From 8a45801199a869e9f98de47be3962b2f05f50e31 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philip=20Dub=C3=A9?=
 <159546+serprex@users.noreply.github.com>
Date: Sun, 12 Jul 2026 04:01:51 +0000
Subject: [PATCH] optimize frame interpolation memory (#6901)

don't generate all matrices for game tick upfront, interpolate per frame
---
 soh/soh/OTRGlobals.cpp | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/soh/soh/OTRGlobals.cpp b/soh/soh/OTRGlobals.cpp
index 410936f315..2069d4c4c3 100644
--- a/soh/soh/OTRGlobals.cpp
+++ b/soh/soh/OTRGlobals.cpp
@@ -1771,7 +1771,8 @@ extern "C" void Graph_StartFrame() {
 #endif
 }
 
-void RunCommands(Gfx* Commands, const std::vector<std::unordered_map<Mtx*, MtxF>>& mtx_replacements) {
+// Interpolated frames of a tick are evenly spaced numerators time+step, time+2*step, ... over denom.
+void RunCommands(Gfx* Commands, int time, int step, int denom, int count) {
     auto wnd = std::dynamic_pointer_cast<Fast::Fast3dWindow>(OTRGlobals::Instance->context->GetWindow());
 
     if (wnd == nullptr) {
@@ -1787,8 +1788,11 @@ void RunCommands(Gfx* Commands, const std::vector<std::unordered_map<Mtx*, MtxF>
     UIWidgets::Colors themeColor =
         static_cast<UIWidgets::Colors>(CVarGetInteger(CVAR_SETTING("Menu.Theme"), UIWidgets::Colors::LightBlue));
     ImGui::PushStyleColor(ImGuiCol_TitleBgActive, UIWidgets::ColorValues.at(themeColor));
-    for (const auto& m : mtx_replacements) {
-        wnd->DrawAndRunGraphicsCommands(Commands, m);
+    for (int i = 0; i < count; i++) {
+        time += step;
+        std::unordered_map<Mtx*, MtxF> mtx_replacements =
+            (time == denom) ? std::unordered_map<Mtx*, MtxF>() : FrameInterpolation_Interpolate((float)time / denom);
+        wnd->DrawAndRunGraphicsCommands(Commands, mtx_replacements);
         intp->mInterpolationIndex++;
     }
     ImGui::PopStyleColor();
@@ -1802,7 +1806,6 @@ extern "C" void Graph_ProcessGfxCommands(Gfx* commands) {
     }
 
     audio.cv_to_thread.notify_one();
-    std::vector<std::unordered_map<Mtx*, MtxF>> mtx_replacements;
     int target_fps = OTRGlobals::Instance->GetInterpolationFPS();
     static int last_fps;
     static int last_update_rate;
@@ -1822,13 +1825,11 @@ extern "C" void Graph_ProcessGfxCommands(Gfx* commands) {
     // time_base = fps * original_fps (one second)
     int next_original_frame = fps;
 
+    int start_time = time;
+    int count = 0;
     while (time + original_fps <= next_original_frame) {
         time += original_fps;
-        if (time != next_original_frame) {
-            mtx_replacements.push_back(FrameInterpolation_Interpolate((float)time / next_original_frame));
-        } else {
-            mtx_replacements.emplace_back();
-        }
+        count++;
     }
 
     time -= fps;
@@ -1837,13 +1838,15 @@ extern "C" void Graph_ProcessGfxCommands(Gfx* commands) {
         wnd->SetTargetFps(fps);
     }
 
+    int step = original_fps;
     // When the gfx debugger is active, only run with the final mtx
     if (GfxDebuggerIsDebugging()) {
-        mtx_replacements.clear();
-        mtx_replacements.emplace_back();
+        start_time = next_original_frame;
+        step = 0;
+        count = 1;
     }
 
-    RunCommands(commands, mtx_replacements);
+    RunCommands(commands, start_time, step, next_original_frame, count);
 
     last_fps = fps;
     last_update_rate = R_UPDATE_RATE;