From 233e2f8ced97588b96e76b4e794cf4057dcc7b10 Mon Sep 17 00:00:00 2001
From: Swung0x48 <swung0x48@outlook.com>
Date: Fri, 2 Oct 2026 16:27:16 -0400
Subject: [PATCH] [Fix] (Espryt): swap a pbuffer without damage rectangles

---
 MobileGL/MG_Backend/DirectGLES/DirectGLES.cpp | 19 ++++++++++++-------
 MobileGL/MG_Test/Util/DamageTest.cpp          | 15 +++++++++++++++
 MobileGL/MG_Util/Damage/Damage.h              |  9 +++++++++
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/MobileGL/MG_Backend/DirectGLES/DirectGLES.cpp b/MobileGL/MG_Backend/DirectGLES/DirectGLES.cpp
index 748bbada..9e6bf53c 100644
--- a/MobileGL/MG_Backend/DirectGLES/DirectGLES.cpp
+++ b/MobileGL/MG_Backend/DirectGLES/DirectGLES.cpp
@@ -18159,21 +18159,26 @@ namespace MobileGL::MG_Backend::DirectGLES {
         //
         // The damage is the client's, from the present record (CurrentPresentDamage): GL window
         // coordinates, which is what the native call takes. Whole surface = no rectangles.
-        const EGLSurface drawSurface = ActiveNativeSession().Draw;
+        //
+        // ONLY A WINDOW SURFACE TAKES RECTANGLES: the platform's swap-with-damage hands them to the
+        // surface's native window, and a pbuffer has none (Android's dereferences it regardless).
+        NativeSessionState& session = ActiveNativeSession(); // before the lock: it takes it too
+        const EGLSurface drawSurface = session.Draw;
+        Bool windowSurface = false;
+        if (drawSurface != EGL_NO_SURFACE) {
+            const std::lock_guard<std::mutex> lock(g_nativeRegistryMutex);
+            if (const auto* entry = FindSessionSurfaceLocked(session, drawSurface))
+                windowSurface = entry->Window != static_cast<NativeWindowType>(0);
+        }
         if (g_EGLFuncs.eglSwapBuffersWithDamageEXT != nullptr) {
             const MG_Util::Damage::Region& damage = MG_Backend::CurrentPresentDamage();
             EGLint rects[MG_Util::Damage::kMaxRects * 4] = {};
-            EGLint count = 0;
-            if (!damage.IsFull() && !damage.IsEmpty()) {
-                count = static_cast<EGLint>(MG_Util::Damage::PackRects(damage, rects, MG_Util::Damage::kMaxRects));
-            }
+            const EGLint count = static_cast<EGLint>(MG_Util::Damage::NativeSwapRects(windowSurface, damage, rects));
             g_EGLFuncs.eglSwapBuffersWithDamageEXT(g_Display, drawSurface, count > 0 ? rects : nullptr, count);
         } else {
             g_EGLFuncs.eglSwapBuffers(g_Display, drawSurface);
         }
         if (drawSurface != EGL_NO_SURFACE) {
-            // Resolved before the lock: ActiveNativeSession takes it too.
-            NativeSessionState& session = ActiveNativeSession();
             const std::lock_guard<std::mutex> lock(g_nativeRegistryMutex);
             if (auto* entry = FindSessionSurfaceLocked(session, drawSurface)) ++entry->Presents;
         }
diff --git a/MobileGL/MG_Test/Util/DamageTest.cpp b/MobileGL/MG_Test/Util/DamageTest.cpp
index 2c07ee4c..a97c6a86 100644
--- a/MobileGL/MG_Test/Util/DamageTest.cpp
+++ b/MobileGL/MG_Test/Util/DamageTest.cpp
@@ -137,6 +137,21 @@ TEST(Damage, PackedRectsRoundTripThroughARecord) {
     EXPECT_EQ(Region::FromEglRects(out, 1), Of({{1, 2, 56, 66}}));
 }
 
+// The native swap gets rectangles only for a window surface: Android's swap-with-damage on a
+// pbuffer (a client window's drawable) dereferences the native window it does not have.
+TEST(Damage, OnlyAWindowSurfaceSwapsWithRectangles) {
+    Int32 out[kMaxRects * 4] = {};
+    const Region partial = Of({{10, 20, 30, 40}});
+    EXPECT_EQ(NativeSwapRects(false, partial, out), 0u) << "a pbuffer swaps plainly";
+    EXPECT_EQ(NativeSwapRects(true, Region::Full(), out), 0u);
+    EXPECT_EQ(NativeSwapRects(true, Region(), out), 0u) << "nothing damaged has no rectangle spelling";
+    ASSERT_EQ(NativeSwapRects(true, partial, out), 1u);
+    EXPECT_EQ(out[0], 10);
+    EXPECT_EQ(out[1], 20);
+    EXPECT_EQ(out[2], 30);
+    EXPECT_EQ(out[3], 40);
+}
+
 // Three shared images rotate; each write must bring over what that image missed.
 TEST(Damage, EachBufferCopiesTheDamageItMissedSinceItsLastWrite) {
     constexpr Int32 W = 200, H = 100;
diff --git a/MobileGL/MG_Util/Damage/Damage.h b/MobileGL/MG_Util/Damage/Damage.h
index 10d99678..546141c5 100644
--- a/MobileGL/MG_Util/Damage/Damage.h
+++ b/MobileGL/MG_Util/Damage/Damage.h
@@ -266,6 +266,15 @@ namespace MobileGL::MG_Util::Damage {
         return static_cast<Uint32>(rects.size());
     }
 
+    // The rectangles a native swap-with-damage gets for `damage` (into `out`, room for kMaxRects),
+    // and their count; 0 = a plain swap. Only a window surface takes any: the platform hands them to
+    // the surface's native window, and a pbuffer has none (Android's EGL dereferences it anyway).
+    // An empty damage has no spelling (no rectangles means the whole surface), so it swaps plainly.
+    inline Uint32 NativeSwapRects(Bool windowSurface, const Region& damage, Int32* out) {
+        if (!windowSurface || damage.IsFull() || damage.IsEmpty()) return 0;
+        return PackRects(damage, out, kMaxRects);
+    }
+
     // Per buffer of a rotating set: the damage each has missed since it was last written.
     class BufferDamageTracker {
     public: