[Fix] (Pipe): the default framebuffer's record names no placeholder surface that only one share group holds.

MobileGL/MG_Impl/Pipe/FramebufferEmit.h

@@ -524,22 +524,28 @@ namespace MobileGL::MG_Pipe {
             out.Target = static_cast<Uint8>(target);
             out.IsDefault = fbo.IsDefaultFramebuffer() ? 1 : 0;
 
-            // THE COLOUR POINTS. A default framebuffer keeps its one colour surface under
-            // BackLeft rather than under Color0, and the record has exactly one place to put
-            // it: Color[0], which is also the index MGPipeDrawBufferIndex maps that token to,
-            // so the array and the draw-buffer indices agree by construction.
-            if (out.IsDefault != 0) {
-                out.Color[0] = SurfaceOf(fbo, FramebufferAttachmentType::BackLeft);
-            } else {
+            // THE SURFACES - and a DEFAULT framebuffer's record names none. Its storage on the
+            // server is the surface the context is current on (the native window or pbuffer,
+            // Magma's swapchain); both servers answer every default-framebuffer question from
+            // IsDefault and never resolve a surface of this record. The frontend's attachments
+            // are placeholders: one process-wide set of textures every context's framebuffer 0
+            // shares, created once, so their records live in the ONE share group that was
+            // bound when they were born. Naming them here sent every other group a handle it
+            // holds no record for ("texture {12, 0} has no applier resource record" on each of
+            // its draws) and marked bind bits on them under whichever context drew next.
+            // Publishing them into every group instead would build a driver texture per group
+            // for storage nothing reads. The extent still comes from them (FillGeometry), and
+            // the draw-buffer indices below still map BackLeft to slot 0.
+            if (out.IsDefault == 0) {
                 for (SizeT i = 0; i < kMGPipeMaxColorAttachments; ++i) {
                     out.Color[i] = SurfaceOf(fbo, static_cast<FramebufferAttachmentType>(
                                                       static_cast<Int>(FramebufferAttachmentType::Color0) +
                                                       static_cast<Int>(i)));
                 }
+                out.Depth = SurfaceOf(fbo, FramebufferAttachmentType::Depth);
+                out.Stencil = SurfaceOf(fbo, FramebufferAttachmentType::Stencil);
+                out.ReadSurface = SurfaceOf(fbo, fbo.GetReadBuffer());
             }
-            out.Depth = SurfaceOf(fbo, FramebufferAttachmentType::Depth);
-            out.Stencil = SurfaceOf(fbo, FramebufferAttachmentType::Stencil);
-            out.ReadSurface = SurfaceOf(fbo, fbo.GetReadBuffer());
 
             const auto& drawBuffers = fbo.GetDrawBuffers();
             for (SizeT i = 0; i < kMGPipeMaxColorAttachments; ++i) {

MobileGL/MG_Test/Pipe/FramebufferEmitTest.cpp

@@ -245,7 +245,7 @@ TEST(FramebufferEmit, TheEmitterIsOneNeverDestroyedProcessSingleton) {
     X(FramebufferEmit, EveryNonTexturePointCarriesTheUnknownSentinelsRatherThanZero)              \
     X(FramebufferEmit, ADeadFramebuffersNamedRecordLatchIsRetired)                                 \
     X(FramebufferEmit, TheRecordsElevenSurfacesAreTheWholePointSetTheServerReads)                \
-    X(FramebufferEmit, ADefaultFramebufferResizeReEmitsTheRecordWithItsNewExtent)
+    X(FramebufferEmit, ADefaultFramebufferResizeReEmitsTheRecordWithItsNewExtent)                    X(FramebufferEmit, TheDefaultFramebuffersRecordNamesNoSurfaceAShareGroupWouldHaveToHold)
 
 #define MGL_DECLARE_PULL_SKIP(Suite, Name)                                                         \
     TEST(Suite, Name) { GTEST_SKIP() << "compiled only under MOBILEGL_PIPE_PUSH"; }
@@ -706,6 +706,46 @@ TEST(FramebufferEmit, ADefaultFramebufferResizeReEmitsTheRecordWithItsNewExtent)
     EXPECT_EQ(applied->Height, 96u);
 }
 
