Partial implementation of .Bd -centered.

In groff, .Bd -centered operates in fill mode, which is relatively
hard to implement, while this implementation operates in non-fill
mode so far.  As long as you pay attention that your lines do not
overflow, it works.  To make sure that rendering is the same for
mandoc and groff, it is recommended to insert .br between lines
for now.  This implementation will need improvement later.

3 files changed, 15 insertions, 4 deletions

diff --git a/mdoc.h b/mdoc.h
index 43ab3b5c..f2341a47 100644
--- a/mdoc.h
+++ b/mdoc.h
@@ -280,7 +280,7 @@ enum	mdoc_list {
 
 enum	mdoc_disp {
 	DISP__NONE = 0,
-	DISP_centred, /* -centered */
+	DISP_centered, /* -centered */
 	DISP_ragged, /* -ragged */
 	DISP_unfilled, /* -unfilled */
 	DISP_filled, /* -filled */
diff --git a/mdoc_term.c b/mdoc_term.c
index 7ca42a50..e05b9f96 100644
--- a/mdoc_term.c
+++ b/mdoc_term.c
@@ -1571,7 +1571,7 @@ termp_fa_pre(DECL_ARGS)
 static int
 termp_bd_pre(DECL_ARGS)
 {
-	size_t			 tabwidth, rm, rmax;
+	size_t			 tabwidth, lm, len, rm, rmax;
 	struct mdoc_node	*nn;
 
 	if (MDOC_BLOCK == n->type) {
@@ -1592,18 +1592,29 @@ termp_bd_pre(DECL_ARGS)
 	 */
 
 	if (DISP_literal != n->norm->Bd.type &&
-	    DISP_unfilled != n->norm->Bd.type)
+	    DISP_unfilled != n->norm->Bd.type &&
+	    DISP_centered != n->norm->Bd.type)
 		return(1);
 
 	tabwidth = p->tabwidth;
 	if (DISP_literal == n->norm->Bd.type)
 		p->tabwidth = term_len(p, 8);
 
+	lm = p->offset;
 	rm = p->rmargin;
 	rmax = p->maxrmargin;
 	p->rmargin = p->maxrmargin = TERM_MAXMARGIN;
 
 	for (nn = n->child; nn; nn = nn->next) {
+		if (DISP_centered == n->norm->Bd.type) {
+			if (MDOC_TEXT == nn->type) {
+				len = term_strlen(p, nn->string);
+				p->offset = len >= rm ? 0 :
+				    lm + len >= rm ? rm - len :
+				    (lm + rm - len) / 2;
+			} else
+				p->offset = lm;
+		}
 		print_mdoc_node(p, pair, meta, nn);
 		/*
 		 * If the printed node flushes its own line, then we
diff --git a/mdoc_validate.c b/mdoc_validate.c
index 6aaddaa8..c8596140 100644
--- a/mdoc_validate.c
+++ b/mdoc_validate.c
@@ -802,7 +802,7 @@ pre_bd(PRE_ARGS)
 
 		switch (argv->arg) {
 		case MDOC_Centred:
-			dt = DISP_centred;
+			dt = DISP_centered;
 			break;
 		case MDOC_Ragged:
 			dt = DISP_ragged;