Changed the Mac CPTGraphHostingView so it can act as either a layer h…

…osting view or a layer backed view as required. Fixed issue #167.

framework/MacOnly/CPTGraphHostingView.m

@@ -74,12 +74,18 @@ -(instancetype)initWithFrame:(NSRect)frame
         locationInWindow = NSZeroPoint;
         scrollOffset     = CGPointZero;
 
-        CPTLayer *mainLayer = [[CPTLayer alloc] initWithFrame:NSRectToCGRect(frame)];
-        self.layer = mainLayer;
+        if ( !self.superview.wantsLayer ) {
+            self.layer = [self makeBackingLayer];
+        }
     }
     return self;
 }
 
+-(CALayer *)makeBackingLayer
+{
+    return [[CPTLayer alloc] initWithFrame:NSRectToCGRect(self.bounds)];
+}
+
 -(void)dealloc
 {
     [[NSNotificationCenter defaultCenter] removeObserver:self];
@@ -189,6 +195,13 @@ -(void)drawRect:(NSRect)dirtyRect
     }
 }
 
+/// @endcond
+
+#pragma mark -
+#pragma mark Printing
+
+/// @cond
+
 -(BOOL)knowsPageRange:(NSRangePointer)rangePointer
 {
     rangePointer->location = 1;
@@ -477,6 +490,22 @@ -(void)plotAreaBoundsChanged
     [self.window invalidateCursorRectsForView:self];
 }
 
+-(void)viewWillMoveToSuperview:(NSView *)newSuperview
+{
+    if ( self.superview.wantsLayer != newSuperview.wantsLayer ) {
+        self.wantsLayer = NO;
+        self.layer      = nil;
+
+        if ( newSuperview.wantsLayer ) {
+            self.wantsLayer = YES;
+        }
+        else {
+            self.layer      = [self makeBackingLayer];
+            self.wantsLayer = YES;
+        }
+    }
+}
+
 /// @endcond
 
 #pragma mark -