SCI32: Add reg_t comparisons for graphics sorting

2 files changed, 26 insertions, 0 deletions

diff --git a/engines/sci/engine/vm_types.cpp b/engines/sci/engine/vm_types.cpp
index 53a5a5c507..00a67fc9cc 100644
--- a/engines/sci/engine/vm_types.cpp
+++ b/engines/sci/engine/vm_types.cpp
@@ -230,6 +230,10 @@ int reg_t::cmp(const reg_t right, bool treatAsUnsigned) const {
 			return toUint16() - right.toUint16();
 		else
 			return toSint16() - right.toSint16();
+#ifdef ENABLE_SCI32
+	} else if (getSciVersion() >= SCI_VERSION_2) {
+		return sci32Comparison(right);
+#endif
 	} else if (pointerComparisonWithInteger(right)) {
 		return 1;
 	} else if (right.pointerComparisonWithInteger(*this)) {
@@ -238,6 +242,24 @@ int reg_t::cmp(const reg_t right, bool treatAsUnsigned) const {
 		return lookForWorkaround(right, "comparison").toSint16();
 }
 
+int reg_t::sci32Comparison(const reg_t right) const {
+	// In SCI32, MemIDs are normally indexes into the memory manager's handle
+	// list, but the engine reserves indexes at and above 20000 for objects
+	// that were created inside the engine (as opposed to inside the VM). The
+	// engine compares these as a tiebreaker for graphics objects that are at
+	// the same priority, and it is necessary to at least minimally handle
+	// this situation.
+	// This is obviously a bogus comparision, but then, this entire thing is
+	// bogus. For the moment, it just needs to be deterministic.
+	if (isNumber() && !right.isNumber()) {
+		return 1;
+	} else if (right.isNumber() && !isNumber()) {
+		return -1;
+	}
+
+	return getOffset() - right.getOffset();
+}
+
 bool reg_t::pointerComparisonWithInteger(const reg_t right) const {
 	// This function handles the case where a script tries to compare a pointer
 	// to a number. Normally, we would not want to allow that. However, SCI0 -
diff --git a/engines/sci/engine/vm_types.h b/engines/sci/engine/vm_types.h
index a646478a8e..e60f52e85c 100644
--- a/engines/sci/engine/vm_types.h
+++ b/engines/sci/engine/vm_types.h
@@ -160,6 +160,10 @@ private:
 	int cmp(const reg_t right, bool treatAsUnsigned) const;
 	reg_t lookForWorkaround(const reg_t right, const char *operation) const;
 	bool pointerComparisonWithInteger(const reg_t right) const;
+
+#ifdef ENABLE_SCI32
+	int sci32Comparison(const reg_t right) const;
+#endif
 };
 
 static inline reg_t make_reg(SegmentId segment, uint16 offset) {