fix: step text cursors by advance, not ink width

The date rendered as "16 /SEP /2026", each slash jammed against the
next glyph. measure() returns the ink width, which ignores leading and
trailing spaces because a space carries no ink, and clock.lua was using
it to advance a cursor. Measured: " / " covers 6px of ink but advances
14px, so every separator lost 8px.

Splits the two uses that were conflated in one function. measure() is
for centring and right-aligning, where ink width is what you want;
advance() returns x_advance and is for laying out runs of text left to
right. The clock's date now uses advance() and reads "16 / SEP / 2026"
with even gaps, verified by screenshot.

Worth the split rather than changing measure() in place: text_right is
a correct caller of the ink width, so one function cannot serve both
and silently returning the advance would have broken alignment
instead.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/lib/card.lua b/lib/card.lua
index 474228d..4d94465 100644
--- a/lib/card.lua
+++ b/lib/card.lua
@@ -44,11 +44,26 @@ end
 -- values before the next call overwrites them.
 local extents = cairo_text_extents_t:create()
 
+-- Ink size of a string: how much space the glyphs actually cover.
+-- Use this to CENTRE or RIGHT-ALIGN text, never to advance a cursor.
 function M.measure(cr, s)
   cairo_text_extents(cr, s, extents)
   return extents.width, extents.height
 end
 
+-- How far the cursor moves after drawing a string. Use this to lay out runs of
+-- text left to right.
+--
+-- Not measure(): that returns the INK width, which ignores leading and
+-- trailing spaces because a space carries no ink. Stepping a cursor by the ink
+-- width collapses the gaps, and " / " measures 6px of ink against a 14px
+-- advance, so a date drawn in segments came out as "16 /SEP /2026" with each
+-- slash jammed into the next glyph.
+function M.advance(cr, s)
+  cairo_text_extents(cr, s, extents)
+  return extents.x_advance
+end
+
 -- Right-aligned text: x is the RIGHT edge.
 function M.text_right(cr, x, y, s)
   local w = M.measure(cr, s)