Add tests for checking equivalency of SDL_GetPerformanceCounter() and Stopwatch.GetTimestamp()

SDL3-CS.Tests/TestTimestampSource.cs

@@ -0,0 +1,122 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Diagnostics;
+using NUnit.Framework;
+
+namespace SDL.Tests
+{
+    /// <summary>
+    /// These tests check that <see cref="Stopwatch.GetTimestamp"/> and <see cref="SDL3.SDL_GetPerformanceCounter"/> use the same source of time.
+    /// </summary>
+    /// <remarks>
+    /// You also need to check that the clocks remain consistent even after the system is put to sleep. To do so:
+    /// <list type="number">
+    ///     <item>Run both tests normally.</item>
+    ///     <item>Run the tests one at a time, putting your computer to sleep while the test is running.
+    ///         Adjust <see cref="ITERATIONS"/> and <see cref="SLEEP_TIMEOUT"/> as needed.</item>
+    ///     <item>Run both tests normally. (Checks consistency after a sleep cycle.)</item>
+    /// </list>
+    /// </remarks>
+    public class TestTimestampSource
+    {
+        public const int ITERATIONS = 5;
+        public const int SLEEP_TIMEOUT = 200;
+
+        [OneTimeSetUp]
+        public void OneTimeSetUp()
+        {
+            SDL3.SDL_Init(0);
+        }
+
+        [OneTimeTearDown]
+        public void OneTimeTearDown()
+        {
+            SDL3.SDL_Quit();
+        }
+
+        [Test]
+        public void TestSDLBoundedByStopwatch()
+        {
+            Assert.That(SDL3.SDL_GetPerformanceFrequency(), Is.EqualTo(Stopwatch.Frequency));
+
+            DateTime? wallClockLastEnd = null;
+            long? lastEnd = null;
+
+            for (int i = 0; i < ITERATIONS; i++)
+            {
+                var wallClockStart = DateTime.UtcNow;
+
+                long stopwatchStart = Stopwatch.GetTimestamp();
+                ulong sdlTimestamp = SDL3.SDL_GetPerformanceCounter();
+                long stopwatchEnd = Stopwatch.GetTimestamp();
+
+                var wallClockEnd = DateTime.UtcNow;
+
+                Assert.That(sdlTimestamp, Is.GreaterThanOrEqualTo(stopwatchStart).And.LessThanOrEqualTo(stopwatchEnd));
+
+                if (lastEnd.HasValue && wallClockLastEnd.HasValue)
+                {
+                    long diff = stopwatchStart - lastEnd.Value;
+                    double seconds = (double)diff / Stopwatch.Frequency;
+                    double wallClockSeconds = (wallClockStart - wallClockLastEnd.Value).TotalSeconds;
+                    Console.WriteLine($"Elapsed inter-iteration: {diff} ({seconds} s), wall clock: {wallClockSeconds} s");
+                    Console.WriteLine();
+                }
+
+                Console.WriteLine($"Stw: {stopwatchStart}");
+                Console.WriteLine($"SDL: {sdlTimestamp}");
+                Console.WriteLine($"Stw: {stopwatchEnd}");
+                Console.WriteLine($"Elapsed this interation: {stopwatchEnd - stopwatchStart}");
+                Console.WriteLine();
+
+                lastEnd = stopwatchEnd;
+                wallClockLastEnd = wallClockEnd;
+
+                Thread.Sleep(SLEEP_TIMEOUT);
+            }
+        }
+
+        [Test]
+        public void TestStopwatchBoundedBySDL()
+        {
+            Assert.That(Stopwatch.Frequency, Is.EqualTo(SDL3.SDL_GetPerformanceFrequency()));
+
+            DateTime? wallClockLastEnd = null;
+            ulong? lastEnd = null;
+
+            for (int i = 0; i < ITERATIONS; i++)
+            {
+                var wallClockStart = DateTime.UtcNow;
+
+                ulong sdlStart = SDL3.SDL_GetPerformanceCounter();
+                long stopwatchTimestamp = Stopwatch.GetTimestamp();
+                ulong sdlEnd = SDL3.SDL_GetPerformanceCounter();
+
+                var wallClockEnd = DateTime.UtcNow;
+
+                Assert.That(stopwatchTimestamp, Is.GreaterThanOrEqualTo(sdlStart).And.LessThanOrEqualTo(sdlEnd));
+
+                if (lastEnd.HasValue && wallClockLastEnd.HasValue)
+                {
+                    ulong diff = sdlStart - lastEnd.Value;
+                    double seconds = (double)diff / SDL3.SDL_GetPerformanceFrequency();
+                    double wallClockSeconds = (wallClockStart - wallClockLastEnd.Value).TotalSeconds;
+                    Console.WriteLine($"Elapsed inter-iteration: {diff} ({seconds} s), wall clock: {wallClockSeconds} s");
+                    Console.WriteLine();
+                }
+
+                Console.WriteLine($"SDL: {sdlStart}");
+                Console.WriteLine($"Stw: {stopwatchTimestamp}");
+                Console.WriteLine($"SDL: {sdlEnd}");
+                Console.WriteLine($"Elapsed: {sdlEnd - sdlStart}");
+                Console.WriteLine();
+
+                lastEnd = sdlEnd;
+                wallClockLastEnd = wallClockEnd;
+
+                Thread.Sleep(SLEEP_TIMEOUT);
+            }
+        }
+    }
+}