[Bug 1961455]: Draw underlines and overstrikes when using Xft for font rendering

1 files changed, 57 insertions, 4 deletions

diff --git a/unix/tkUnixRFont.c b/unix/tkUnixRFont.c
index b3d5ce4..f580b2f 100644
--- a/unix/tkUnixRFont.c
+++ b/unix/tkUnixRFont.c
@@ -8,7 +8,7 @@
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tkUnixRFont.c,v 1.24.2.1 2009/09/10 12:47:15 dkf Exp $
+ * RCS: @(#) $Id: tkUnixRFont.c,v 1.24.2.2 2009/10/10 19:38:27 dkf Exp $
  */
 
 #include "tkUnixInt.h"
@@ -35,7 +35,6 @@ typedef struct {
     XftDraw *ftDraw;
     XftColor color;
 } UnixFtFont;
-
 
 /*
  * Package initialization:
@@ -261,6 +260,44 @@ InitFont(
     GetTkFontAttributes(ftFont, &fontPtr->font.fa);
     GetTkFontMetrics(ftFont, &fontPtr->font.fm);
 
+    /*
+     * Fontconfig can't report any information about the position or thickness
+     * of underlines or overstrikes. Thus, we use some defaults that are
+     * hacked around from backup defaults in tkUnixFont.c, which are in turn
+     * based on recommendations in the X manual. The comments from that file
+     * leading to these computations were:
+     *
+     *	    If the XA_UNDERLINE_POSITION property does not exist, the X manual
+     *	    recommends using half the descent.
+     *
+     *	    If the XA_UNDERLINE_THICKNESS property does not exist, the X
+     *	    manual recommends using the width of the stem on a capital letter.
+     *	    I don't know of a way to get the stem width of a letter, so guess
+     *	    and use 1/3 the width of a capital I.
+     *
+     * Note that nothing corresponding to *either* property is reported by
+     * Fontconfig at all. [Bug 1961455]
+     */
+
+    {
+	TkFont *fPtr = &fontPtr->font;
+	int iWidth;
+
+	fPtr->underlinePos = fPtr->fm.descent / 2;
+	Tk_MeasureChars((Tk_Font) fPtr, "I", 1, -1, 0, &iWidth);
+	fPtr->underlineHeight = iWidth / 3;
+	if (fPtr->underlineHeight == 0) {
+	    fPtr->underlineHeight = 1;
+	}
+	if (fPtr->underlineHeight + fPtr->underlinePos > fPtr->fm.descent) {
+	    fPtr->underlineHeight = fPtr->fm.descent - fPtr->underlinePos;
+	    if (fPtr->underlineHeight == 0) {
+		fPtr->underlinePos--;
+		fPtr->underlineHeight = 1;
+	    }
+	}
+    }
+
     return fontPtr;
 }
 
@@ -404,6 +441,9 @@ TkpGetFontFromAttributes(
 	FcPatternDestroy(pattern);
 	return NULL;
     }
+
+    fontPtr->font.fa.underline = faPtr->underline;
+    fontPtr->font.fa.overstrike = faPtr->overstrike;
     return &fontPtr->font;
 }
 
@@ -671,7 +711,7 @@ Tk_DrawChars(
     UnixFtFont *fontPtr = (UnixFtFont *) tkfont;
     XGCValues values;
     XColor xcolor;
-    int clen, nspec;
+    int clen, nspec, xStart = x;
     XftGlyphFontSpec specs[NUM_SPEC];
     XGlyphInfo metrics;
 
@@ -711,7 +751,7 @@ Tk_DrawChars(
 	     * This should not happen, but it can.
 	     */
 
-	    return;
+	    goto doUnderlineStrikeout;
 	}
 	source += clen;
 	numBytes -= clen;
@@ -737,4 +777,17 @@ Tk_DrawChars(
     if (nspec) {
 	XftDrawGlyphFontSpec(fontPtr->ftDraw, &fontPtr->color, specs, nspec);
     }
+
+  doUnderlineStrikeout:
+    if (fontPtr->font.fa.underline != 0) {
+	XFillRectangle(display, drawable, gc, xStart,
+		y + fontPtr->font.underlinePos, (unsigned) (x - xStart),
+		(unsigned) fontPtr->font.underlineHeight);
+    }
+    if (fontPtr->font.fa.overstrike != 0) {
+	y -= fontPtr->font.fm.descent + (fontPtr->font.fm.ascent) / 10;
+	XFillRectangle(display, drawable, gc, xStart, y,
+		(unsigned) (x - xStart),
+		(unsigned) fontPtr->font.underlineHeight);
+    }
 }