[dxvk] Add config variables for frame pacing

dxvk.conf

@@ -18,6 +18,51 @@
 # dxgi.enableHDR = True
 
 
+# Frame pacing mode managing CPU-GPU synchronization.
+# Defaults to "low-latency" in the draft-PR for demonstration purposes.
+#
+# "max-frame-latency" provides stable latency in the GPU-limit as long as
+# GPU render times are stable. Latency generally is higher but offers great
+# visual smoothness.
+#
+# "low-latency" provides lower latency in the GPU-limit and can be fine-tuned
+# via dxvk.lowLatencyOffset and dxvk.lowLatencyAllowCpuFramesOverlap.
+#
+# "min-latency" possibly provides the lowest latency (low-latency can be
+# quicker in some situations), and offers less fps in the GPU-limit
+# due to stalling the GPU between frames. Generally not recommended,
+# but helpful to get insights to fine-tune the low-latency mode and
+# possibly is useful for running games in the CPU-limit.
+#
+# "low/min-latency" also supports its own fps-limiting enabled via common
+# variables.
+#
+# Supported values: "max-frame-latency", "low-latency", "min-latency"
+
+# dxvk.framePacing = ""
+
+
+# Allows fine-tuning the low-latency frame pacing mode.
+# Positive values make a frame begin later which might improve responsiveness,
+# although only very slightly, but may be relevant for edge cases.
+# Negative values make a frame begin earlier which might improve fps.
+# Values are given in microseconds. Defaults to 0.
+#
+# Supported values: -10000 to 10000
+
+# dxvk.lowLatencyOffset = 0
+
+
+# Determines whether a frame is allowed to begin before finishing processing
+# the cpu-part of the previous one, when low-latency frame pacing is used.
+# Snappiness may be improved when disallowing overlap. On the other hand, this
+# might also decrease fps in certain cases. Defaults to True.
+#
+# Supported values: True, False
+
+# dxvk.lowLatencyAllowCpuFramesOverlap = True
+
+
 # Expose support for dcomp swap chains with a dummy window.
 #
 # This is not a valid implementation of DirectComposition swapchains,
@@ -104,8 +149,13 @@
 #         The implementation will either use VK_NV_low_latency2 if supported
 #         by the driver, or a custom algorithm.
 # - False: Disable Reflex support as well as built-in latency reduction.
+#         This build defaults to False to enable dxvk.framePacing. You need to
+#         enable Reflex manually (Auto) until we support switching back and
+#         forth between Reflex and the low-latency frame pacing - for example
+#         via the ingame options - and more critically we want to enable
+#         low-latency frame pacing if the game doesn't support Reflex.
   
-# dxvk.latencySleep = Auto
+# dxvk.latencySleep = False
 
 
 # Tolerance for the latency sleep heuristic, in microseconds. Higher values

src/dxvk/dxvk_options.cpp

@@ -12,12 +12,16 @@ namespace dxvk {
     useRawSsbo            = config.getOption<Tristate>("dxvk.useRawSsbo",             Tristate::Auto);
     hud                   = config.getOption<std::string>("dxvk.hud", "");
     tearFree              = config.getOption<Tristate>("dxvk.tearFree",               Tristate::Auto);
-    latencySleep          = config.getOption<Tristate>("dxvk.latencySleep",           Tristate::Auto);
+    latencySleep          = config.getOption<Tristate>("dxvk.latencySleep",           Tristate::False);
     latencyTolerance      = config.getOption<int32_t> ("dxvk.latencyTolerance",       1000);
     disableNvLowLatency2  = config.getOption<Tristate>("dxvk.disableNvLowLatency2",   Tristate::Auto);
     hideIntegratedGraphics = config.getOption<bool>   ("dxvk.hideIntegratedGraphics", false);
     zeroMappedMemory      = config.getOption<bool>    ("dxvk.zeroMappedMemory",       false);
     allowFse              = config.getOption<bool>    ("dxvk.allowFse",               false);
+    framePace             = config.getOption<std::string>("dxvk.framePace",           "");
+    lowLatencyOffset      = config.getOption<int32_t> ("dxvk.lowLatencyOffset",       0);
+    lowLatencyAllowCpuFramesOverlap
+                          = config.getOption<bool>    ("dxvk.lowLatencyAllowCpuFramesOverlap", true);
     deviceFilter          = config.getOption<std::string>("dxvk.deviceFilter",        "");
     tilerMode             = config.getOption<Tristate>("dxvk.tilerMode",              Tristate::Auto);
   }

src/dxvk/dxvk_options.h

@@ -38,7 +38,9 @@ namespace dxvk {
     Tristate tearFree = Tristate::Auto;
 
     /// Enables latency sleep
-    Tristate latencySleep = Tristate::Auto;
+    /// Defaults to false in this build to activate the FramePacer,
+    /// especially for the case when the game doesn't support Reflex
+    Tristate latencySleep = Tristate::False;
 
     /// Latency tolerance, in microseconds
     int32_t latencyTolerance = 0u;
@@ -61,6 +63,18 @@ namespace dxvk {
     /// Whether to enable tiler optimizations
     Tristate tilerMode = Tristate::Auto;
 
+    /// Frame pacing
+    std::string framePace;
+
+    /// A value in microseconds to fine-tune the low-latency frame pacing.
+    /// Positive values make a frame begin later which might improve responsiveness.
+    /// Negative values make a frame begin earlier which might improve fps.
+    int32_t lowLatencyOffset;
+
+    /// Determines whether a frame is allowed to begin before finishing processing
+    /// the cpu-part of the previous one, when low-latency frame pacing is used.
+    bool lowLatencyAllowCpuFramesOverlap;
+
     // Device name
     std::string deviceFilter;
   };