Affine transforms: add method to test for dilation

* Add IsDilation() to BAffineTransform and Transformable which check
  whether the transform is a dilation, i.e. consists of only
  translation and/or scaling

headers/os/interface/AffineTransform.h

@@ -171,6 +171,8 @@ public:
 										= kDefaultEpsilon) const;
 			bool					IsIdentity(double epsilon
 										= kDefaultEpsilon) const;
+			bool					IsDilation(double epsilon
+										= kDefaultEpsilon) const;
 			bool					IsEqual(const BAffineTransform& other,
 										double epsilon
 											= kDefaultEpsilon) const;

src/kits/interface/AffineTransform.cpp

@@ -513,6 +513,14 @@ BAffineTransform::IsIdentity(double epsilon) const
 }
 
 
+bool
+BAffineTransform::IsDilation(double epsilon) const
+{
+	return IsEqualEpsilon(shy, 0.0, epsilon)
+		&& IsEqualEpsilon(shx, 0.0, epsilon);
+}
+
+
 bool
 BAffineTransform::IsEqual(const BAffineTransform& other, double epsilon) const
 {

src/servers/app/drawing/Painter/Transformable.cpp

@@ -169,6 +169,15 @@ Transformable::IsIdentity() const
 }
 
 
+bool
+Transformable::IsDilation() const
+{
+	double m[6];
+	store_to(m);
+	return m[1] == 0.0 && m[2] == 0.0;
+}
+
+
 void
 Transformable::Transform(double* x, double* y) const
 {

src/servers/app/drawing/Painter/Transformable.h

@@ -38,6 +38,7 @@ class Transformable : public BArchivable,
 			void				Reset();
 
 			bool				IsIdentity() const;
+			bool				IsDilation() const;
 //			bool				operator==(const Transformable& other) const;
 //			bool				operator!=(const Transformable& other) const;