Add missing functions regarding display refresh rate

Cargo.toml

@@ -17,11 +17,15 @@ objc = "0.2.5"
 core-foundation-sys = "0.6.2"
 metal = { version = "0.14.0", features = ["private"] }
 
+[dependencies.core-graphics]
+version = "0.17.3"
+optional = true
+
 [features]
 default = [ "display_link", ]
 all = [ "display_link", "direct3d", "io_suface", "opengl" ]
 
-display_link = [ "opengl", ]
+display_link = [ "opengl", "core-graphics" ]
 direct3d  = [ ]
 io_suface = [ ]
 opengl    = [ ]

src/display_link.rs

@@ -1,5 +1,16 @@
-use crate::core_foundation_sys::base::CFTypeID;
+use crate::{
+    core_foundation_sys::base::CFTypeID,
+    core_graphics::display::CGDirectDisplayID,
+    CVReturn, CVTime,
+};
+
+#[derive(Debug, Copy, Clone)]
+pub enum __CVDisplayLink { }
+pub type CVDisplayLinkRef = *mut __CVDisplayLink;
 
 extern "C" {
     pub fn CVDisplayLinkGetTypeID() -> CFTypeID;
-}
+    pub fn CVDisplayLinkCreateWithCGDisplay(displayID: CGDirectDisplayID, displayLinkOut: *mut CVDisplayLinkRef) -> CVReturn;
+    pub fn CVDisplayLinkGetNominalOutputVideoRefreshPeriod(displayLink: CVDisplayLinkRef) -> CVTime;
+    pub fn CVDisplayLinkRelease(displayLink: CVDisplayLinkRef);
+}

src/lib.rs

@@ -43,6 +43,8 @@ pub use self::metal_texture_cache::*;
 
 cfg_if! {
     if #[cfg(feature = "display_link")] {
+        extern crate core_graphics;
+
         pub mod host_time;
         pub mod display_link;