fix for PR#18915; thanks to Trevor Davis

git-svn-id: https://svn.r-project.org/R/trunk@88387 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: murrell

doc/NEWS.Rd

@@ -165,6 +165,10 @@
       documented to work in concordance with \code{==} and as an exception
       to the typical \code{match()} behaviour which relies on
       \dQuote{univariate} \code{mtfrm()} alone.
+
+      \item It is now possible to convert \emph{to} \code{"snpc"} units
+      via, e.g., \code{grid::convertWidth()}, fixing \PR{18915}. Thanks to
+      \I{Trevor Davis}.
     }
   }
 }

src/library/grid/src/unit.c

@@ -1255,6 +1255,17 @@ double transformFromINCHES(double value, int unit,
     case L_LINES:
 	result = (result*72)/(gc->ps*gc->cex*gc->lineheight);
 	break;
+    case L_SNPC:        
+	if (thisCM < 1e-6 || otherCM < 1e-6) {
+            if (result != 0)
+                error(_("Viewport has zero dimension(s)"));
+        } else {
+            if (thisCM <= otherCM)
+                result = result/(thisCM/2.54);
+            else
+                result = result/(otherCM/2.54);
+        }
+        break;
     case L_MM:
 	result = result*2.54*10;
 	break;
@@ -1282,7 +1293,6 @@ double transformFromINCHES(double value, int unit,
 	 * I'm not sure the remaining ones makes any sense.
 	 * For simplicity, these are just forbidden for now.
 	 */
-    case L_SNPC:        
     case L_MYCHAR:
     case L_MYLINES:
     case L_STRINGWIDTH:

src/library/grid/tests/units.R

@@ -178,3 +178,24 @@ unitCheck(sum(u1, u2),
           sum(unit(c(0.4, .4, .1, .1), c("in", "mm", "in", "mm"))))
 unitCheck(sum(unit.c(u1, u2)),
           sum(unit(c(0.4, .4, .1, .1), c("in", "mm", "in", "mm"))))
+
+# Convert to snpc units
+pushViewport(viewport(width = unit(1, "inch"), height = unit(2, "inch")))
+unitCheck(unit(1, "inch") |> convertWidth("snpc") |> convertWidth("inch"),
+          unit(1, "inch"))
+unitCheck(unit(0.5, "npc") |> convertY("snpc") |> convertY("npc"),
+          unit(0.5, "npc"))
+popViewport()
+# Zero-dimension viewport edge cases
+pushViewport(viewport(width = unit(1, "inch"), height = unit(0, "inch")))
+unitCheck(unit(0, "cm") |> convertX("snpc") |> convertX("cm"),
+          unit(0, "cm"))
+unitCheck(unit(0, "npc") |> convertHeight("snpc") |> convertHeight("npc"),
+          unit(0, "npc"))
+uw <- try(unit(1, "in") |> convertWidth("snpc"),
+          silent = TRUE)
+stopifnot(inherits(uw, "try-error"))
+uh <- try(unit(1, "in") |> convertHeight("snpc"),
+          silent = TRUE)
+stopifnot(inherits(uh, "try-error"))
+popViewport()