DRMBackend: Cache requested dynamic refresh rate and compare against …

…that

Otherwise 51Hz -> 51.60Hz does not compare back to 51Hz, as it rounds to 52Hz.

Closes: ValveSoftware#1398

src/Backends/DRMBackend.cpp

@@ -2952,6 +2952,8 @@ bool drm_update_color_mgmt(struct drm_t *drm)
 	return true;
 }
 
+int g_nDynamicRefreshHz = 0;
+
 static void drm_unset_mode( struct drm_t *drm )
 {
 	drm->pending.mode_id = 0;
@@ -2967,6 +2969,7 @@ static void drm_unset_mode( struct drm_t *drm )
 	g_nOutputRefresh = drm->preferred_refresh;
 	if (g_nOutputRefresh == 0)
 		g_nOutputRefresh = gamescope::ConvertHztomHz( 60 );
+	g_nDynamicRefreshHz = 0;
 
 	g_bRotated = false;
 }
@@ -2982,6 +2985,7 @@ bool drm_set_mode( struct drm_t *drm, const drmModeModeInfo *mode )
 	drm->needs_modeset = true;
 
 	g_nOutputRefresh = gamescope::GetModeRefresh( mode );
+	g_nDynamicRefreshHz = 0;
 
 	update_drm_effective_orientations(drm, mode);
 
@@ -3044,7 +3048,13 @@ bool drm_set_refresh( struct drm_t *drm, int refresh )
 
 	mode.type = DRM_MODE_TYPE_USERDEF;
 
-	return drm_set_mode(drm, &mode);
+	bool bSuccess = drm_set_mode(drm, &mode);
+	if ( !bSuccess )
+		return false;
+
+	g_nDynamicRefreshHz = refresh;
+
+	return true;
 }
 
 bool drm_set_resolution( struct drm_t *drm, int width, int height )

src/steamcompmgr.cpp

@@ -143,6 +143,8 @@ gamescope_color_mgmt_luts g_ScreenshotColorMgmtLutsHDR[ EOTF_Count ];
 static lut1d_t g_tmpLut1d;
 static lut3d_t g_tmpLut3d;
 
+extern int g_nDynamicRefreshHz;
+
 bool g_bForceHDRSupportDebug = false;
 extern float g_flInternalDisplayBrightnessNits;
 extern float g_flHDRItmSdrNits;
@@ -2482,11 +2484,15 @@ paint_all(bool async)
 
 		uint64_t now = get_time_in_nanos();
 
-		// Compare in Hz, as the actual resulting clocks from the mode generation
-		// may give us eg. 90'004 vs 90'000
-		int32_t nOutputRefreshHz = gamescope::ConvertmHzToHz( g_nOutputRefresh );
+		// The actual output hz generated by the mode, could be off by one either side, due to rounding.
+		//
+		// Check what we cached for the current dynamic refresh Hz we put in -- otherwise, convert
+		// g_nOutputRefresh -> Hz rounded.
+		int32_t nCurrentDynamicOutputHz = g_nDynamicRefreshHz
+			? g_nDynamicRefreshHz
+			: gamescope::ConvertmHzToHz( g_nOutputRefresh );
 
-		if ( nOutputRefreshHz == nTargetRefreshHz )
+		if ( nCurrentDynamicOutputHz == nTargetRefreshHz )
 		{
 			g_uDynamicRefreshEqualityTime = now;
 		}