[idd] config: support fractional refresh rates

Store refresh rates in millihertz and preserve three decimal places.

Advertise exact rational rates while accepting legacy integer values.

Accept rates from 23.900 through 1000.000 Hz.

idd/LGIdd/CIndirectDeviceContext.cpp

@@ -185,20 +185,20 @@ bool CIndirectDeviceContext::PopulateDefaultModes()
     if (!GetResolutionMemoryRequirements(configuredMode.width,
         configuredMode.height, alignment, frameSize, requiredIVSHMEMSize))
     {
-      DEBUG_WARN("Filtering invalid %s mode %ux%u@%u",
+      DEBUG_WARN("Filtering invalid %s mode %ux%u@%.3f",
         configuredMode.extraMode ? "extra" : "configured",
         configuredMode.width, configuredMode.height,
-        configuredMode.refresh);
+        configuredMode.refreshMilliHz / 1000.0);
       continue;
     }
 
     if (requiredIVSHMEMSize > m_ivshmem.GetSize())
     {
       DEBUG_WARN(
-        "Filtering %s mode %ux%u@%u: requires %llu bytes of IVSHMEM, only %llu bytes are available",
+        "Filtering %s mode %ux%u@%.3f: requires %llu bytes of IVSHMEM, only %llu bytes are available",
         configuredMode.extraMode ? "extra" : "configured",
         configuredMode.width, configuredMode.height,
-        configuredMode.refresh,
+        configuredMode.refreshMilliHz / 1000.0,
         (unsigned long long)requiredIVSHMEMSize,
         (unsigned long long)m_ivshmem.GetSize());
       continue;
@@ -644,10 +644,11 @@ void CIndirectDeviceContext::ReloadSettings()
   CSettings::DisplayMode extraMode;
   if (g_settings.GetExtraMode(extraMode))
   {
-    const unsigned refresh = g_settings.GetDefaultRefresh();
-    if (extraMode.refresh != refresh)
+    const unsigned refreshMilliHz =
+      g_settings.GetDefaultRefreshMilliHz();
+    if (extraMode.refreshMilliHz != refreshMilliHz)
     {
-      extraMode.refresh = refresh;
+      extraMode.refreshMilliHz = refreshMilliHz;
       if (!g_settings.SetExtraMode(extraMode))
       {
         ReleaseSRWLockExclusive(&m_modeReloadLock);
@@ -743,7 +744,38 @@ void CIndirectDeviceContext::OnSwapChainReady()
   if (replug)
     m_replugQueued.store(1);
   else if (doSetMode)
-    g_pipe.SetDisplayMode(mode.width, mode.height, mode.refresh);
+    g_pipe.SetDisplayMode(
+      mode.width, mode.height, mode.refreshMilliHz);
+}
+
+static UINT64 GreatestCommonDivisor(UINT64 a, UINT64 b)
+{
+  while (b)
+  {
+    const UINT64 remainder = a % b;
+    a = b;
+    b = remainder;
+  }
+  return a;
+}
+
+static void SetSignalRate(DISPLAYCONFIG_RATIONAL& rate,
+  UINT64 numerator, UINT32 denominator)
+{
+  const UINT64 divisor = GreatestCommonDivisor(numerator, denominator);
+  numerator   /= divisor;
+  denominator /= (UINT32)divisor;
+
+  if (numerator <= UINT32_MAX)
+  {
+    rate.Numerator   = (UINT32)numerator;
+    rate.Denominator = denominator;
+    return;
+  }
+
+  rate.Numerator   =
+    (UINT32)((numerator + denominator / 2) / denominator);
+  rate.Denominator = 1;
 }
 
 static inline void FillSignalInfo(DISPLAYCONFIG_VIDEO_SIGNAL_INFO& signal,
@@ -761,10 +793,9 @@ static inline void FillSignalInfo(DISPLAYCONFIG_VIDEO_SIGNAL_INFO& signal,
   signal.AdditionalSignalInfo.vSyncFreqDivider = monitorMode ? 0 : 1;
   signal.AdditionalSignalInfo.videoStandard    = 255;
 
-  signal.vSyncFreq.Numerator   = mode.refresh;
-  signal.vSyncFreq.Denominator = 1;
-  signal.hSyncFreq.Numerator   = mode.refresh * signal.totalSize.cy;
-  signal.hSyncFreq.Denominator = 1;
+  SetSignalRate(signal.vSyncFreq, mode.refreshMilliHz, 1000);
+  SetSignalRate(signal.hSyncFreq,
+    (UINT64)mode.refreshMilliHz * signal.totalSize.cy, 1000);
 
   signal.scanLineOrdering = DISPLAYCONFIG_SCANLINE_ORDERING_PROGRESSIVE;
   signal.pixelRate        = timing.pixelClock;
@@ -964,10 +995,10 @@ void CIndirectDeviceContext::SetResolution(uint32_t width, uint32_t height)
   }
 
   CSettings::DisplayMode mode = {};
-  mode.width     = width;
-  mode.height    = height;
-  mode.refresh   = g_settings.GetDefaultRefresh();
-  mode.preferred = true;
+  mode.width          = width;
+  mode.height         = height;
+  mode.refreshMilliHz = g_settings.GetDefaultRefreshMilliHz();
+  mode.preferred      = true;
 
   bool modesLoaded = false;
   AcquireSRWLockExclusive(&m_modeReloadLock);