app_server: allow disabling affine transforms in DrawState

* New method DrawState::SetTransformEnabled allows to temporarily
  disable all BAffineTransforms in the state stack (up to 'this').
  Later, the same method can be used to reenable the transforms.

  Needed for layers support: when drawing the finished layer bitmap
  onto the view, the affine transforms must not be applied again --
  they have already been applied while drawing the bitmap's contents.

src/servers/app/DrawState.cpp

@@ -370,6 +370,22 @@ DrawState::SetTransform(BAffineTransform transform)
 }
 
 
+/* Can be used to temporarily disable all BAffineTransforms in the state
+   stack, and later reenable them.
+*/
+void
+DrawState::SetTransformEnabled(bool enabled)
+{
+	if (enabled) {
+		BAffineTransform temp = fTransform;
+		SetTransform(BAffineTransform());
+		SetTransform(temp);
+	}
+	else
+		fCombinedTransform = BAffineTransform();
+}
+
+
 DrawState*
 DrawState::Squash()
 {

src/servers/app/DrawState.h

@@ -68,6 +68,7 @@ public:
 								{ return fTransform; }
 		BAffineTransform	CombinedTransform() const
 								{ return fCombinedTransform; }
+		void				SetTransformEnabled(bool enabled);
 
 		DrawState*			Squash();