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}.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/gui/Post.zig b/src/gui/Post.zig
index f715965f..45798f8d 100644
--- a/src/gui/Post.zig
+++ b/src/gui/Post.zig
@@ -98,6 +98,9 @@ ping: [2]?*c.SDL_GPUTexture = .{ null, null },
 ping_w: u32 = 0,
 ping_h: u32 = 0,
 uniforms: Uniforms = .{},
+/// The display's density, for a pass whose pattern is in logical pixels
+/// (pardesScale); the shell sets it.
+scale: f32 = 1,
 started_ns: ?u64 = null,
 last_ns: u64 = 0,
 
@@ -422,7 +425,7 @@ pub fn draw(post: *Post, device: *c.SDL_GPUDevice, cmd: *c.SDL_GPUCommandBuffer,
         const binding = c.SDL_GPUTextureSamplerBinding{ .texture = input, .sampler = sampler };
         c.SDL_BindGPUFragmentSamplers(pass_rp, 0, &binding, 1);
         c.SDL_PushGPUFragmentUniformData(cmd, 0, u, @sizeOf(Uniforms));
-        const own: [4]f32 = .{ @floatFromInt(@intFromBool(opaque_window)), @floatFromInt(pass.level), 0, 0 };
+        const own: [4]f32 = .{ @floatFromInt(@intFromBool(opaque_window)), @floatFromInt(pass.level), post.scale, 0 };
         c.SDL_PushGPUFragmentUniformData(cmd, 1, &own, @sizeOf(@TypeOf(own)));
         c.SDL_DrawGPUPrimitives(pass_rp, 3, 1, 0, 0);
         c.SDL_EndGPURenderPass(pass_rp);