Begin cleaning up scaling units.

Start with the horizontal terminal specifiers, making sure that they match
up with troff.
Then move on to PS, PDF, and HTML, noting that we stick to the terminal
default width for "u".
Lastly, fix some completely-wrong documentation and note that we diverge
from troff w/r/t "u".

4 files changed, 55 insertions, 27 deletions

diff --git a/html.c b/html.c
index b41a7f61..d5021860 100644
--- a/html.c
+++ b/html.c
@@ -760,6 +760,8 @@ bufcat_su(struct html *h, const char *p, const struct roffsu *su)
 	v = su->scale;
 	if (SCALE_MM == su->unit && 0.0 == (v /= 100.0))
 		v = 1.0;
+	else if (SCALE_BU == su->unit)
+		v /= 24.0;
 
 	bufcat_fmt(h, "%s: %.2f%s;", p, v, roffscales[su->unit]);
 }
diff --git a/roff.7 b/roff.7
index 4ca48a98..03c1aad2 100644
--- a/roff.7
+++ b/roff.7
@@ -239,8 +239,9 @@ pica (~1/6 inch)
 .It p
 point (~1/72 inch)
 .It f
-synonym for
+scale
 .Sq u
+by 65536
 .It v
 default vertical span
 .It m
@@ -254,7 +255,7 @@ width of rendered
 .Pq en
 character
 .It u
-default horizontal span
+default horizontal span for the terminal
 .It M
 mini-em (~1/100 em)
 .El
@@ -262,7 +263,6 @@ mini-em (~1/100 em)
 Using anything other than
 .Sq m ,
 .Sq n ,
-.Sq u ,
 or
 .Sq v
 is necessarily non-portable across output media.
@@ -1348,6 +1348,12 @@ refers to groff version 1.15.
 .Pp
 .Bl -dash -compact
 .It
+The
+.Sq u
+scaling unit is the default terminal unit.
+In traditional troff systems, this unit would change depending on the
+output media.
+.It
 In mandoc, the
 .Sx \&EQ ,
 .Sx \&TE ,
diff --git a/term_ascii.c b/term_ascii.c
index 3eb03801..2c11a79c 100644
--- a/term_ascii.c
+++ b/term_ascii.c
@@ -230,32 +230,42 @@ ascii_hspan(const struct termp *p, const struct roffsu *su)
 	double		 r;
 
 	/*
-	 * Approximate based on character width.  These are generated
-	 * entirely by eyeballing the screen, but appear to be correct.
+	 * Approximate based on character width.
+	 * None of these will be actually correct given that an inch on
+	 * the screen depends on character size, terminal, etc., etc.
 	 */
-
 	switch (su->unit) {
+	case SCALE_BU:
+		r = su->scale * 10.0 / 240.0;
+		break;
 	case SCALE_CM:
-		r = su->scale * 4.0;
+		r = su->scale * 10.0 / 2.54;
+		break;
+	case SCALE_FS:
+		r = su->scale * 2730.666;
 		break;
 	case SCALE_IN:
 		r = su->scale * 10.0;
 		break;
+	case SCALE_MM:
+		r = su->scale / 100.0;
+		break;
 	case SCALE_PC:
-		r = (su->scale * 10.0) / 6.0;
+		r = su->scale * 10.0 / 6.0;
 		break;
 	case SCALE_PT:
-		r = (su->scale * 10.0) / 72.0;
-		break;
-	case SCALE_MM:
-		r = su->scale / 1000.0;
+		r = su->scale * 10.0 / 72.0;
 		break;
 	case SCALE_VS:
 		r = su->scale * 2.0 - 1.0;
 		break;
-	default:
+	case SCALE_EN:
+	case SCALE_EM:
 		r = su->scale;
 		break;
+	case SCALE_MAX:
+		abort();
+		break;
 	}
 
 	return(r);
diff --git a/term_ps.c b/term_ps.c
index 37020aa2..24342f74 100644
--- a/term_ps.c
+++ b/term_ps.c
@@ -1115,31 +1115,41 @@ ps_hspan(const struct termp *p, const struct roffsu *su)
 	 * All of these measurements are derived by converting from the
 	 * native measurement to AFM units.
 	 */
-
 	switch (su->unit) {
-	case SCALE_CM:
-		r = PNT2AFM(p, su->scale * 28.34);
-		break;
-	case SCALE_IN:
-		r = PNT2AFM(p, su->scale * 72.0);
-		break;
-	case SCALE_PC:
-		r = PNT2AFM(p, su->scale * 12.0);
+	case SCALE_BU:
+		/*
+		 * Traditionally, the default unit is fixed to the
+		 * output media.  So this would refer to the point.  In
+		 * mandoc(1), however, we stick to the default terminal
+		 * scaling unit so that output is the same regardless
+		 * the media.
+		 */
+		r = PNT2AFM(p, su->scale * 72.0 / 240.0);
 		break;
-	case SCALE_PT:
-		r = PNT2AFM(p, su->scale * 100.0);
+	case SCALE_CM:
+		r = PNT2AFM(p, su->scale * 72.0 / 2.54);
 		break;
 	case SCALE_EM:
 		r = su->scale *
 		    fonts[(int)TERMFONT_NONE].gly[109 - 32].wx;
 		break;
-	case SCALE_MM:
-		r = PNT2AFM(p, su->scale * 2.834);
-		break;
 	case SCALE_EN:
 		r = su->scale *
 		    fonts[(int)TERMFONT_NONE].gly[110 - 32].wx;
 		break;
+	case SCALE_IN:
+		r = PNT2AFM(p, su->scale * 72.0);
+		break;
+	case SCALE_MM:
+		r = su->scale *
+		    fonts[(int)TERMFONT_NONE].gly[109 - 32].wx / 100.0;
+		break;
+	case SCALE_PC:
+		r = PNT2AFM(p, su->scale * 12.0);
+		break;
+	case SCALE_PT:
+		r = PNT2AFM(p, su->scale * 1.0);
+		break;
 	case SCALE_VS:
 		r = su->scale * p->ps->lineheight;
 		break;