fix(card): draw emoji in Noto Emoji instead of tofuHEADmaster

Cairo's toy text API binds one face with no per-glyph fallback, so an
emoji in a calendar event title rendered as a box in Noto Sans.
text/measure/advance now split strings into runs and draw emoji runs
(U+1F000-1FAFF, U+2600-27BF) in monochrome Noto Emoji, restoring the
caller's face afterwards. Nerd Font PUA icons stay in FONT_MONO.
Plain strings and invalid UTF-8 take the old single-call path.

No shaping: ZWJ sequences and flags draw as their parts. Pango via
lgi (built for Lua 5.4) is the upgrade path.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2 files changed, 114 insertions, 7 deletions

diff --git a/lib/card.lua b/lib/card.lua
index dde4121..7fd40f8 100644
--- a/lib/card.lua
+++ b/lib/card.lua
@@ -27,12 +27,72 @@ M.FONT_HEAVY = 'Noto Sans Black'
 -- with `fc-match` before trusting it.
 M.FONT_CLOCK = 'Oswald'
 
+-- Cairo's toy text API binds ONE face and has no per-glyph fallback, so an
+-- emoji in a calendar title drew as tofu in Noto Sans. text/measure/advance
+-- therefore split a string into runs and draw the emoji runs in this face.
+-- Monochrome on purpose: it takes the source colour like any other glyph, so
+-- emoji follow the palette instead of pasting fixed colours onto the card.
+M.FONT_EMOJI = 'Noto Emoji'
+
+-- The face last chosen by M.font(), restored after each emoji run.
+local cur_family, cur_weight
+
 function M.font(cr, family, size, bold)
-  cairo_select_font_face(cr, family, CAIRO_FONT_SLANT_NORMAL,
-    bold and CAIRO_FONT_WEIGHT_BOLD or CAIRO_FONT_WEIGHT_NORMAL)
+  cur_family = family
+  cur_weight = bold and CAIRO_FONT_WEIGHT_BOLD or CAIRO_FONT_WEIGHT_NORMAL
+  cairo_select_font_face(cr, family, CAIRO_FONT_SLANT_NORMAL, cur_weight)
   cairo_set_font_size(cr, size)
 end
 
+-- ponytail: codepoint ranges, not real glyph coverage, and the toy API has no
+-- shaping, so a ZWJ family or a flag draws as its parts. Pango (via lgi) is
+-- the upgrade path if that ever matters. 0x1F000-0x1FAFF only: the Nerd Font
+-- icons the card titles use live in PUA (0xE000+, 0xF0000+) and must stay in
+-- FONT_MONO.
+local function is_emoji(cp)
+  return (cp >= 0x1F000 and cp <= 0x1FAFF) or (cp >= 0x2600 and cp <= 0x27BF)
+end
+
+-- { {text, is_emoji}, ... }, dropping VS16 and ZWJ, which only carry meaning
+-- to a shaper. Plain ASCII and Latin text, and anything that is not valid
+-- UTF-8, come back as a single non-emoji run: no allocation per frame for
+-- the common case, and no error for a bad string (an error is a blank screen).
+local function runs(s)
+  if not s:find('[\226\240-\244]') then return nil end
+  local ok, out = pcall(function()
+    local out, cur, ce = {}, {}, nil
+    for _, cp in utf8.codes(s) do
+      if cp ~= 0xFE0F and cp ~= 0x200D then
+        local e = is_emoji(cp)
+        if e ~= ce and #cur > 0 then
+          out[#out + 1] = { table.concat(cur), ce }
+          cur = {}
+        end
+        cur[#cur + 1], ce = utf8.char(cp), e
+      end
+    end
+    if #cur > 0 then out[#out + 1] = { table.concat(cur), ce } end
+    return out
+  end)
+  return ok and out or nil
+end
+
+-- Calls fn(text) for each run with its face selected, then restores the
+-- caller's face so the next draw call is unaffected.
+local function each_run(cr, list, fn)
+  for _, r in ipairs(list) do
+    local swap = r[2] and cur_family
+    if swap then
+      cairo_select_font_face(cr, M.FONT_EMOJI, CAIRO_FONT_SLANT_NORMAL,
+        CAIRO_FONT_WEIGHT_NORMAL)
+    end
+    fn(r[1])
+    if swap then
+      cairo_select_font_face(cr, cur_family, CAIRO_FONT_SLANT_NORMAL, cur_weight)
+    end
+  end
+end
+
 function M.rgba(cr, c, alpha)
   cairo_set_source_rgba(cr, c[1], c[2], c[3], alpha or c[4] or 1)
 end
@@ -40,7 +100,10 @@ end
 -- Text at (x, y), where y is the BASELINE, not the top of the glyphs.
 function M.text(cr, x, y, s)
   cairo_move_to(cr, x, y)
-  cairo_show_text(cr, s)
+  local list = runs(s)
+  if not list then return cairo_show_text(cr, s) end
+  -- show_text leaves the current point after the run, so runs chain.
+  each_run(cr, list, function(t) cairo_show_text(cr, t) end)
 end
 
