[Fix] (MG_State, MG_Backend/DirectVulkan): bump the texture bind generation when a context default texture crosses the undefined<->defined boundary so cached sampled sets re-resolve, and collect the fallback texture into the sampled set so its first use transitions outside the render pass

MobileGL/MG_Backend/DirectVulkan/Renderer/UniformManager.cpp

@@ -613,7 +613,15 @@ namespace MobileGL::MG_Backend::DirectVulkan {
 
             MG_State::GLState::ITextureObject* texture = ResolveSamplerTextureRaw(program, programObj, binding);
             if (!texture) {
-                continue;
+                // ResolveSamplerDescriptor will substitute the fallback texture for this binding;
+                // include it in the sampled set so the pre-render-pass sync/transition pass covers
+                // its first use instead of leaving that work to happen inside an active pass.
+                const TextureTarget preferredTarget = programObj.samplerTextureTargetByBinding[binding];
+                if (preferredTarget != TextureTarget::Texture2D &&
+                    preferredTarget != TextureTarget::TextureRectangle) {
+                    continue;
+                }
+                texture = GetFallbackTexture(preferredTarget).get();
             }
 
             auto found = std::find(outTextures.begin(), outTextures.end(), texture);

MobileGL/MG_State/GLState/Core.h

@@ -108,6 +108,7 @@ namespace MobileGL {
                 // texture is bound at a unit; lets a backend skip re-resolving an unchanged
                 // per-draw sampled-texture set.
                 Uint64 GetTextureBindGeneration() const { return m_textureState.GetTextureBindGeneration(); }
+                void BumpTextureBindGeneration() { m_textureState.BumpTextureBindGeneration(); }
                 Bool ValidateTextureName(Uint index) const;
                 Bool ValidateTextureObject(Uint index) const;
                 Int GetActiveTextureUnit() const;

MobileGL/MG_State/GLState/TextureState/TextureObject.cpp

@@ -7,6 +7,7 @@
 // End of Source File Header
 
 #include "TextureObject.h"
+#include "MG_State/GLState/Core.h"
 #include "MG_Util/Types.h"
 #include <MG_Util/Metrics/TextureMetrics.h>
 
@@ -52,6 +53,20 @@ namespace MobileGL {
             void TextureObjectBase::SetInternalFormat(TextureInternalFormat format) {
                 if (format == m_internalFormat) return;
 
+                // A default texture (name 0) changes IsUndefinedDefaultTexture on the
+                // Unknown<->defined transition, which changes per-draw sampled-set membership
+                // without any bind happening; bump the bind generation so cached sampled sets
+                // re-resolve instead of replaying the stale membership. The identity check
+                // excludes the other externalIndex-0 objects (proxy textures, default-FBO
+                // attachments) whose definedness never feeds sampled-set membership, so e.g.
+                // proxy probes cannot churn the cache.
+                if (m_externalIndex == 0 && pGLContext &&
+                    (m_internalFormat == TextureInternalFormat::Unknown) !=
+                        (format == TextureInternalFormat::Unknown) &&
+                    pGLContext->GetDefaultTextureObject(GetTarget()).get() == this) {
+                    pGLContext->BumpTextureBindGeneration();
+                }
+
                 m_internalFormat = format;
                 ++m_textureParamsVersion;
             }

MobileGL/MG_Test/Texture/TextureTest.cpp

@@ -22,6 +22,7 @@
 #include <MG_State/EGLState/Core.h>
 #include <MG_State/GLState/Core.h>
 #include <MG_State/GLState/TextureState/TextureObject.h>
+#include <MG_State/GLState/TextureState/TextureObject2D.h>
 #include <MG_Util/Converters/GLToMG/TextureEnumConverter.h>
 #include <MG_Util/Converters/MGToGL/TextureEnumConverter.h>
 #include <MG_Util/Converters/MGToMG/TextureEnumConverter.h>
@@ -1840,6 +1841,46 @@ TEST_F(TextureTest, DefaultTextureIsBoundInitiallyAndIsPerTarget) {
               default2D);
 }
 
+// Backend sampled-set membership keys off IsUndefinedDefaultTexture, so a default texture
+// crossing the Unknown<->defined boundary must move the bind generation even though no bind
+// happened - a cached sampled set (DirectVulkan walk-skip) would otherwise replay stale
+// membership and never sync/transition the now-image-bearing default. Positioned while the 2D
+// default is still undefined in a single-process run (later tests define it and definedness is
+// irreversible through the GL API); the reverse transition at the end restores that state.
+TEST_F(TextureTest, DefiningImageOnBoundDefaultTextureBumpsBindGeneration) {
+    MG_Impl::GLImpl::ActiveTexture(GL_TEXTURE0);
+    MG_Impl::GLImpl::BindTexture(GL_TEXTURE_2D, 0);
+    const auto& defaultTexture =
+        MG_State::pGLContext->GetTextureUnitObject(0).GetBindingSlot(TextureTarget::Texture2D).GetBoundObject();
+    ASSERT_TRUE(MG_State::GLState::IsUndefinedDefaultTexture(defaultTexture.get()))
+        << "an earlier test defined the 2D default texture; move this test before it";
+
+    // glTexImage2D on the BOUND name-0 texture (no rebind anywhere) moves the generation
+    // exactly once: the next draw re-collects the sampled set and references the default's
+    // image instead of the fallback.
+    const Uint64 base = MG_State::pGLContext->GetTextureBindGeneration();
+    MG_Impl::GLImpl::TexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
+    EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);
+    EXPECT_EQ(MG_State::pGLContext->GetTextureBindGeneration(), base + 1);
+
+    // Re-specifying an already-defined default keeps the cache hot.
+    MG_Impl::GLImpl::TexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
+    EXPECT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);
+    EXPECT_EQ(MG_State::pGLContext->GetTextureBindGeneration(), base + 1);
+
+    // Other externalIndex-0 objects (proxy textures, default-FBO attachments) are not the
+    // context's default texture; their (re)specification must not churn the cache.
+    auto proxyLike = MakeShared<MG_State::GLState::TextureObject2D>(0u);
+    proxyLike->SetInternalFormat(TextureInternalFormat::RGBA8);
+    EXPECT_EQ(MG_State::pGLContext->GetTextureBindGeneration(), base + 1);
+
+    // The reverse transition (no GL entry point produces it today) is symmetric, and restores
+    // the undefined 2D default the rest of the suite expects.
+    defaultTexture->SetInternalFormat(TextureInternalFormat::Unknown);
+    EXPECT_EQ(MG_State::pGLContext->GetTextureBindGeneration(), base + 2);
+    EXPECT_TRUE(MG_State::GLState::IsUndefinedDefaultTexture(defaultTexture.get()));
+}
+
 TEST_F(TextureTest, DefaultTextureAcceptsImageAndParameterCalls) {
     MG_Impl::GLImpl::BindTexture(GL_TEXTURE_2D, 0);
     ASSERT_EQ(MG_Impl::GLImpl::GetError(), GL_NO_ERROR);