USB: Follow the PCRTC video mode for GunCon2 aim

The per-serial calibration table is applied once by AutoConfigure() and
never revisited, but its values are video mode dependent -- the table
carries commented-out 480i/480p twins for three discs to prove it.

Time Crisis 2 and 3 halve the vertical mode when entering split-screen
co-op (640x448 -> 640x224). The range of positions the gun can report
halves with it while the frozen scale keeps sending the full range, so
aim travels twice as far as it should.

Scale the vertical deflection by the ratio between the live PCRTC
resolution and the one latched on first use. The ratio is exactly 1.0
for a game that never changes mode, so output is unchanged everywhere
else, and the correction is only armed when a table row actually
matched -- manually configured guns and unlisted games are untouched.

Only the vertical is corrected. The horizontal reading also moves when
one of the two display circuits is disabled (Time Crisis 3 reports
320x224 for several frames while transitioning), which is a change in
what is being composited rather than in video timing.

The ratio is clamped so it can only reduce the deflection. The
reference is not saved to the state, so a state made in split-screen
latches the reduced height on load; the clamp keeps that inert rather
than letting it overshoot by 2x when the game returns to full height.

Author: dyzt

pcsx2/GS/GS.cpp

@@ -662,6 +662,21 @@ void GSgetInternalResolution(int* width, int* height)
 	*height = res.y;
 }
 
+void GSgetDisplayResolution(int* width, int* height)
+{
+	GSRenderer* gs = g_gs_renderer.get();
+	if (!gs)
+	{
+		*width = 0;
+		*height = 0;
+		return;
+	}
+
+	const GSVector2i res(gs->PCRTCDisplays.GetResolution());
+	*width = res.x;
+	*height = res.y;
+}
+
 void GSgetStats(SmallStringBase& info)
 {
 	GSPerfMon& pm = g_perfmon;

pcsx2/GS/GS.h

@@ -96,6 +96,7 @@ std::vector<GSAdapterInfo> GSGetAdapterInfo(GSRendererType renderer);
 u32 GSGetMaxUpscaleMultiplier(u32 max_texture_size);
 GSVideoMode GSgetDisplayMode();
 void GSgetInternalResolution(int* width, int* height);
+void GSgetDisplayResolution(int* width, int* height);
 void GSgetStats(SmallStringBase& info);
 void GSgetMemoryStats(SmallStringBase& info);
 void GSgetTitleStats(std::string& info);

pcsx2/USB/usb-lightgun/guncon2.cpp

@@ -149,6 +149,12 @@ namespace usb_lightgun
 		u32 cursor_color = 0xFFFFFFFF;
 		float relative_pos[4] = {};
 
+		bool follow_video_mode = false;
+		s32 ref_width = 0;
+		s32 ref_height = 0;
+		s32 last_width = 0;
+		s32 last_height = 0;
+
 		//////////////////////////////////////////////////////////////////////////
 		// Device State (Saved)
 		//////////////////////////////////////////////////////////////////////////
@@ -362,6 +368,7 @@ namespace usb_lightgun
 			center_y = static_cast<float>(gc.center_y);
 			screen_width = gc.screen_width;
 			screen_height = gc.screen_height;
+			follow_video_mode = true;
 			return;
 		}
 
@@ -392,6 +399,33 @@ namespace usb_lightgun
 			fx *= scale_x;
 			fy *= scale_y;
 
+			if (follow_video_mode)
+			{
+				int cur_width, cur_height;
+				GSgetDisplayResolution(&cur_width, &cur_height);
+				if (cur_height > 0)
+				{
+					if (ref_height == 0)
+					{
+						ref_width = cur_width;
+						ref_height = cur_height;
+					}
+
+					const float mode_scale =
+						std::min(1.0f, static_cast<float>(cur_height) / static_cast<float>(ref_height));
+
+					if (cur_width != last_width || cur_height != last_height)
+					{
+						last_width = cur_width;
+						last_height = cur_height;
+						Console.WriteLn(fmt::format("(GunCon2) Display {}x{} (reference {}x{}), scaling vertical aim by {:.3f}",
+							cur_width, cur_height, ref_width, ref_height, mode_scale));
+					}
+
+					fy *= mode_scale;
+				}
+			}
+
 			// and re-center based on game center
 			s32 x = static_cast<s32>(std::round(fx + center_x));
 			s32 y = static_cast<s32>(std::round(fy + center_y));