Support SGR 9 for strikethrough effect on text.

This is mostly easy: it's just like drawing an underline, except that
you put it at a different height in the character cell. The only
question is _where_ in the character cell.

Pango, and Windows GetOutlineTextMetrics, will tell you exactly where
the font wants to have it. Following xterm, I fall back to 3/8 of the
font's ascent (above the baseline) if either of those is unavailable.

putty.h

@@ -106,6 +106,7 @@
 #define ATTR_BGMASK  0x003FE00U
 #define ATTR_COLOURS 0x003FFFFU
 #define ATTR_DIM     0x1000000U
+#define ATTR_STRIKE  0x2000000U
 #define ATTR_FGSHIFT 0
 #define ATTR_BGSHIFT 9
 

terminal.c

@@ -4132,6 +4132,9 @@ static void term_out(Terminal *term)
                             case 7:       /* enable reverse video */
                               term->curr_attr |= ATTR_REVERSE;
                               break;
+                            case 9:       /* enable strikethrough */
+                              term->curr_attr |= ATTR_STRIKE;
+                              break;
                             case 10:      /* SCO acs off */
                               compatibility(SCOANSI);
                               if (term->no_remote_charset) break;
@@ -4160,6 +4163,9 @@ static void term_out(Terminal *term)
                               compatibility2(OTHER, VT220);
                               term->curr_attr &= ~ATTR_REVERSE;
                               break;
+                            case 29:      /* disable strikethrough */
+                              term->curr_attr &= ~ATTR_STRIKE;
+                              break;
                             case 30:
                             case 31:
                             case 32:

unix/gtkfont.c

@@ -511,6 +511,7 @@ static unifont *x11font_create(GtkWidget *widget, const char *name,
     xfont->u.height = xfont->u.ascent + xfont->u.descent;
     xfont->u.public_charset = pubcs;
     xfont->u.want_fallback = true;
+    xfont->u.strikethrough_y = xfont->u.ascent - (xfont->u.ascent * 3 / 8);
 #ifdef DRAW_TEXT_GDK
     xfont->u.preferred_drawtype = DRAWTYPE_GDK;
 #elif defined DRAW_TEXT_CAIRO
@@ -1463,6 +1464,9 @@ static unifont *pangofont_create_internal(GtkWidget *widget,
     pfont->u.descent =
         PANGO_PIXELS_CEIL(pango_font_metrics_get_descent(metrics));
     pfont->u.height = pfont->u.ascent + pfont->u.descent;
+    pfont->u.strikethrough_y =
+        PANGO_PIXELS(pango_font_metrics_get_ascent(metrics) -
+                     pango_font_metrics_get_strikethrough_position(metrics));
     pfont->u.want_fallback = false;
 #ifdef DRAW_TEXT_CAIRO
     pfont->u.preferred_drawtype = DRAWTYPE_CAIRO;
@@ -2242,6 +2246,7 @@ unifont *multifont_create(GtkWidget *widget, const char *name,
     mfont->u.ascent = font->ascent;
     mfont->u.descent = font->descent;
     mfont->u.height = font->height;
+    mfont->u.strikethrough_y = font->strikethrough_y;
     mfont->u.public_charset = font->public_charset;
     mfont->u.want_fallback = false; /* shouldn't be needed, but just in case */
     mfont->u.preferred_drawtype = font->preferred_drawtype;

unix/gtkfont.h

@@ -67,7 +67,7 @@ typedef struct unifont {
     /*
      * Font dimensions needed by clients.
      */
-    int width, height, ascent, descent;
+    int width, height, ascent, descent, strikethrough_y;
 
     /*
      * Indicates whether this font is capable of handling all glyphs

unix/gtkwin.c

@@ -3887,6 +3887,14 @@ static void do_text_internal(
                   y*inst->font_height + uheight + inst->window_border);
     }
 
