mangoapp: show the panel's measured refresh rate from gamescope

src/app/main.cpp

@@ -412,6 +412,9 @@ static void msg_read_thread(){
                     if (msg_bytes > offsetof(mangoapp_msg_v1, latency_ns))
                         gamescope_frametime(mangoapp_v1->app_frametime_ns, mangoapp_v1->latency_ns);
 
+                    if (msg_bytes > offsetof(mangoapp_msg_v1, scanoutRefreshmHz))
+                        HUDElements.scanout_refresh = mangoapp_v1->scanoutRefreshmHz / 1000.f;
+
                     if (should_new_frame)
                     {
                         {

src/app/mangoapp_proto.h

@@ -23,6 +23,7 @@ struct mangoapp_msg_v1 {
     char engineName[40];
     uint8_t upscaler; // mangoapp_upscaler that produced the frame, LINEAR for none
     uint8_t wantedUpscaler; // mangoapp_upscaler the user selected
+    uint32_t scanoutRefreshmHz; // refreshes the panel actually scanned out, follows VRR, 0 when unknown
     // WARNING: Always ADD fields, never remove or repurpose fields
 } __attribute__((packed));
 

src/hud_elements.cpp

@@ -1700,12 +1700,16 @@ void HudElements::hdr() {
 }
 
 void HudElements::refresh_rate() {
-    if (HUDElements.refresh > 0) {
+    if (HUDElements.refresh > 0 || HUDElements.scanout_refresh > 0) {
         ImGui::PushFont(HUDElements.sw_stats->font_secondary);
         ImguiNextColumnFirstItem();
         HUDElements.TextColored(HUDElements.colors.engine, "%s", "Display Hz");
         ImguiNextColumnOrNewRow();
-        right_aligned_text(HUDElements.colors.text, HUDElements.ralign_width, "%i", HUDElements.refresh);
+        // gamescope measures the panel's real rate, which VRR moves away from the mode's.
+        if (HUDElements.scanout_refresh > 0)
+            right_aligned_text(HUDElements.colors.text, HUDElements.ralign_width, "%.1f", HUDElements.scanout_refresh);
+        else
+            right_aligned_text(HUDElements.colors.text, HUDElements.ralign_width, "%i", HUDElements.refresh);
         ImGui::PopFont();
     }
 }

src/hud_elements.h

@@ -58,6 +58,7 @@ class HudElements{
         uint32_t vendorID;
         int hdr_status = 0;
         int refresh = 0;
+        float scanout_refresh = 0.f;
         unsigned int vsync = 10;
 
         enum display_servers {