unify screen calculations.

native/Avalonia.Native/src/OSX/Screens.mm

@@ -5,12 +5,6 @@ class Screens : public ComSingleObject<IAvnScreens, &IID_IAvnScreens>
     public:
     FORWARD_IUNKNOWN()
     
-    private:
-    CGFloat PrimaryDisplayHeight()
-    {
-      return NSMaxY([[[NSScreen screens] firstObject] frame]);
-    }
-    
 public:
     virtual HRESULT GetScreenCount (int* ret) override
     {
@@ -36,12 +30,12 @@ public:
             ret->Bounds.Height = [screen frame].size.height;
             ret->Bounds.Width = [screen frame].size.width;
             ret->Bounds.X = [screen frame].origin.x;
-            ret->Bounds.Y = PrimaryDisplayHeight() - [screen frame].origin.y - ret->Bounds.Height;
+            ret->Bounds.Y = ConvertPointY(ToAvnPoint([screen frame].origin)).Y - ret->Bounds.Height;
             
             ret->WorkingArea.Height = [screen visibleFrame].size.height;
             ret->WorkingArea.Width = [screen visibleFrame].size.width;
             ret->WorkingArea.X = [screen visibleFrame].origin.x;
-            ret->WorkingArea.Y = PrimaryDisplayHeight() - [screen visibleFrame].origin.y - ret->WorkingArea.Height;
+            ret->WorkingArea.Y = ConvertPointY(ToAvnPoint([screen visibleFrame].origin)).Y - ret->WorkingArea.Height;
             
             ret->PixelDensity = [screen backingScaleFactor];
             

native/Avalonia.Native/src/OSX/common.h

@@ -34,6 +34,7 @@ extern NSApplicationActivationPolicy AvnDesiredActivationPolicy;
 extern NSPoint ToNSPoint (AvnPoint p);
 extern AvnPoint ToAvnPoint (NSPoint p);
 extern AvnPoint ConvertPointY (AvnPoint p);
+extern CGFloat PrimaryDisplayHeight();
 extern NSSize ToNSSize (AvnSize s);
 #ifdef DEBUG
 #define NSDebugLog(...) NSLog(__VA_ARGS__)

native/Avalonia.Native/src/OSX/main.mm

@@ -299,10 +299,14 @@ AvnPoint ToAvnPoint (NSPoint p)
 
 AvnPoint ConvertPointY (AvnPoint p)
 {
-    auto sw = [NSScreen.screens objectAtIndex:0].frame;
+    auto primaryDisplayHeight = NSMaxY([[[NSScreen screens] firstObject] frame]);
     
-    auto t = MAX(sw.origin.y, sw.origin.y + sw.size.height);
-    p.Y = t - p.Y;
+    p.Y = primaryDisplayHeight - p.Y;
     
     return p;
 }
+
+CGFloat PrimaryDisplayHeight()
+{
+  return NSMaxY([[[NSScreen screens] firstObject] frame]);
+}