nx2:vi2: report the display's maximum buffer resolution

Command 106 was auto-stubbed, and Fire Emblem: Fortune's Weave treats
its empty reply as mode 0 and picks its 720p tier (rendering at 360p).
Report mode 4 (1440p) docked and 2 (1080p, the screen) handheld; the
game then renders at 720p and 540p and upscales to those.
EDEN_VI2_MAX_RESOLUTION_MODE overrides the mode.

Assisted-by: Claude Opus 5.5 (debugging, implementation and drafting)
Signed-off-by: Duck912 <350528965+Duck912@users.noreply.github.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/core/hle/service/nx2_gsv.h b/src/core/hle/service/nx2_gsv.h
index 397e2aacb8..5a2963f179 100644
--- a/src/core/hle/service/nx2_gsv.h
+++ b/src/core/hle/service/nx2_gsv.h
@@ -1454,6 +1454,7 @@ public:
             // auto stub's empty success reply works, but logged two lines per call (a 50 MB log
             // in an 18 minute session).
             {105, &INx2Vi2Session::SucceedQuietly, "Unknown105 (display \"default\")"},
+            {106, &INx2Vi2Session::GetBufferMaxResolution, "GetBufferMaxResolution"},
             {228, &INx2Vi2Session::CancelClientBuffer, "CancelClientBuffer"},
             {229, &INx2Vi2Session::PresentClientBuffer, "PresentClientBuffer"},
         });
@@ -1847,6 +1848,29 @@ private:
         rb.Push<u32>(0);
     }
 
+    // The highest buffer resolution mode of the "default" display. Fire Emblem: Fortune's Weave picks
+    // its output from it: 1 -> 1280x720, 2 -> 1920x1080, 4 and 8 -> 2560x1440; 0 (the auto stub's
+    // reply), 3 and 5 fall back to 720p. Docked reports 4, handheld 2 (the screen is 1080p);
+    // EDEN_VI2_MAX_RESOLUTION_MODE=<n> overrides.
+    void GetBufferMaxResolution(HLERequestContext& ctx) {
+        const auto* packet = ctx.CommandBuffer();
+        const u64 name = u64{packet[2]} | (u64{packet[3]} << 32);
+        constexpr u64 DefaultDisplay = 0x00746c7561666564ULL; // "default"
+        Result result = Kernel::ResultInvalidCombination;
+        u64 mode{};
+        if (packet[0] == 0x7a && packet[1] == 2) {
+            result = Result{ErrorModule::VI, 7};
+            if (name == DefaultDisplay) {
+                static const char* forced = std::getenv("EDEN_VI2_MAX_RESOLUTION_MODE");
+                mode = forced ? std::strtoull(forced, nullptr, 0) : Settings::IsDockedMode() ? 4 : 2;
+                result = ResultSuccess;
+            }
+        }
+        IPC::ResponseBuilder rb{ctx, 4};
+        rb.Push(result.raw);
+        rb.Push(mode);
+    }
+
     // The same reply as the auto stub (success, no data), without its log lines.
     void SucceedQuietly(HLERequestContext& ctx) {
         IPC::ResponseBuilder rb{ctx, 2};