Support @~ (Symbol font toggle) in -Sq quoted line labels (#8952)

The @~ escape sequence for switching to the Symbol font (Greek letters
  etc.) was ignored in -Sq quoted line labels. The label text was rendered
  via PostScript's show operator in PSL_label.ps, which doesn't understand
  GMT's @~ escape sequences.

  Add PostScript procedures (PSL_split_esc, PSL_has_esc, PSL_show_esc,
  PSL_charpath_esc, PSL_sw_esc) that split label strings on @~ boundaries
  and toggle between the current font and Symbol font for each segment.
  Wrapper functions (PSL_label_show, PSL_label_charpath, PSL_label_sw)
  dispatch to the escape-aware versions only when @~ is present, so labels
  without escapes follow the exact same code path as before.

  For curved text (+v), modify setchar to detect @~ at the current position
  and toggle fonts without rendering, allowing the next real character to
  be placed in the correct font along the path.

  Fixes both straight baseline labels (PSL_ST_place_label*) and curved
  baseline labels (PSL_pathtext/setchar), as well as width calculations
  (PSL_ST_prepare_text, PSL_CT_calcstringwidth).

  Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>"

Author: joa-quim

src/PSL_label.ps

@@ -166,32 +166,47 @@ static char *PSL_label_str =
 "						% same point.\n"
 "\n"
 "/setchar					% ``setchar'' sets the next\n"
-"  { /char str charcount 1 getinterval def	% character in the string along\n"
+"						% character in the string along\n"
 "						% the path and then updates the\n"
 "						% amount of path we have\n"
 "						% exhausted.\n"
-"    /charcount charcount 1 add def		% Increment the character count.\n"
-"    /charwidth char stringwidth pop def		% Find the width of the character.\n"
-"    V cpx cpy itransform T			% Translate to the current\n"
+"  { charcount 1 add str length lt		% Check if at least 2 chars remain\n"
+"    {str charcount get 64 eq str charcount 1 add get 126 eq and} {false} ifelse\n"
+"    {	% Found @~ escape: skip it, toggle font, no rendering\n"
+"      /charcount charcount 2 add def\n"
+"      /psl_ct_sym psl_ct_sym not def\n"
+"      psl_ct_sym {\n"
+"        /psl_ct_origfont currentfont def\n"
+"        /Symbol findfont PSL_get_fontsize scalefont setfont\n"
+"      } {\n"
+"        psl_ct_origfont setfont\n"
+"      } ifelse\n"
+"    }\n"
+"    {	% Normal character rendering\n"
+"      /char str charcount 1 getinterval def\n"
+"      /charcount charcount 1 add def\n"
+"      /charwidth char stringwidth pop def\n"
+"      V cpx cpy itransform T			% Translate to the current\n"
 "						% position in user space.\n"
-"      dy dx atan R				% Rotate the x-axis to coincide\n"
+"        dy dx atan R				% Rotate the x-axis to coincide\n"
 "						% with the current segment.\n"
-"      0 justy M\n"
-"      PSL_font_F {  % Show text normally, if requested\n"
-"        char show}\n"
-"      if\n"
-"      PSL_font_FO { % Fill first then outline, if requested\n"
-"        currentpoint N M V char true charpath fs U V char false charpath S U char E 0 G\n"
-"      } if\n"
-"      PSL_font_OF { % Outline text then fill, if requested\n"
-"        currentpoint N M V char false charpath S U V char true charpath fs U char E 0 G\n"
-"      } if\n"
-"      0 justy neg G currentpoint transform\n"
-"      /cpy exch def /cpx exch def		% Update the current position\n"
-"    						% before we restore ourselves to\n"
+"        0 justy M\n"
+"        PSL_font_F {  % Show text normally, if requested\n"
+"          char show}\n"
+"        if\n"
+"        PSL_font_FO { % Fill first then outline, if requested\n"
+"          currentpoint N M V char true charpath fs U V char false charpath S U char E 0 G\n"
+"        } if\n"
+"        PSL_font_OF { % Outline text then fill, if requested\n"
+"          currentpoint N M V char false charpath S U V char true charpath fs U char E 0 G\n"
+"        } if\n"
