Support overstriking by backspace in PostScript and PDF output.

Of course, this is only a minor improvement; it would be much better
to support non-ASCII characters in these output modes, but that
would require major changes that i'm not going to work on right now.

The main reason for doing this is that it allows to get ASCII output
closer to groff.

1 files changed, 61 insertions, 15 deletions

diff --git a/term_ps.c b/term_ps.c
index 0dc5b999..35eec3c4 100644
--- a/term_ps.c
+++ b/term_ps.c
@@ -59,12 +59,13 @@ struct	termp_ps {
 #define	PS_INLINE	 (1 << 0)	/* we're in a word */
 #define	PS_MARGINS	 (1 << 1)	/* we're in the margins */
 #define	PS_NEWPAGE	 (1 << 2)	/* new page, no words yet */
+#define	PS_BACKSP	 (1 << 3)	/* last character was backspace */
 	size_t		  pscol;	/* visible column (AFM units) */
 	size_t		  psrow;	/* visible row (AFM units) */
 	char		 *psmarg;	/* margin buf */
 	size_t		  psmargsz;	/* margin buf size */
 	size_t		  psmargcur;	/* cur index in margin buf */
-	char		  last;		/* character buffer */
+	char		  last;		/* last non-backspace seen */
 	enum termfont	  lastf;	/* last set font */
 	enum termfont	  nextf;	/* building next font here */
 	size_t		  scale;	/* font scaling factor */
@@ -1047,7 +1048,7 @@ ps_fclose(struct termp *p)
 	 */
 
 	if (p->ps->last != '\0') {
-		assert(p->ps->last != 8);
+		assert( ! (p->ps->flags & PS_BACKSP));
 		if (p->ps->nextf != p->ps->lastf) {
 			ps_pclose(p);
 			ps_setfont(p, p->ps->nextf);
@@ -1066,25 +1067,30 @@ ps_fclose(struct termp *p)
 static void
 ps_letter(struct termp *p, int arg)
 {
+	size_t		savecol;
 	char		c;
 
 	c = arg >= 128 || arg <= 0 ? '?' : arg;
 
 	/*
-	 * When receiving an initial character, merely buffer it,
-	 * because a backspace might follow to specify formatting.
-	 * When receiving a backspace, use the buffered character
-	 * to build the font instruction and clear the buffer.
-	 * Only when there are two non-backspace characters in a row,
-	 * activate the font built so far and print the first of them;
-	 * the second, again, merely gets buffered.
-	 * The final character will get printed from ps_fclose().
+	 * When receiving a backspace, merely flag it.
+	 * We don't know yet whether it is
+	 * a font instruction or an overstrike.
 	 */
 
-	if (c == 8) {
+	if (c == '\b') {
 		assert(p->ps->last != '\0');
-		assert(p->ps->last != 8);
-		if ('_' == p->ps->last) {
+		assert( ! (p->ps->flags & PS_BACKSP));
+		p->ps->flags |= PS_BACKSP;
+		return;
+	}
+
+	/*
+	 * Decode font instructions.
+	 */
+
+	if (p->ps->flags & PS_BACKSP) {
+		if (p->ps->last == '_') {
 			switch (p->ps->nextf) {
 			case TERMFONT_BI:
 				break;
@@ -1094,7 +1100,11 @@ ps_letter(struct termp *p, int arg)
 			default:
 				p->ps->nextf = TERMFONT_UNDER;
 			}
-		} else {
+			p->ps->last = c;
+			p->ps->flags &= ~PS_BACKSP;
+			return;
+		}
+		if (p->ps->last == c) {
 			switch (p->ps->nextf) {
 			case TERMFONT_BI:
 				break;
@@ -1104,8 +1114,26 @@ ps_letter(struct termp *p, int arg)
 			default:
 				p->ps->nextf = TERMFONT_BOLD;
 			}
+			p->ps->flags &= ~PS_BACKSP;
+			return;
 		}
-	} else if (p->ps->last != '\0' && p->ps->last != 8) {
+
+		/*
+		 * This is not a font instruction, but rather
+		 * the next character.  Prepare for overstrike.
+		 */
+
+		savecol = p->ps->pscol;
+	} else
+		savecol = SIZE_MAX;
+
+	/*
+	 * We found the next character, so the font instructions
+	 * for the previous one are complete.
+	 * Use them and print it.
+	 */
+
+	if (p->ps->last != '\0') {
 		if (p->ps->nextf != p->ps->lastf) {
 			ps_pclose(p);
 			ps_setfont(p, p->ps->nextf);
@@ -1113,7 +1141,25 @@ ps_letter(struct termp *p, int arg)
 		p->ps->nextf = TERMFONT_NONE;
 		ps_pletter(p, p->ps->last);
 	}
+
+	/*
+	 * Do not print the current character yet because font
+	 * instructions might follow; only remember it.
+	 * For the first character, nothing else is done.
+	 * The final character will get printed from ps_fclose().
+	 */
+
 	p->ps->last = c;
+
+	/*
+	 * For an overstrike, back up to the previous position.
+	 */
+
+	if (savecol != SIZE_MAX) {
+		ps_pclose(p);
+		p->ps->pscol = savecol;
+		p->ps->flags &= ~PS_BACKSP;
+	}
 }
 
 static void