1 files changed, 94 insertions, 0 deletions
diff --git a/third_party/rust/wgpu-hal/src/auxil/dxgi/time.rs b/third_party/rust/wgpu-hal/src/auxil/dxgi/time.rs
new file mode 100644
index 0000000000..fd99c097d7
--- /dev/null
+++ b/third_party/rust/wgpu-hal/src/auxil/dxgi/time.rs
@@ -0,0 +1,94 @@
+#![allow(dead_code)] // IPresentationManager is unused currently
+
+use std::mem;
+
+use winapi::um::{
+    profileapi::{QueryPerformanceCounter, QueryPerformanceFrequency},
+    winnt::LARGE_INTEGER,
+};
+
+pub enum PresentationTimer {
+    /// DXGI uses QueryPerformanceCounter
+    Dxgi {
+        /// How many ticks of QPC per second
+        frequency: u64,
+    },
+    /// IPresentationManager uses QueryInterruptTimePrecise
+    #[allow(non_snake_case)]
+    IPresentationManager {
+        fnQueryInterruptTimePrecise: unsafe extern "system" fn(*mut winapi::ctypes::c_ulonglong),
+    },
+}
+
+impl std::fmt::Debug for PresentationTimer {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match *self {
+            Self::Dxgi { frequency } => f
+                .debug_struct("DXGI")
+                .field("frequency", &frequency)
+                .finish(),
+            Self::IPresentationManager {
+                fnQueryInterruptTimePrecise,
+            } => f
+                .debug_struct("IPresentationManager")
+                .field(
+                    "QueryInterruptTimePrecise",
+                    &(fnQueryInterruptTimePrecise as usize),
+                )
+                .finish(),
+        }
+    }
+}
+
+impl PresentationTimer {
+    /// Create a presentation timer using QueryPerformanceFrequency (what DXGI uses for presentation times)
+    pub fn new_dxgi() -> Self {
+        let mut frequency: LARGE_INTEGER = unsafe { mem::zeroed() };
+        let success = unsafe { QueryPerformanceFrequency(&mut frequency) };
+        assert_ne!(success, 0);
+
+        Self::Dxgi {
+            frequency: unsafe { *frequency.QuadPart() } as u64,
+        }
+    }
+
+    /// Create a presentation timer using QueryInterruptTimePrecise (what IPresentationManager uses for presentation times)
+    ///
+    /// Panics if QueryInterruptTimePrecise isn't found (below Win10)
+    pub fn new_ipresentation_manager() -> Self {
+        // We need to load this explicitly, as QueryInterruptTimePrecise is only available on Windows 10+
+        //
+        // Docs say it's in kernel32.dll, but it's actually in kernelbase.dll.
+        let kernelbase =
+            libloading::os::windows::Library::open_already_loaded("kernelbase.dll").unwrap();
+        // No concerns about lifetimes here as kernelbase is always there.
+        let ptr = unsafe { kernelbase.get(b"QueryInterruptTimePrecise").unwrap() };
+        Self::IPresentationManager {
+            fnQueryInterruptTimePrecise: *ptr,
+        }
+    }
+
+    /// Gets the current time in nanoseconds.
+    pub fn get_timestamp_ns(&self) -> u128 {
+        // Always do u128 math _after_ hitting the timing function.
+        match *self {
+            PresentationTimer::Dxgi { frequency } => {
+                let mut counter: LARGE_INTEGER = unsafe { mem::zeroed() };
+                let success = unsafe { QueryPerformanceCounter(&mut counter) };
+                assert_ne!(success, 0);
+
+                // counter * (1_000_000_000 / freq) but re-ordered to make more precise
+                (unsafe { *counter.QuadPart() } as u128 * 1_000_000_000) / frequency as u128
+            }
+            PresentationTimer::IPresentationManager {
+                fnQueryInterruptTimePrecise,
+            } => {
+                let mut counter = 0;
+                unsafe { fnQueryInterruptTimePrecise(&mut counter) };
+
+                // QueryInterruptTimePrecise uses units of 100ns for its tick.
+                counter as u128 * 100
+            }
+        }
+    }
+}