+"        0 justy neg G currentpoint transform\n"
+"        /cpy exch def /cpx exch def		% Update the current position\n"
+"      						% before we restore ourselves to\n"
 "						% the untransformed state.\n"
-"    U /setdist setdist charwidth add def	% Increment the distance we have\n"
-"  } def						% covered by setting characters.\n"
+"      U /setdist setdist charwidth add def	% Increment the distance we have\n"
+"    } ifelse					% covered by setting characters.\n"
+"  } def\n"
 "end\n"
 "\n"
 "% PSL LABEL CLIP FUNCTIONS\n"
@@ -336,7 +351,7 @@ static char *PSL_label_str =
 "  0 1 PSL_m1\n"
 "  { /i exch def\n"
 "    PSL_fnt_tmp i get cvx exec					% Get and set this label's font attributes\n"
-"    PSL_width_tmp i PSL_str_tmp i get stringwidth pop put	% Compute width and store in the array\n"
+"    PSL_width_tmp i PSL_str_tmp i get PSL_label_sw put	% Compute width and store in the array\n"
 "  } for\n"
 "} def\n"
 "\n"
@@ -475,6 +490,7 @@ static char *PSL_label_str =
 "    PSL_drawbox		% Want to draw outline of box\n"
 "    {V PSL_setboxpen S U} if N\n"
 "  } if\n"
+"  /psl_ct_sym false def\n"
 "  PSL_CT_placeline psl_label PSL_gap_x PSL_just PSL_height psl_depth PSL_pathtext\n"
 "} def\n"
 "\n"
@@ -629,6 +645,110 @@ static char *PSL_label_str =
 "  PSL_eoclip N					% Set the new clip path, increment clip counter and clear path\n"
 "} def\n"
 "\n"
+"% Escape-aware label rendering procedures.\n"
+"% These handle the @~ escape sequence (Symbol font toggle) in label strings.\n"
+"% When @~ is found, the string is split into segments that alternate between\n"
+"% the current font and the Symbol font at the same size.\n"
+"\n"
+"/PSL_split_esc {	% (string) PSL_split_esc => array of substrings split on @~\n"
+"  /psl_src exch def\n"
+"  /psl_parts 20 array def\n"
+"  /psl_np 0 def\n"
+"  /psl_pos 0 def\n"
+"  {\n"
+"    /psl_found false def\n"
+"    psl_pos 1 psl_src length 2 sub {\n"
+"      /psl_i exch def\n"
+"      psl_src psl_i get 64 eq			% '@' = ASCII 64\n"
+"      psl_src psl_i 1 add get 126 eq and	% '~' = ASCII 126\n"
+"      {\n"
+"        psl_parts psl_np psl_src psl_pos psl_i psl_pos sub getinterval put\n"
+"        /psl_np psl_np 1 add def\n"
+"        /psl_pos psl_i 2 add def\n"
+"        /psl_found true def\n"
+"        exit\n"
+"      } if\n"
+"    } for\n"
+"    psl_found not {exit} if\n"
+"  } loop\n"
+"  psl_pos psl_src length lt {\n"
+"    psl_parts psl_np psl_src psl_pos psl_src length psl_pos sub getinterval put\n"
+"    /psl_np psl_np 1 add def\n"
+"  } if\n"
+"  psl_parts 0 psl_np getinterval\n"
+"} def\n"
+"\n"
+"/PSL_has_esc {	% (string) PSL_has_esc => bool  -- true if string contains @~\n"
+"  /psl_ts exch def\n"
+"  /psl_he false def\n"
+"  0 1 psl_ts length 2 sub {\n"
+"    /psl_ti exch def\n"
+"    psl_ts psl_ti get 64 eq psl_ts psl_ti 1 add get 126 eq and\n"
+"    {/psl_he true def exit} if\n"
+"  } for\n"
+"  psl_he\n"
+"} def\n"
+"\n"
+"/PSL_get_fontsize {	% => fontsize  -- extract size from current font\n"
+"  currentfont /FontMatrix get 0 get 1000 mul\n"
+"} def\n"
+"\n"
+"/PSL_show_esc {	% (string) PSL_show_esc => --  -- show with @~ font toggling\n"
+"  PSL_split_esc\n"
+"  /psl_origfont currentfont def\n"
+"  /psl_sym false def\n"
+"  /psl_fsz PSL_get_fontsize def\n"
+"  { /psl_seg exch def\n"
+"    psl_seg length 0 gt {psl_seg show} if\n"
+"    /psl_sym psl_sym not def\n"
+"    psl_sym {/Symbol findfont psl_fsz scalefont setfont}\n"
+"            {psl_origfont setfont} ifelse\n"
+"  } forall\n"
+"  psl_origfont setfont\n"
+"} def\n"
+"\n"
+"/PSL_charpath_esc {	% (string) PSL_charpath_esc => --  -- false charpath with @~ toggling\n"
+"  PSL_split_esc\n"
+"  /psl_origfont currentfont def\n"
+"  /psl_sym false def\n"
+"  /psl_fsz PSL_get_fontsize def\n"
+"  { /psl_seg exch def\n"
+"    psl_seg length 0 gt {psl_seg false charpath} if\n"
+"    /psl_sym psl_sym not def\n"
