From 10eaf402783467311cfc55ff7a79a443a1394ada Mon Sep 17 00:00:00 2001
From: Kurt Kartaltepe <kkartaltepe@gmail.com>
Date: Sun, 19 Dec 2021 20:34:19 -0800
Subject: [PATCH] hud: Modify histogram to use buckets and report p50/p90/p99

This makes the histogram option behave like a histogram instead of
simply rendering the same data as frame_timing without the histogram
option.

This is mostly for reference and personal use as is and does not match
some of the repo's coding standards.
---
 src/hud_elements.cpp | 38 +++++++++++++++++++++++++++++++++++---
 src/overlay.cpp      | 12 ++++++++++++
 src/overlay.h        |  3 ++-
 3 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/src/hud_elements.cpp b/src/hud_elements.cpp
index 6ba6f9733b..a795249046 100644
--- a/src/hud_elements.cpp
+++ b/src/hud_elements.cpp
@@ -537,9 +537,41 @@ void HudElements::frame_timing(){
         double min_time = 0.0f;
         double max_time = 50.0f;
         if (HUDElements.params->enabled[OVERLAY_PARAM_ENABLED_histogram]){
-            ImGui::PlotHistogram(hash, get_time_stat, HUDElements.sw_stats,
-                                ARRAY_SIZE(HUDElements.sw_stats->frames_stats), 0,
-                                NULL, min_time, max_time,
+            float *ft = HUDElements.sw_stats->frame_times;
+            size_t ft_size = ARRAY_SIZE(HUDElements.sw_stats->frame_times);
+            uint32_t tsmin=0, tsmax=0;
+            uint32_t p50=0, p90=0, p99=0;
+            // one frame latency between this and update_hud_info_with_frametime.
+            // That makes p99 only kick in after 100 frames.
+            uint32_t frame_count =  std::min((size_t)HUDElements.sw_stats->n_frames, ARRAY_SIZE(HUDElements.sw_stats->frames_stats));
+            uint32_t frames_seen = 0;
+            uint32_t height = 0;
+            for(uint32_t i = 0; i < ft_size; i++) {
+                frames_seen += ft[i];
+                if(ft[i] > height) { height = ft[i]; }
+                if(tsmin == 0 && ft[i] > 0) { tsmin = i; }
+                if(i > tsmax && ft[i] > 0) { tsmax = i; }
+                if(p50 == 0 && frames_seen >= frame_count/2) {
+                    p50 = i;
+                }
+                if(p90 == 0 && frames_seen >= frame_count - (frame_count/10)) {
+                    p90 = i;
+                }
+                if(p99 == 0 && frames_seen >= frame_count - (frame_count/100)) {
+                    p99 = i;
+                }
+            }
+            ImGui::PushFont(HUDElements.sw_stats->font1);
+            ImGui::TextColored(HUDElements.colors.text, "p50/p90/p99");
+            ImGui::TextColored(HUDElements.colors.text, "%3d/%3d/%3d ms", p50, p90, p99);
+            // ImGui::TextColored(HUDElements.colors.text, "s:%d,c:%d,h:%d", frames_seen, frame_count, height);
+            ImGui::TextColored(HUDElements.colors.text, "min:%d,max:%d", tsmin, tsmax);
+            ImGui::PopFont();
+            ImGui::TableNextRow(); ImGui::TableNextColumn();
+            // Draw at least 16 buckets.
+            ImGui::PlotHistogram(hash, ft,
+                                std::max(tsmax, 16u), tsmin,
+                                NULL, 0, height,
                                 ImVec2(ImGui::GetContentRegionAvailWidth() * HUDElements.params->table_columns, 50));
         } else {
             ImGui::PlotLines(hash, get_time_stat, HUDElements.sw_stats,
diff --git a/src/overlay.cpp b/src/overlay.cpp
index 91ca33dc4d..22ff5641b0 100644
--- a/src/overlay.cpp
+++ b/src/overlay.cpp
@@ -170,6 +170,18 @@ void update_hud_info_with_frametime(struct swapchain_stats& sw_stats, struct ove
    if (sw_stats.last_present_time) {
         sw_stats.frames_stats[f_idx].stats[OVERLAY_PLOTS_frame_timing] =
             frametime_ns;
+        uint32_t frametime_ms = frametime_ns/1000000;
+        if (frametime_ms < 1000) {
+            sw_stats.frame_times[frametime_ms] += 1.0;
+        }
+        // keep the histogram for the same window as the normal frame graph.
+        if (sw_stats.n_frames >= ARRAY_SIZE(sw_stats.frames_stats)) {
+            uint32_t fp_idx = (sw_stats.n_frames + 1) % ARRAY_SIZE(sw_stats.frames_stats);
+            uint32_t oldest_frametime_ms = sw_stats.frames_stats[fp_idx].stats[OVERLAY_PLOTS_frame_timing]/1000000;
+            if(oldest_frametime_ms < 1000) {
+                sw_stats.frame_times[oldest_frametime_ms] -= 1.0;
+            }
+        }
    }
 
    frametime = frametime_ns / 1000;
diff --git a/src/overlay.h b/src/overlay.h
index 18b839a27a..3192441180 100644
--- a/src/overlay.h
+++ b/src/overlay.h
@@ -51,6 +51,7 @@ struct swapchain_stats {
    double time_dividor;
    struct frame_stat stats_min, stats_max;
    struct frame_stat frames_stats[200];
+   float frame_times[1000]; // histogram buckets.
 
    ImFont* font1 = nullptr;
    ImFont* font_text = nullptr;
@@ -167,4 +168,4 @@ extern void process_control_socket(struct instance_data *instance_data);
 void render_mpris_metadata(overlay_params& params, mutexed_metadata& meta, uint64_t frame_timing);
 #endif
 
-#endif //MANGOHUD_OVERLAY_H
\ No newline at end of file
+#endif //MANGOHUD_OVERLAY_H