Syphon Filter: Dark Mirror: Make the actor's turn after a scripted move frame rate independent

Part of #22669.

When a scripted move reaches its target, the AI only issues the next command
("face this way") two updates later, so the actor coasts for two frames before
turning. At 60fps that's 33ms: the turn starts further from the target, the slide
carries Gabe out of the 1.0 target radius, the steering seeks the target again and
he spins, ending up with his back to the camera in the Episode 1 Part 1 cutscene.
At 20fps (where the pose matches PSP footage) he coasts for 0.1s.

Hook the steering function to hold the turn rate at zero for the first 0.1s after
arriving, so every frame rate gets the 20fps outcome. Anchor heading measured in
that scene: 60fps -81 (was -150), 30fps -82 (was -116), 20fps -80, 15fps -75.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Core/HLE/ReplaceTables.cpp

@@ -26,6 +26,7 @@
 #include "Common/Log.h"
 #include "Common/Swap.h"
 #include "Core/System.h"
+#include "Core/CoreTiming.h"
 #include "Core/Debugger/Breakpoints.h"
 #include "Core/Debugger/MemBlockInfo.h"
 #include "Core/Debugger/SymbolMap.h"
@@ -1564,6 +1565,53 @@ static int Hook_medievil_projectile_update(MIPSState *mips) {
 	return 0;
 }
 
+// Syphon Filter: Dark Mirror's actor steering (#22669). When a scripted move reaches its target, the
+// actor stops, the AI notices on the next update and only issues the next command (usually "face
+// this way") on the one after, so the actor coasts on for two updates before it turns. The turn
+// curves the slide, and if that carries the actor 1.0 from the target, the steering seeks the
+// target again and the actor spins around. At 60fps it coasts for 33ms, starts turning further from
+// the target, slides out and spins, and Gabe faces the wrong way in the in-mission cutscenes. At
+// 20fps it coasts for 0.1s and the poses match PSP footage, so hold the turn for 0.1s at any rate.
+struct SyphonFilterArrival {
+	u64 startUs;
+	u64 lastUs;
+	bool arrivedThisUpdate;
+};
+static std::unordered_map<u32, SyphonFilterArrival> syphonFilterArrivals;
+
+static int Hook_syphonfilter_steer_arrived(MIPSState *mips) {
+	// Runs on every update the actor is stopped inside the target radius.
+	const u64 now = CoreTiming::GetGlobalTimeUs();
+	auto iter = syphonFilterArrivals.find(mips->r[MIPS_REG_S2]);
+	// Also start over if the entry is stale (a savestate load, or a new actor at the same address).
+	if (iter == syphonFilterArrivals.end() || now - iter->second.lastUs > 200000) {
+		syphonFilterArrivals[mips->r[MIPS_REG_S2]] = { now, now, true };
+		return 0;
+	}
+	iter->second.lastUs = now;
+	iter->second.arrivedThisUpdate = true;
+	return 0;
+}
+
+static int Hook_syphonfilter_steer_turn_rate(MIPSState *mips) {
+	// Hooked where the turn rate (f20) is stored, which every update reaches.
+	auto iter = syphonFilterArrivals.find(mips->r[MIPS_REG_S2]);
+	if (iter == syphonFilterArrivals.end()) {
+		return 0;
+	}
+	SyphonFilterArrival &arrival = iter->second;
+	if (!arrival.arrivedThisUpdate) {
+		syphonFilterArrivals.erase(iter);
+		return 0;
+	}
+	arrival.arrivedThisUpdate = false;
+	// A bit under 0.1s, so that at 20fps the turn still starts on the second update after arriving.
+	if (CoreTiming::GetGlobalTimeUs() - arrival.startUs < 95000) {
+		mips->f[20] = 0.0f;
+	}
+	return 0;
+}
+
 static int Hook_resistance_update_trail(MIPSState *mips) {
 	// The trail adds a node on every update that its emitter's rate allows (one per update at most,
 	// and the explosion debris always allow one), and the effect's clock advances 1/60 per update
@@ -2101,6 +2149,8 @@ static const ReplacementTableEntry entries[] = {
 	{ "syphonfilterls_draw_trail", &Hook_syphonfilterls_draw_trail, 0, REPFLAG_HOOKENTER, 0x198 },
 	{ "zuma_pad_analog", &Hook_zuma_pad_analog, 0, REPFLAG_HOOKENTER, 0x234 },
 	{ "zuma_aim_cursor", &Hook_zuma_aim_cursor, 0, REPFLAG_HOOKENTER, 0x210 },
+	{ "syphonfilter_steer", &Hook_syphonfilter_steer_arrived, 0, REPFLAG_HOOKENTER, 0x13E8 },
+	{ "syphonfilter_steer", &Hook_syphonfilter_steer_turn_rate, 0, REPFLAG_HOOKENTER, 0x1610 },
 	{}
 };
 

Core/MIPS/MIPSAnalyst.cpp

@@ -362,6 +362,7 @@ static const HardHashTableEntry hardcodedHashes[] = {
 	{ 0x9e6e007072b74503, 2028, "syphonfilterls_draw_trail", }, // Syphon Filter: Logan's Shadow (US)
 	{ 0x9f269daa6f0da803, 128, "sceGupScissor", },
 	{ 0x9f7919eeb43982b0, 208, "__fixdfsi", },
+	{ 0xa0ec0ed83a53b883, 7304, "syphonfilter_steer", }, // Syphon Filter: Dark Mirror (US)
 	{ 0xa1c9b0a2c71235bf, 1752, "marvelalliance1_copy" }, // Marvel Ultimate Alliance 1 (EU)
 	{ 0x9b76c7f2a41aa805, 1752, "marvelalliance1_copy" }, // Marvel Ultimate alliance 1 (US)
 	{ 0xa1ca0640f11182e7, 72, "strcspn", },