Merge pull request #5314 from JonRC/fix/eps-gcheck-simple-objects

Fix #5312: EPS files written by Ghostscript's eps2write open

contributors/people.toml

@@ -189,3 +189,7 @@ sync_github_name = false
 [people.WadahBadawi]
 display_name = "Wadah Badawi"
 sync_github_name = true
+
+[people.JonRC]
+real_name = "Jonathan Cardoso"
+display_name = "Jonathan Cardoso"

crates/eps/src/import/interp.rs

@@ -1135,9 +1135,12 @@ impl<'a> Interp<'a> {
             PdfMark => {
                 self.pop_to_mark()?;
             }
+            // True for a simple object, and for a composite one in global VM (PLRM 3rd ed., `gcheck`);
+            // every composite here is in local VM. Procsets that copy values into global VM leave
+            // alone those whose `gcheck` is true, such as a halftone's numbers.
             Gcheck | Scheck => {
-                self.pop()?;
-                self.push(Obj::Bool(false))?;
+                let simple = !self.pop()?.is_composite();
+                self.push(Obj::Bool(simple))?;
             }
             CurrentShared => self.push(Obj::Bool(false))?,
             SetShared | SetVmThreshold | VmReclaim | Echo => {

crates/eps/src/import/obj.rs

@@ -286,6 +286,11 @@ impl Obj {
             Self::GState(_) => "gstatetype",
         }
     }
+
+    /// A composite object, whose value lives in VM; the others are simple (PLRM 3rd ed., §3.3.1).
+    pub fn is_composite(&self) -> bool {
+        matches!(self, Self::Str(_) | Self::ExecStr(_) | Self::Array { .. } | Self::Dict(_) | Self::File { .. } | Self::Save(_) | Self::GState(_))
+    }
 }
 
 /// The values of a string or an array: a run of storage that other strings or arrays may share

crates/eps/src/import/tests_generators.rs

@@ -592,6 +592,21 @@ showpage"##;
     assert!(near(bounds(&meshes[1]), Rect::new(150.0, 90.0, 190.0, 140.0)), "{:?}", bounds(&meshes[1]));
 }
 
+/// Ghostscript 9's `eps2write` copies the initial graphics state (`currenthalftone`,
+/// `currentcolortransfer`) into global VM before it draws, with a copier for each composite type.
+/// It copies only what `gcheck` says is in local VM: `gcheck` is true for every simple object
+/// (PLRM 3rd ed., `gcheck`), so the halftone's numbers stay as they are. Written from the PLRM.
+#[test]
+fn gcheck_is_true_for_simple_objects() {
+    super::tests::check("1 gcheck 2.5 gcheck and /n gcheck and true gcheck and null gcheck and /add load gcheck and mark gcheck and");
+    super::tests::check("(s) gcheck not 1 dict gcheck not and {} gcheck not and 1 scheck and (s) scheck not and");
+    super::tests::check(
+        "/copiers << /dicttype { << exch { cp2g } forall >> } /arraytype { [ exch { cp2g } forall ] } >> def \
+         /cp2g { dup gcheck not { copiers 1 index type get exec } if } bind def \
+         currenthalftone cp2g /Frequency get 60 eq [ currentcolortransfer ] cp2g length 4 eq and",
+    );
+}
+
 /// A procset written as the PostScript Language Reference (3rd ed.) describes the Level 2 and 3
 /// facilities programs probe before drawing: a resource category made from `Generic` and
 /// resources defined and found in it (§3.9), local and global VM (`currentglobal`, `setglobal`,