[201_104] Fix inner product symbol not rendering on Tab cycling popup window (#3104)

Author: 1sh-repalto

devel/201_104.md

@@ -0,0 +1,27 @@
+# [201_104] Fix inner product symbol not rendering in Tab cycling popup
+
+### What
+Fixed `⟨⟩` (angle bracket pair) showing as a red broken symbol in the Tab cycling completion popup when typing `<` in math mode.
+
+### Why
+The Tab cycling popup renders symbol labels using `math_font_rep`. Its `get_extents`, `get_xpositions`, and `draw_fixed` methods all passed the full string to `search_font`, which only handles single math symbols. For a bracket pair like `"<langle><rangle>"` (two concatenated TeXmacs symbols), `search_font` fails — it is not a single dictionary entry and the character fallback rejects `<` — so it returns `error_font`, which draws in red.
+
+### How
+Modified `src/Graphics/Fonts/math_font.cpp`.
+
+Added a single-char fast path (via `tm_char_forwards`) to `get_extents`, `get_xpositions`, and both `draw_fixed` overloads. Single characters use the original `search_font` lookup unchanged. Multi-character strings iterate character by character:
+
+- `get_extents`: accumulates per-symbol metrics, combining advance widths and taking the union of ink bounds.
+- `get_xpositions`: fills the position array by accumulating advance widths per symbol.
+- `draw_fixed(x, y)`: draws each symbol at its accumulated x-offset.
+- `draw_fixed(x, y, xk)`: delegates to `font_rep::draw_fixed` (base class already iterates char-by-char).
+
+No Scheme-level changes needed — `lambda-to-symbol` in `math-edit.scm` already returns `(string-append lb rb)`.
+
+### How to test
+1. Open Mogan Editor and create a new document.
+2. Enter math mode (`$` or via Insert → Math).
+3. Type `<` and press `Tab` to open the cycling popup.
+4. **Verify**: The `⟨⟩` entry displays correctly (not in red).
+5. Press `Tab` to cycle through variants and select `⟨⟩`.
+6. **Verify**: The correct angle bracket pair is inserted in the document.

src/Graphics/Fonts/math_font.cpp

@@ -175,39 +175,118 @@ math_font_rep::supports (string c) {
 
 void
 math_font_rep::get_extents (string s, metric& ex) {
-  font fn;
-  search_font (s, fn);
-  fn->get_extents (s, ex);
+  // Fast path: single TeXmacs character
+  int i= 0;
+  tm_char_forwards (s, i);
+  if (i >= N (s)) {
+    font fn;
+    search_font (s, fn);
+    fn->get_extents (s, ex);
+    return;
+  }
+  // Multi-character string (e.g. "<langle><rangle>"): accumulate extents
+  // character by character so each symbol is looked up individually.
+  metric ey;
+  SI     advance= 0;
+  bool   first  = true;
+  i             = 0;
+  while (i < N (s)) {
+    int j= i;
+    tm_char_forwards (s, j);
+    get_extents (s (i, j), ey);
+    if (first) {
+      ex[0]= ey[0];
+      first= false;
+    }
+    else {
+      ex->x2= advance + ey->x2;
+      ex->y1= min (ex->y1, ey->y1);
+      ex->y2= max (ex->y2, ey->y2);
+      ex->x3= min (ex->x3, advance + ey->x3);
+      ex->y3= min (ex->y3, ey->y3);
+      ex->x4= max (ex->x4, advance + ey->x4);
+      ex->y4= max (ex->y4, ey->y4);
+    }
+    advance+= ey->x2;
+    i= j;
+  }
 }
 
 void
 math_font_rep::get_xpositions (string s, SI* xpos) {
   if (s == "") return;
-  font   fn;
-  string r= s;
-  search_font (r, fn);
-  if (r == s) fn->get_xpositions (s, xpos);
-  else if (N (r) != 1) font_rep::get_xpositions (s, xpos);
-  else {
-    int i, n= N (s);
-    for (i= 1; i < n; i++)
-      xpos[i]= 0;
-    fn->get_xpositions (r, xpos + n - 1);
+  // Fast path: single TeXmacs character
+  int i= 0;
+  tm_char_forwards (s, i);
+  if (i >= N (s)) {
+    font   fn;
+    string r= s;
+    search_font (r, fn);
+    if (r == s) fn->get_xpositions (s, xpos);
+    else if (N (r) != 1) font_rep::get_xpositions (s, xpos);
+    else {
+      int k, n= N (s);
+      for (k= 1; k < n; k++)
+        xpos[k]= 0;
+      fn->get_xpositions (r, xpos + n - 1);
+    }
+    return;
+  }
+  // Multi-character string: compute positions character by character.
+  xpos[0]   = 0;
+  SI advance= 0;
+  i         = 0;
+  while (i < N (s)) {
+    int j= i;
+    tm_char_forwards (s, j);
+    metric ex;
+    get_extents (s (i, j), ex);
+    advance+= ex->x2;
+    xpos[j]= advance;
+    i      = j;
   }
 }
 
 void
 math_font_rep::draw_fixed (renderer ren, string s, SI x, SI y) {
-  font fn;
-  search_font (s, fn);
-  fn->draw_fixed (ren, s, x, y);
+  // Fast path: single TeXmacs character
+  int i= 0;
+  tm_char_forwards (s, i);
+  if (i >= N (s)) {
+    font fn;
+    search_font (s, fn);
+    fn->draw_fixed (ren, s, x, y);
+    return;
+  }
+  // Multi-character string: draw each symbol at its own x-advance offset.
+  SI advance= 0;
+  i         = 0;
+  while (i < N (s)) {
+    int j= i;
+    tm_char_forwards (s, j);
+    string c= s (i, j);
+    draw_fixed (ren, c, x + advance, y);
+    metric ex;
+    get_extents (c, ex);
+    advance+= ex->x2;
+    i= j;
+  }
 }
 
 void
 math_font_rep::draw_fixed (renderer ren, string s, SI x, SI y, SI xk) {
-  font fn;
-  search_font (s, fn);
-  fn->draw_fixed (ren, s, x, y, xk);
+  // Fast path: single TeXmacs character
+  int i= 0;
+  tm_char_forwards (s, i);
+  if (i >= N (s)) {
+    font fn;
+    search_font (s, fn);
+    fn->draw_fixed (ren, s, x, y, xk);
+    return;
+  }
+  // Multi-character string: delegate to base class which iterates char-by-char
+  // using get_xpositions (now consistent) and calls single-char draw_fixed.
+  font_rep::draw_fixed (ren, s, x, y, xk);
 }
 
 font