Debugger: Fix the Win32 VFPU window at high DPI, implement it in ImDebugger

- Fixes #21636

The Win32 window drew with a fixed 12px font and hardcoded pixel offsets, so at
high DPI the grid ran under the (dialog-unit sized) tab bar. It now uses the
DPI-scaled debugger font, derives the layout from its metrics and the tab bar's
position, and sizes the window to fit. The HalfFloat, Bytes, Shorts and Ints
tabs, which used to show floats, now work.

The ImDebugger VFPU window, which was a TODO, shows the same grid and modes,
with changed values highlighted.

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

UI/ImDebugger/ImDebugger.cpp

@@ -26,6 +26,7 @@
 #include "Core/Debugger/Breakpoints.h"
 #include "Core/MIPS/MIPSDebugInterface.h"
 #include "Core/MIPS/MIPSTables.h"
+#include "Core/MIPS/MIPSVFPUUtils.h"
 #include "Core/HW/SimpleAudioDec.h"
 #include "Core/FileSystems/MetaFileSystem.h"
 #include "Core/Debugger/SymbolMap.h"
@@ -354,12 +355,68 @@ static void DrawFPRs(ImConfig &config, ImControl &control, const MIPSDebugInterf
 }
 
 static void DrawVFPU(ImConfig &config, ImControl &control, const MIPSDebugInterface *mipsDebug, const ImSnapshotState &prev) {
-	ImGui::SetNextWindowSize(ImVec2(320, 600), ImGuiCond_FirstUseEver);
+	ImGui::SetNextWindowSize(ImVec2(520, 600), ImGuiCond_FirstUseEver);
 	if (!ImGui::Begin("VFPU", &config.vfpuOpen)) {
 		ImGui::End();
 		return;
 	}
-	ImGui::Text("TODO");
+	const bool appearing = ImGui::IsWindowAppearing();
+	if (ImGui::BeginTabBar("vfpuMode")) {
+		for (int i = 0; i < (int)VFPUDisplayMode::COUNT; i++) {
+			// Restore the saved mode when the window appears.
+			ImGuiTabItemFlags flags = (appearing && i == config.vfpuDisplayMode) ? ImGuiTabItemFlags_SetSelected : 0;
+			if (ImGui::BeginTabItem(g_vfpuDisplayModeNames[i], nullptr, flags)) {
+				config.vfpuDisplayMode = i;
+				ImGui::EndTabItem();
+			}
+		}
+		ImGui::EndTabBar();
+	}
+
+	bool noDiff = coreState == CORE_RUNNING_CPU || coreState == CORE_STEPPING_GE;
+	const VFPUDisplayMode mode = (VFPUDisplayMode)config.vfpuDisplayMode;
+
+	// Laid out like the Win32 VFPU window: each column of a matrix is a row vector (Rmnr), each line a
+	// column vector (Cmc0).
+	ImGui::BeginChild("vfpuMatrices");
+	char temp[64];
+	for (int matrix = 0; matrix < 8; matrix++) {
+		ImGui::PushID(matrix);
+		if (ImGui::BeginTable("matrix", 5, ImGuiTableFlags_Borders | ImGuiTableFlags_SizingFixedFit)) {
+			snprintf(temp, sizeof(temp), "M%d00", matrix);
+			ImGui::TableSetupColumn(temp);
+			for (int column = 0; column < 4; column++) {
+				snprintf(temp, sizeof(temp), "R%d0%d", matrix, column);
+				ImGui::TableSetupColumn(temp, ImGuiTableColumnFlags_WidthFixed, ImGui::CalcTextSize("-0000.000000").x);
+			}
+			ImGui::TableHeadersRow();
+
+			for (int row = 0; row < 4; row++) {
+				ImGui::TableNextRow();
+				ImGui::TableNextColumn();
+				ImGui::Text("C%d%d0", matrix, row);
+				for (int column = 0; column < 4; column++) {
+					ImGui::TableNextColumn();
+					int index = column * 32 + row + matrix * 4;
+					u32 value = mipsDebug->GetRegValue(2, index);
+					// NOTE: Using memcmp to avoid NaN problems.
+					bool diff = memcmp(&value, &prev.vpr[voffset[index]], 4) != 0 && !noDiff;
+					if (diff) {
+						ImGui::PushStyleColor(ImGuiCol_Text, ImDebuggerColor_Diff);
+					}
+					FormatVFPUValue(temp, sizeof(temp), value, mode);
+					ImGui::TextUnformatted(temp);
+					if (diff) {
+						ImGui::PopStyleColor();
+					}
+				}
+			}
+			ImGui::EndTable();
+		}
+		ImGui::PopID();
+		ImGui::Spacing();
+	}
+	ImGui::EndChild();
 	ImGui::End();
 }
 
@@ -3117,6 +3174,7 @@ void ImConfig::SyncConfig(IniFile *ini, bool save) {
 	sync.Sync("gprOpen", &gprOpen, false);
 	sync.Sync("fprOpen", &fprOpen, false);
 	sync.Sync("vfpuOpen", &vfpuOpen, false);
+	sync.Sync("vfpuDisplayMode", &vfpuDisplayMode, 0);
 	sync.Sync("threadsOpen", &threadsOpen, false);
 	sync.Sync("callstackOpen", &callstackOpen, false);
 	sync.Sync("breakpointsOpen", &breakpointsOpen, false);