+    if (attr & ATTR_STRIKE) {
+        int sheight = inst->fonts[fontid]->strikethrough_y;
+        draw_line(inst, x*inst->font_width+inst->window_border,
+                  y*inst->font_height + sheight + inst->window_border,
+                  (x+len)*widefactor*inst->font_width-1+inst->window_border,
+                  y*inst->font_height + sheight + inst->window_border);
+    }
+
     if ((lattr & LATTR_MODE) != LATTR_NORM) {
         draw_stretch_after(inst,
                            x*inst->font_width+inst->window_border,

windows/window.c

@@ -187,7 +187,7 @@ static bool bold_colours;
 static enum {
     UND_LINE, UND_FONT
 } und_mode;
-static int descent;
+static int descent, font_strikethrough_y;
 
 #define NCFGCOLOURS 22
 #define NEXTCOLOURS 240
@@ -1490,6 +1490,7 @@ static int get_font_width(HDC hdc, const TEXTMETRIC *tm)
 static void init_fonts(int pick_width, int pick_height)
 {
     TEXTMETRIC tm;
+    OUTLINETEXTMETRIC otm;
     CPINFO cpinfo;
     FontSpec *font;
     int fontsize[3];
@@ -1539,6 +1540,10 @@ static void init_fonts(int pick_width, int pick_height)
 
     SelectObject(hdc, fonts[FONT_NORMAL]);
     GetTextMetrics(hdc, &tm);
+    if (GetOutlineTextMetrics(hdc, sizeof(otm), &otm))
+        font_strikethrough_y = tm.tmAscent - otm.otmsStrikeoutPosition;
+    else
+        font_strikethrough_y = tm.tmAscent - (tm.tmAscent * 3 / 8);
 
     GetObject(fonts[FONT_NORMAL], sizeof(LOGFONT), &lfont);
 
@@ -3462,6 +3467,25 @@ static void sys_cursor_update(void)
     ImmReleaseContext(wgs.term_hwnd, hIMC);
 }
 
+static void draw_horizontal_line_on_text(int y, int lattr, RECT line_box,
+                                         COLORREF colour)
+{
+    if (lattr == LATTR_TOP || lattr == LATTR_BOT) {
+        y *= 2;
+        if (lattr == LATTR_BOT)
+            y -= font_height;
+    }
+
+    if (!(0 <= y && y < font_height))
+        return;
+
+    HPEN oldpen = SelectObject(wintw_hdc, CreatePen(PS_SOLID, 0, colour));
+    MoveToEx(wintw_hdc, line_box.left, line_box.top + y, NULL);
+    LineTo(wintw_hdc, line_box.right, line_box.top + y);
+    oldpen = SelectObject(wintw_hdc, oldpen);
+    DeleteObject(oldpen);
+}
+
 /*
  * Draw a line of text in the window, at given character
  * coordinates, in given attributes.
@@ -3838,20 +3862,13 @@ static void do_text_internal(
         SetBkMode(wintw_hdc, TRANSPARENT);
         opaque = false;
     }
-    if (lattr != LATTR_TOP && (force_manual_underline ||
-                               (und_mode == UND_LINE
-                                && (attr & ATTR_UNDER)))) {
-        HPEN oldpen;
-        int dec = descent;
-        if (lattr == LATTR_BOT)
-            dec = dec * 2 - font_height;
 
-        oldpen = SelectObject(wintw_hdc, CreatePen(PS_SOLID, 0, fg));
+    if (lattr != LATTR_TOP && (force_manual_underline ||
-        MoveToEx(wintw_hdc, line_box.left, line_box.top + dec, NULL);
+                               (und_mode == UND_LINE && (attr & ATTR_UNDER))))
-        LineTo(wintw_hdc, line_box.right, line_box.top + dec);
+        draw_horizontal_line_on_text(descent, lattr, line_box, fg);
-        oldpen = SelectObject(wintw_hdc, oldpen);
+
-        DeleteObject(oldpen);
+    if (attr & ATTR_STRIKE)
-    }
+        draw_horizontal_line_on_text(font_strikethrough_y, lattr, line_box, fg);
 }
 
 /*