Handle case where there is no window and test that case

Rebel/NSView+RBLAlignmentAdditions.m

@@ -11,10 +11,17 @@
 @implementation NSView (RBLAlignmentAdditions)
 
 - (NSRect)rbl_viewBackingAlignedRect:(NSRect)rect options:(NSAlignmentOptions)options {
-	NSAssert(self.window != nil, @"View must have a window in order to obtain a rectangle aligned to the backing.");
+	if (self.window) {
 		NSRect windowRect = [self convertRect:rect toView:nil];
 		NSRect windowBackingRect = [self backingAlignedRect:windowRect options:options];
 		return [self convertRect:windowBackingRect fromView:nil];
+	} else {
+		CGFloat scaleFactor = [[NSScreen mainScreen] backingScaleFactor];
+		CGAffineTransform transformToBacking = CGAffineTransformMakeScale(scaleFactor, scaleFactor);
+        CGRect backingRect = CGRectApplyAffineTransform(rect, transformToBacking);
+		backingRect = NSIntegralRectWithOptions(backingRect, options);
+		return CGRectApplyAffineTransform(backingRect, CGAffineTransformInvert(transformToBacking));
+	}
 }
 
 @end

RebelTests/NSView+RBLAlignmentAdditionsSpec.m

@@ -9,10 +9,16 @@
 SpecBegin(NSViewRBLAlignmentAdditions)
 
 describe(@"view alignment", ^{
+	__block NSView *view;
+	before(^{
+		 view = [[NSView alloc] initWithFrame:NSMakeRect(20.f, 20.f, 20.f, 20.f)];
+	});
 	it(@"should return a rect aligned to the view backing", ^{
 		NSWindow *window = [[NSWindow alloc] initWithContentRect:NSMakeRect(0.f, 0.f, 100.f, 100.f) styleMask:NSTitledWindowMask | NSClosableWindowMask | NSMiniaturizableWindowMask | NSResizableWindowMask backing:NSBackingStoreBuffered defer:NO];
-		NSView *view = [[NSView alloc] initWithFrame:NSMakeRect(20.f, 20.f, 20.f, 20.f)];
 		[window.contentView addSubview:view];
+	});
+	it(@"should return a rect aligned to the view backing without a window.", ^{});
+	after(^{
 		NSRect nonAlignedRect = NSMakeRect(10.2f, 11.8f, 12.f, 13.f);
 		NSRect alignedRect = [view rbl_viewBackingAlignedRect:nonAlignedRect options:NSAlignAllEdgesNearest];
 		expect(NSEqualRects(alignedRect, NSMakeRect(10.f, 12.f, 12.f, 13.f))).to.beTruthy();