1 files changed, 12 insertions, 0 deletions
diff --git a/gfx/thebes/gfxMatrix.h b/gfx/thebes/gfxMatrix.h
index 9282a22db..4f92262cc 100644
--- a/gfx/thebes/gfxMatrix.h
+++ b/gfx/thebes/gfxMatrix.h
@@ -112,6 +112,18 @@ public:
               _31 == 0.0 && _32 == 0.0;
     }
 
+    /* Returns true if the matrix is a rectilinear transformation (i.e.
+     * grid-aligned rectangles are transformed to grid-aligned rectangles)
+     */
+    bool IsRectilinear() const {
+      if (FuzzyEqual(_12, 0) && FuzzyEqual(_21, 0)) {
+        return true;
+      } else if (FuzzyEqual(_22, 0) && FuzzyEqual(_11, 0)) {
+        return true;
+      }
+      return false;
+    }
+
     /**
      * Inverts this matrix, if possible. Otherwise, the matrix is left
      * unchanged.