Rules and chrome scale with the display's density; dark pages get visible separators and focus tints

Density: dp() in gui.zig draws every size given in pixels in logical
pixels (SDL's window display scale, rounded, at least one), as acme scales
Border, ButtonBorder and Scrollgap: the rules (rule_px), the tag rule, the
grip's ring, its dirty gap and mode bars, the rail's gap to the text and
its minimum, the thumb's inset, the rim, a bar cursor's minimum width,
underline and strikethrough thickness (the atlas is dropped on a scale
change), the rule-grab margin, and the Crt's scanline and mask periods
(pardesScale in the post prefix). Cell- and tagline-measured sizes stay:
the rail's width, Lift's blur and offsets, every motion; iResolution,
fragCoord and iMouse stay in the display's pixels, as ghostty's.
PARDES_TEST_SCALE forces a density in a harness (a test window is 1x
otherwise, whatever display it lands on) and sizes the test font with it.

Colours: a separator that stands off its page by less than 1.5:1 is lifted
toward the text to 1.6:1 (helix, atelier, paper; a theme with no page,
dark, is judged against #121212), and empty_col follows it. forge's own
rule already stands at 3.83:1; what hid it was density: 2 device pixels
on a 3x screen, now 6 (dp). A focused tag's tint closer than 1.5:1 to the
plain tag on a dark page (1.25:1 on a light one) is pushed further the way
it leans, as far as its text keeps its own contrast or 4.5: forge
1.23 -> 1.51 (#2d3440 -> #374253), and likewise dusk, orchard, ink,
lagoon, clay, harvest, spectrum, solarium, forge_soft; daybreak, atelier,
paper to 1.25. dark and helix gain a tint of their own (dark: #484566
under #c8c8c8, 1.54:1; helix: ramp 237 under 250, 1.65:1).

Tag caret: past a full row's end, the G3 glide box sits on the tag's right
edge, where the layer's caret and the pixel shell's are.

Tests: every native theme's separator >= 1.5 and every dark one has a
tint >= 1.25 with readable text; forge keeps its own border; the tag caret
glide box at a full row; at 2x the spine, tag rule, ring, rail start and
gap, and bar cursor double. Legacy-ThemeFile test strips helix's new pair.

Goldens: snapshot goldens change in colour rows only, the tints (orchard
#283a2f -> #314738 at boot, forge, helix and dark in theme/themesel).
GUI goldens: the harness's single Del of the renamed wide pane is refused
since ysqnkyoy (a rename counted as unsaved; fixed on the 9P line in
wkzlsqvy), so scenes 09-17 were recorded with that pane open and the file
was stale since the merge (08 and 18 also moved with ykvnltvs's full-row
tag wrap). The goldens here were recorded with that pane closed (as
wkzlsqvy will close it); against the parent's binary under the same
conditions they differ only in the tints: 01-13 forge's (#2d3440 ->
#374253, and the glyph edges on it), 14 ink's; 15-18 are byte-identical.
Until wkzlsqvy is merged, a run here fails 09-17. Each commit reproduces its own
recorded goldens on this machine (checked at kvtmqkyn). A test window is
1x unless PARDES_TEST_SCALE says otherwise, whatever display it opens on.
Prebuilt shaders refreshed from their sources.
Captures: .scratch/render/dark-borders/{before,after,compare,scale2,scale3}.

2 files changed, 9 insertions, 3 deletions

diff --git a/shaders/post/crt.glsl b/shaders/post/crt.glsl
index 768157ef..970d61ee 100644
--- a/shaders/post/crt.glsl
+++ b/shaders/post/crt.glsl
@@ -69,9 +69,11 @@ void mainImage(out vec4 fragColor, in vec2 fragCoord) {
     // A beam is brightest on its line and falls off between lines; the
     // mask is three phosphor stripes a triad. Both average to one, so the
     // theme keeps its brightness.
-    float line = 0.5 + 0.5 * cos(fragCoord.y * TAU / SCAN_PERIOD_PX);
+    // Periods in logical pixels: the same look at any density.
+    float density = max(1.0, pardesScale);
+    float line = 0.5 + 0.5 * cos(fragCoord.y * TAU / (SCAN_PERIOD_PX * density));
     col *= 1.0 - scanStrength() * (line * line - 0.375) / 0.625;
-    col *= 1.0 + maskStrength() * cos(fragCoord.x * TAU / MASK_PERIOD_PX + vec3(0.0, TAU / 3.0, 2.0 * TAU / 3.0));
+    col *= 1.0 + maskStrength() * cos(fragCoord.x * TAU / (MASK_PERIOD_PX * density) + vec3(0.0, TAU / 3.0, 2.0 * TAU / 3.0));
 
     float vignette = 1.0 - vignetteStrength() * pow(clamp(r2 * 0.5, 0.0, 1.0), 1.6);
     float hum = 1.0 + humStrength() * sin((uv.y * 1.35 - iTime * HUM_HZ) * TAU);
diff --git a/shaders/post/prefix.glsl b/shaders/post/prefix.glsl
index e718a98f..7a50936e 100644
--- a/shaders/post/prefix.glsl
+++ b/shaders/post/prefix.glsl
@@ -41,10 +41,14 @@ layout(set = 3, binding = 0, std140) uniform Globals {
 
 // pardes's own: pardesOpaque is 1 when the window is opaque, so a pass
 // cannot punch holes in it through its alpha; pardesLevel is a bundled
-// pass's strength, 1 to 3 (`Crt 3`), and 0 for a user's file.
+// pass's strength, 1 to 3 (`Crt 3`), and 0 for a user's file; pardesScale
+// is the display's density (2 on a 2x screen), for a pass whose pattern is
+// in logical pixels. iResolution, fragCoord and iMouse stay in the display's
+// pixels, as ghostty's do.
 layout(set = 3, binding = 1, std140) uniform PardesPost {
     float pardesOpaque;
     float pardesLevel;
+    float pardesScale;
 };
 
 // A bundled pass's constant at levels 1, 2 and 3.