off its top and left edges,
glow a faint halo in the theme's accent (Chrome.accent, the focused box
colour), auto a shadow on a light page and surface with half a rim on a
dark one (by the page's luminance). Rim and glow are the soft kernel in a
light colour (no pre-warp: coloured light is laid on as is, within §8.2's
budget); each style is capped per theme so text keeps min(its contrast,
4.5) (tests: darkening and lightening over the native themes). The style
travels in the palette (Chrome.lift_style, one byte on the wire). Config
reports and ctl reads `Lift <style>`.

Shared files touched: config.zig, builtins.zig, ninep/ctl.zig,
detached/wire.zig (palette byte), gui.zig. Not touched: pardes.zig,
Messages.zig, mouse.zig.

1 files changed, 4 insertions, 2 deletions

diff --git a/shaders/decor.frag.glsl b/shaders/decor.frag.glsl
index 77f9c95e..3e2c286f 100644
--- a/shaders/decor.frag.glsl
+++ b/shaders/decor.frag.glsl
@@ -8,7 +8,7 @@
 // colour rides in the cell's ground (a_bg), its coverage in a_fg.r, so the
 // result is the overlay pipeline's exactly.
 //
-// Soft shadow (flag 0x10000000): a rectangle's shadow blurred by a Gaussian,
+// Soft (flag 0x10000000): a rectangle's shadow, rim or glow blurred by a Gaussian,
 // in closed form (the product of two erf edges), on one quad grown by 3
 // sigma: no blur pass. Everything is in the quad's own 0..1 space, so a
 // track's transform carries it: sigma per axis in the uv, the caster's
@@ -62,7 +62,9 @@ void main() {
     vec2 caster1 = 1.0 - m - v_fg.gb;
     if (all(greaterThanEqual(p, caster0)) && all(lessThan(p, caster1))) discard;
     float a = v_fg.r * edge(p.x, m.x, 1.0 - m.x, s.x) * edge(p.y, m.y, 1.0 - m.y, s.y);
-    a = 1.0 - pow(max(1.0 - a, 0.0), 1.0 / 2.2);
+    // Black darkens in linear light; a light colour (a rim, a glow) is laid
+    // on as it is, within §8.2's 25%.
+    if (all(equal(v_bg, vec3(0.0)))) a = 1.0 - pow(max(1.0 - a, 0.0), 1.0 / 2.2);
     a = clamp(a + (ign(gl_FragCoord.xy) - 0.5) / 255.0, 0.0, 1.0);
     o_col = vec4(v_bg * opacity, a);
 }