+// THE DEFAULT FRAMEBUFFER'S RECORD NAMES NO SURFACE. Its attachments are the frontend's
+// placeholders - one process-wide set every context's framebuffer 0 shares, whose records live in
+// the one share group that was bound when they were born - and the server's default framebuffer
+// is the surface the context is current on. Red while the record named them: every other share
+// group was sent texture handles it held no record for, and logged the miss on each draw.
+TEST(FramebufferEmit, TheDefaultFramebuffersRecordNamesNoSurfaceAShareGroupWouldHaveToHold) {
+    FramebufferScope scope;
+    const auto color = MakeColorTexture(96, 64);
+    const auto depthStencil = MakeShared<TextureObject2D>(97);
+    depthStencil->SetInternalFormat(TextureInternalFormat::Depth32FStencil8);
+    depthStencil->AllocateStorage(TextureUploadTarget::Texture2D, 0,
+                                  MipmapInput{IntVec3{64, 64, 1}, static_cast<SizeT>(64 * 64 * 8)});
+    const auto fbo0 = MakeShared<FramebufferObject>(0); // what MG_Impl::BuildDefaultFramebuffer builds
+    ASSERT_TRUE(fbo0->IsDefaultFramebuffer());
+    for (const auto point : {FramebufferAttachmentType::Color0, FramebufferAttachmentType::FrontLeft,
+                             FramebufferAttachmentType::FrontRight, FramebufferAttachmentType::BackLeft,
+                             FramebufferAttachmentType::BackRight}) {
+        fbo0->AttachTexture(point, color, TextureUploadTarget::Texture2D);
+    }
+    fbo0->AttachTexture(FramebufferAttachmentType::Depth, depthStencil, TextureUploadTarget::Texture2D);
+    fbo0->AttachTexture(FramebufferAttachmentType::Stencil, depthStencil, TextureUploadTarget::Texture2D);
+    BindDrawAndRead(fbo0, fbo0);
+    Framebuffers().EmitFramebufferState(Ctx());
+
+    const MGPFramebufferState* const applied = MGPipeApplier().DrawFramebuffer();
+    ASSERT_NE(applied, nullptr) << "the default framebuffer's record did not reach the applier";
+    EXPECT_EQ(applied->IsDefault, 1) << "MGPFramebufferState::IsDefault";
+    for (Uint i = 0; i < kMGPipeMaxColorAttachments; ++i) {
+        EXPECT_EQ(applied->Color[i].Kind, kMGPipeSurfaceKindNone) << "MGPSurface::Kind at colour point " << i;
+        EXPECT_TRUE(MGPipeHandleIsNull(applied->Color[i].Res)) << "MGPSurface::Res at colour point " << i;
+    }
+    EXPECT_EQ(applied->Depth.Kind, kMGPipeSurfaceKindNone) << "MGPSurface::Kind on the depth point";
+    EXPECT_EQ(applied->Stencil.Kind, kMGPipeSurfaceKindNone) << "MGPSurface::Kind on the stencil point";
+    EXPECT_EQ(applied->ReadSurface.Kind, kMGPipeSurfaceKindNone) << "MGPFramebufferState::ReadSurface";
+    // What the record still carries: the extent, and slot 0 as the back buffer's draw buffer.
+    EXPECT_EQ(applied->Width, 64u) << "MGPFramebufferState::Width";
+    EXPECT_EQ(applied->Height, 64u) << "MGPFramebufferState::Height";
+    EXPECT_EQ(applied->DrawBuffers[0], 0) << "MGPFramebufferState::DrawBuffers[0]";
+}
+
 // ============================ D-D2 ============================
 //
 // RED BEFORE THIS PACKAGE LANDED. RenderbufferObject's three storage setters bump no version

MobileGL/MG_Test/Wire/ConcurrentContextsTest.cpp

@@ -454,6 +454,12 @@ namespace {
         ASSERT_EQ(r.initialized, 1) << "the client hung or did not come up; client log " << logBase << "\n"
                                     << server.Log();
         ASSERT_EQ(r.finished, 1) << "the client did not finish";
+        // Every record named something its own context's share group holds. The default
+        // framebuffer's placeholder textures were the standing exception: one process-wide set,
+        // recorded in the group bound when they were born and named by every context's draw.
+        const std::string serverLog = server.Log();
+        EXPECT_EQ(serverLog.find("has no applier resource record"), std::string::npos)
+            << "a record named a texture its share group holds no record for";
         const int threads = shape == Shape::ReadbackRace ? 1 + kRaceChurners : kThreads;
         for (int i = 0; i < threads; ++i) {
             const ThreadReport& t = r.threads[i];