+"    psl_sym {/Symbol findfont psl_fsz scalefont setfont}\n"
+"            {psl_origfont setfont} ifelse\n"
+"  } forall\n"
+"  psl_origfont setfont\n"
+"} def\n"
+"\n"
+"/PSL_sw_esc {	% (string) PSL_sw_esc => width  -- stringwidth with @~ toggling\n"
+"  PSL_split_esc\n"
+"  /psl_origfont currentfont def\n"
+"  /psl_sym false def\n"
+"  /psl_fsz PSL_get_fontsize def\n"
+"  /psl_tw 0 def\n"
+"  { /psl_seg exch def\n"
+"    psl_seg length 0 gt {/psl_tw psl_tw psl_seg stringwidth pop add def} if\n"
+"    /psl_sym psl_sym not def\n"
+"    psl_sym {/Symbol findfont psl_fsz scalefont setfont}\n"
+"            {psl_origfont setfont} ifelse\n"
+"  } forall\n"
+"  psl_origfont setfont\n"
+"  psl_tw\n"
+"} def\n"
+"\n"
+"/PSL_label_show {	% (string) PSL_label_show => --\n"
+"  dup PSL_has_esc {PSL_show_esc} {show} ifelse\n"
+"} def\n"
+"\n"
+"/PSL_label_charpath {	% (string) PSL_label_charpath => --\n"
+"  dup PSL_has_esc {PSL_charpath_esc} {false charpath} ifelse\n"
+"} def\n"
+"\n"
+"/PSL_label_sw {	% (string) PSL_label_sw => width\n"
+"  dup PSL_has_esc {PSL_sw_esc} {stringwidth pop} ifelse\n"
+"} def\n"
+"\n"
 "/PSL_ST_prepare_text		% Compute various dimensions and coordinates for one label\n"
 "{ % The current label has index psl_k\n"
 "  /psl_xp PSL_txt_x psl_k get def		% Get text placement x coordinate\n"
@@ -640,7 +760,7 @@ static char *PSL_label_str =
 "  /PSL_just PSL_label_justify psl_k get def	% Get text justification (1-11)\n"
 "  /PSL_justx PSL_just 4 mod 1 sub 2 div neg def % This is 0, -0.5, or -1 for relative x-shift \n"
 "  /PSL_justy PSL_just 4 idiv 2 div neg def	% This is 0, -0.5, or -1 for relative y-shift \n"
-"  /psl_SW psl_label stringwidth pop def		% Width of current label space\n"
+"  /psl_SW psl_label PSL_label_sw def		% Width of current label space\n"
 "  /psl_boxW psl_SW PSL_gap_x 2 mul add def	% Width of current label space including clearance\n"
 "  /psl_x0 psl_SW PSL_justx mul def		% (psl_x0,psl_y0) is rotated/adjusted text LL point on inside rectangle relative to psl_xp,psl_yp\n"
 "  /psl_y0 PSL_justy PSL_height mul def		%\n"
@@ -680,23 +800,23 @@ static char *PSL_label_str =
 "{\n"
 "    V psl_xp psl_yp T psl_angle R % Set origin at text point and rotate the coordinate system to follow baseline text\n"
 "    psl_SW PSL_justx mul psl_y0 M % Goto LL point on label\n"
-"    psl_label dup sd neg 0 exch G show  % Place the text, adjust vertically for any depth below baseline\n"
+"    psl_label dup sd neg 0 exch G PSL_label_show  % Place the text, adjust vertically for any depth below baseline\n"
 "    U         % Undo damage to coordinate system\n"
 "} def\n"
 "\n"
 "/PSL_ST_place_label_FO % Just place the current label by filling it, then outlining it\n"
 "{\n"
 "    V psl_xp psl_yp T psl_angle R % Set origin at text point and rotate the coordinate system to follow baseline text\n"
 "    psl_SW PSL_justx mul psl_y0 M % Goto LL point on label\n"
-"    psl_label dup sd neg 0 exch G false charpath V fs U S N % Place the text, adjust vertically for any depth below baseline\n"
+"    psl_label dup sd neg 0 exch G PSL_label_charpath V fs U S N % Place the text, adjust vertically for any depth below baseline\n"
 "    U         % Undo damage to coordinate system\n"
 "} def\n"
 "\n"
 "/PSL_ST_place_label_OF % Just place the current label by drawing outline, then filling it\n"
 "{\n"
 "    V psl_xp psl_yp T psl_angle R % Set origin at text point and rotate the coordinate system to follow baseline text\n"
 "    psl_SW PSL_justx mul psl_y0 M % Goto LL point on label\n"
-"    psl_label dup sd neg 0 exch G false charpath V S U fs N % Place the text, adjust vertically for any depth below baseline\n"
+"    psl_label dup sd neg 0 exch G PSL_label_charpath V S U fs N % Place the text, adjust vertically for any depth below baseline\n"
 "    U         % Undo damage to coordinate system\n"
 "} def\n"
 "\n"