 -- Measured width and height of a string under the current font.
@@ -61,8 +124,27 @@ 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
+  local list = runs(s)
+  if not list then
+    cairo_text_extents(cr, s, extents)
+    return extents.width, extents.height
+  end
+  -- Union of each run's ink box, offset by the advances before it. A run
+  -- with no ink (spaces) moves the pen but adds nothing to the box.
+  local pen, x0, x1, y0, y1 = 0, nil, nil, nil, nil
+  each_run(cr, list, function(t)
+    cairo_text_extents(cr, t, extents)
+    if extents.width > 0 then
+      local l = pen + extents.x_bearing
+      x0, x1 = math.min(x0 or l, l), math.max(x1 or l, l + extents.width)
+      y0 = math.min(y0 or extents.y_bearing, extents.y_bearing)
+      local b = extents.y_bearing + extents.height
+      y1 = math.max(y1 or b, b)
+    end
+    pen = pen + extents.x_advance
+  end)
+  if not x0 then return 0, 0 end
+  return x1 - x0, y1 - y0
 end
 
 -- How far the cursor moves after drawing a string. Use this to lay out runs of
@@ -74,8 +156,17 @@ end
 -- 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
+  local list = runs(s)
+  if not list then
+    cairo_text_extents(cr, s, extents)
+    return extents.x_advance
+  end
+  local pen = 0
+  each_run(cr, list, function(t)
+    cairo_text_extents(cr, t, extents)
+    pen = pen + extents.x_advance
+  end)
+  return pen
 end
 
 -- Right-aligned text: x is the RIGHT edge.
diff --git a/test/test_data.lua b/test/test_data.lua
index ec2b6ed..549ce40 100644
--- a/test/test_data.lua
+++ b/test/test_data.lua
@@ -505,3 +505,19 @@ assert(gate(100.0) == true, 'gate: first call opens')
 assert(gate(100.5) == false, 'gate: closed inside the interval')
 assert(gate(101.95) == true, 'gate: opens after it')
 assert(gate(102.0) == false, 'gate: interval restarts from the last open')
+
+-- Emoji fall back to card.FONT_EMOJI: the toy API has no per-glyph fallback,
+-- so without the run split "x🦷" measured a tofu box in Noto Sans.
+do
+  local s = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 10, 10)
+  local cr = cairo_create(s)
+  card.font(cr, 'Noto Emoji', 20, false)
+  local tooth = card.advance(cr, '🦷')
+  card.font(cr, card.FONT_UI, 20, false)
+  local x = card.advance(cr, 'x')
+  assert(math.abs(card.advance(cr, 'x🦷') - (x + tooth)) < 0.01, 'emoji run uses FONT_EMOJI')
+  assert(card.advance(cr, 'x') == x, 'caller face restored after an emoji run')
+  assert(pcall(card.advance, cr, '\240\159'), 'invalid UTF-8 must not raise')
+  cairo_destroy(cr)
+  cairo_surface_destroy(s)
+end