Implement MonitorId::get_hidpi_factor for macOS (rust-windowing#410)

* Implement MonitorId::get_hidpi_factor for macOS

* Added changelog entry

CHANGELOG.md

@@ -1,6 +1,8 @@
 # Unreleased
 
 - Impl `Hash`, `PartialEq`, and `Eq` for `events::ModifiersState`.
+- Implement `MonitorId::get_hidpi_factor` for MacOS.
+- Added method `os::macos::MonitorIdExt::get_nsscreen() -> *mut c_void` that gets a `NSScreen` object matching the monitor ID.
 
 # Version 0.11.1 (2018-02-19)
 

src/os/macos.rs

@@ -86,11 +86,17 @@ impl WindowBuilderExt for WindowBuilder {
 pub trait MonitorIdExt {
     /// Returns the identifier of the monitor for Cocoa.
     fn native_id(&self) -> u32;
+    /// Returns a pointer to the NSScreen representing this monitor.
+    fn get_nsscreen(&self) -> Option<*mut c_void>;
 }
 
 impl MonitorIdExt for MonitorId {
     #[inline]
     fn native_id(&self) -> u32 {
         self.inner.get_native_identifier()
     }
+
+    fn get_nsscreen(&self) -> Option<*mut c_void> {
+        self.inner.get_nsscreen().map(|s| s as *mut c_void)
+    }
 }

src/platform/macos/monitor.rs

@@ -1,6 +1,10 @@
+use cocoa::appkit::NSScreen;
+use cocoa::base::{id, nil};
+use cocoa::foundation::{NSString, NSUInteger};
 use core_graphics::display::{CGDirectDisplayID, CGDisplay};
 use std::collections::VecDeque;
 use super::EventsLoop;
+use super::window::IdRef;
 
 #[derive(Clone)]
 pub struct MonitorId(CGDirectDisplayID);
@@ -51,8 +55,35 @@ impl MonitorId {
         unimplemented!()
     }
 
-    #[inline]
     pub fn get_hidpi_factor(&self) -> f32 {
-        1.0
+        let screen = match self.get_nsscreen() {
+            Some(screen) => screen,
+            None => return 1.0, // default to 1.0 when we can't find the screen
+        };
+
+        unsafe { NSScreen::backingScaleFactor(screen) as f32 }
+    }
+
+    pub(crate) fn get_nsscreen(&self) -> Option<id> {
+        unsafe {
+            let native_id = self.get_native_identifier();
+            let screens = NSScreen::screens(nil);
+            let count: NSUInteger = msg_send![screens, count];
+            let key = IdRef::new(NSString::alloc(nil).init_str("NSScreenNumber"));
+            let mut matching_screen: Option<id> = None;
+            for i in 0..count {
+                let screen = msg_send![screens, objectAtIndex: i as NSUInteger];
+                let device_description = NSScreen::deviceDescription(screen);
+                let value: id = msg_send![device_description, objectForKey:*key];
+                if value != nil {
+                    let screen_number: NSUInteger = msg_send![value, unsignedIntegerValue];
+                    if screen_number as u32 == native_id {
+                        matching_screen = Some(screen);
+                        break;
+                    }
+                }
+            }
+            matching_screen
+        }
     }
 }

src/platform/macos/window.rs

@@ -12,7 +12,7 @@ use objc::declare::ClassDecl;
 
 use cocoa;
 use cocoa::base::{id, nil};
-use cocoa::foundation::{NSPoint, NSRect, NSSize, NSString, NSUInteger};
+use cocoa::foundation::{NSPoint, NSRect, NSSize, NSString};
 use cocoa::appkit::{self, NSApplication, NSColor, NSView, NSWindow, NSWindowStyleMask};
 
 use core_graphics::display::CGDisplay;
@@ -389,27 +389,8 @@ impl Window2 {
         unsafe {
             let screen = match attrs.fullscreen {
                 Some(ref monitor_id) => {
-                    let native_id = monitor_id.inner.get_native_identifier();
-                    let matching_screen = {
-                        let screens = appkit::NSScreen::screens(nil);
-                        let count: NSUInteger = msg_send![screens, count];
-                        let key = IdRef::new(NSString::alloc(nil).init_str("NSScreenNumber"));
-                        let mut matching_screen: Option<id> = None;
-                        for i in 0..count {
-                            let screen = msg_send![screens, objectAtIndex:i as NSUInteger];
-                            let device_description = appkit::NSScreen::deviceDescription(screen);
-                            let value: id = msg_send![device_description, objectForKey:*key];
-                            if value != nil {
-                                let screen_number: NSUInteger = msg_send![value, unsignedIntegerValue];
-                                if screen_number as u32 == native_id {
-                                    matching_screen = Some(screen);
-                                    break;
-                                }
-                            }
-                        }
-                        matching_screen
-                    };
-                    Some(matching_screen.unwrap_or(appkit::NSScreen::mainScreen(nil)))
+                    let monitor_screen = monitor_id.inner.get_nsscreen();
+                    Some(monitor_screen.unwrap_or(appkit::NSScreen::mainScreen(nil)))
                 },
                 _ => None,
             };
@@ -729,19 +710,19 @@ unsafe fn nswindow_set_max_dimensions<V: NSWindow + Copy>(
 pub struct IdRef(id);
 
 impl IdRef {
-    fn new(i: id) -> IdRef {
+    pub fn new(i: id) -> IdRef {
         IdRef(i)
     }
 
     #[allow(dead_code)]
-    fn retain(i: id) -> IdRef {
+    pub fn retain(i: id) -> IdRef {
         if i != nil {
             let _: id = unsafe { msg_send![i, retain] };
         }
         IdRef(i)
     }
 
-    fn non_nil(self) -> Option<IdRef> {
+    pub fn non_nil(self) -> Option<IdRef> {
         if self.0 == nil { None } else { Some(self) }
     }
 }