vulkan: Add a throttler before present for precise frame rates.

gtk/CMakeLists.txt

@@ -126,6 +126,8 @@ if(USE_SLANG)
                         ../vulkan/vulkan_shader_chain.hpp
                         ../vulkan/vulkan_simple_output.hpp
                         ../vulkan/vulkan_simple_output.cpp
+                        ../vulkan/std_chrono_throttle.cpp
+                        ../vulkan/std_chrono_throttle.hpp
                         src/gtk_display_driver_vulkan.cpp
                         src/gtk_display_driver_vulkan.h)
 

gtk/src/gtk_display_driver_vulkan.cpp

@@ -92,6 +92,7 @@ int S9xVulkanDisplayDriver::init()
         else
         {
             window->enable_widget("shader_parameters_item", true);
+
             return 0;
         }
     }
@@ -117,21 +118,21 @@ void S9xVulkanDisplayDriver::update(uint16_t *buffer, int width, int height, int
     if (!context)
         return;
 
-    if (gui_config->reduce_input_lag)
-        context->wait_idle();
-
     auto viewport = S9xApplyAspect(width, height, current_width, current_height);
+    context->swapchain->set_max_frame_rate(60.09881389744051);
 
     if (shaderchain)
     {
         shaderchain->do_frame((uint8_t *)buffer, width, height, stride_in_pixels << 1, vk::Format::eR5G6B5UnormPack16, viewport.x, viewport.y, viewport.w, viewport.h);
-        return;
     }
     else if (simple_output)
     {
         simple_output->set_filter(Settings.BilinearFilter);
         simple_output->do_frame((uint8_t *)buffer, width, height, stride_in_pixels << 1, viewport.x, viewport.y, viewport.w, viewport.h);
     }
+
+    if (gui_config->reduce_input_lag)
+       context->wait_idle();
 }
 
 int S9xVulkanDisplayDriver::query_availability()

vulkan/std_chrono_throttle.cpp

@@ -0,0 +1,37 @@
+#include "std_chrono_throttle.hpp"
+#include <thread>
+
+using namespace std::chrono;
+
+void Throttle::set_frame_rate(double frame_rate)
+{
+    max_frame_rate = frame_rate;
+    frame_duration = 1.0 / max_frame_rate;
+    frame_duration_us = microseconds(int64_t(frame_duration * 1000000.0));
+}
+
+microseconds Throttle::remaining()
+{
+    auto now = time_point_cast<microseconds>(steady_clock::now());
+    auto diff = (now - then);
+    return frame_duration_us - diff;
+}
+
+void Throttle::wait_for_frame()
+{
+    auto time_to_wait = remaining();
+
+    if (time_to_wait.count() > 0)
+        std::this_thread::sleep_for(time_to_wait);
+}
+
+void Throttle::advance()
+{
+    then += frame_duration_us;
+}
+
+void Throttle::reset()
+{
+    auto now = time_point_cast<microseconds>(steady_clock::now());
+    then = now;
+}

vulkan/std_chrono_throttle.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <chrono>
+
+struct Throttle
+{
+    void set_frame_rate(double frame_rate);
+    void advance();
+    void reset();
+    void wait_for_frame();
+    std::chrono::microseconds remaining();
+    double max_frame_rate = 0.0;
+    double frame_duration = 0.0;
+    std::chrono::microseconds frame_duration_us;
+    std::chrono::time_point<std::chrono::steady_clock, std::chrono::microseconds> then;
+};

vulkan/vulkan_swapchain.cpp

@@ -1,5 +1,6 @@
 #include "vulkan_swapchain.hpp"
 #include "vulkan/vulkan_structs.hpp"
+#include <thread>
 
 namespace Vulkan
 {
@@ -230,6 +231,11 @@ bool Swapchain::begin_frame()
     return true;
 }
 
+void Swapchain::set_max_frame_rate(double frame_rate)
+{
+    throttle.set_frame_rate(frame_rate);
+}
+
 bool Swapchain::end_frame()
 {
     auto &frame = frames[current_frame];
@@ -249,6 +255,19 @@ bool Swapchain::end_frame()
         .setSwapchains(swapchain_object.get())
         .setImageIndices(current_swapchain_image);
 
+    if (throttle.max_frame_rate != 0.0)
+    {
+        auto remaining = throttle.remaining();
+        if (remaining < -throttle.frame_duration_us / 10)
+            throttle.reset();
+        else if (remaining.count() > 0)
+        {
+            queue.waitIdle();
+            throttle.wait_for_frame();
+            throttle.advance();
+        }
+    }
+
     auto result = queue.presentKHR(present_info);
 
     current_frame = (current_frame + 1) % max_latency;

vulkan/vulkan_swapchain.hpp

@@ -3,7 +3,7 @@
 #include "vulkan/vulkan.hpp"
 #include "vulkan/vulkan_handles.hpp"
 #include "vulkan/vulkan_structs.hpp"
-#include <deque>
+#include "std_chrono_throttle.hpp"
 
 namespace Vulkan
 {
@@ -28,6 +28,7 @@ class Swapchain
     bool end_frame();
     // Returns true if vsync setting was changed, false if it was the same
     bool set_vsync(bool on);
+    void set_max_frame_rate(double frame_rate);
 
     vk::Image get_image();
     vk::Framebuffer get_framebuffer();
@@ -61,6 +62,7 @@ class Swapchain
 
     vk::UniqueRenderPass render_pass;
 
+    Throttle throttle;
     unsigned int current_frame = 0;
     unsigned int current_swapchain_image = 0;
     unsigned int num_swapchain_images = 0;

win32/snes9xw.vcxproj

@@ -449,6 +449,7 @@
     <ClInclude Include="..\vulkan\vulkan_slang_pipeline.hpp" />
     <ClInclude Include="..\vulkan\vulkan_swapchain.hpp" />
     <ClInclude Include="..\vulkan\vulkan_texture.hpp" />
+    <ClInclude Include="..\vulkan\std_chrono_throttle.hpp" />
     <ClInclude Include="AVIOutput.h" />
     <ClInclude Include="CCGShader.h" />
     <ClInclude Include="CD3DCG.h" />
@@ -612,6 +613,7 @@
     <ClCompile Include="..\vulkan\vulkan_slang_pipeline.cpp" />
     <ClCompile Include="..\vulkan\vulkan_swapchain.cpp" />
     <ClCompile Include="..\vulkan\vulkan_texture.cpp" />
+    <ClCompile Include="..\vulkan\std_chrono_throttle.cpp" />
     <ClCompile Include="AVIOutput.cpp" />
     <ClCompile Include="CCGShader.cpp" />
     <ClCompile Include="CD3DCG.cpp" />