[Feat] (DirectVulkan, MG_Impl): occlusion queries via Vulkan query pools

GL_SAMPLES_PASSED / GL_ANY_SAMPLES_PASSED(_CONSERVATIVE) now work: every
app draw between Begin/EndQuery is wrapped in a slot of a host-reset
occlusion query pool (precise counts when occlusionQueryPrecise is
granted), and the result flush ends any active render pass before
submitting, waits, sums the slots and recycles them. ANY_* targets
report the boolean form; GL_QUERY_COUNTER_BITS and GL_CURRENT_QUERY
answer for the occlusion targets, and deleting an active query releases
its slot. Draw-time depth/stencil state also honors attachment absence:
a framebuffer without a depth (stencil) attachment behaves as if that
test always passes, even when a packed depth-stencil image is attached
through only one half (verify_partial_attachments.*).

MobileGL/MG_Backend/BackendObject.h

@@ -220,6 +220,11 @@ namespace MobileGL {
             // and leave the query readable later.
             Bool (*GetQueryResult64)(BackendQueryHandle query, Bool wait, Uint64* outNanoseconds);
             void (*DeleteBackendQuery)(BackendQueryHandle query);
+            // GL_SAMPLES_PASSED occlusion queries (optional; null = unsupported,
+            // the frontend then rejects the target). Results/deletion flow through
+            // GetQueryResult64 / DeleteBackendQuery like timer queries.
+            BackendQueryHandle (*BeginOcclusionQuery)();
+            void (*EndOcclusionQuery)(BackendQueryHandle query);
             Int64 (*GetGpuTimestampNs)(); // glGetInteger64v(GL_TIMESTAMP); 0 if unsupported
         };
         struct GlobalBackendFunctionsTable {

MobileGL/MG_Backend/DirectVulkan/BackendObject_DirectVulkan.cpp

@@ -635,6 +635,13 @@ namespace MobileGL::MG_Backend::DirectVulkan {
                 funcsTable.GL.DeleteBackendQuery = DeleteBackendQuery;
                 funcsTable.GL.GetGpuTimestampNs = GetGpuTimestampNs;
             }
+            // Occlusion queries share the handle-based result/delete entries, which must
+            // exist even when timer queries are disabled.
+            funcsTable.GL.BeginOcclusionQuery = BeginOcclusionQuery;
+            funcsTable.GL.EndOcclusionQuery = EndOcclusionQuery;
+            funcsTable.GL.IsQueryResultAvailable = IsQueryResultAvailable;
+            funcsTable.GL.GetQueryResult64 = GetQueryResult64;
+            funcsTable.GL.DeleteBackendQuery = DeleteBackendQuery;
             funcsTableInitialized = true;
         }
         return funcsTable;

MobileGL/MG_Backend/DirectVulkan/DirectVulkan.cpp

@@ -1564,8 +1564,12 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         // records are shared (SharedPtr) with the owning pool's pending list,
         // so deleting the query while results are still in flight is safe.
         struct VulkanTimerQuery {
+            enum class Kind : Uint8 { Timer, Occlusion };
+            Kind kind = Kind::Timer;
             SharedPtr<VkTimerQueryManager::TimestampRecord> begin;
             SharedPtr<VkTimerQueryManager::TimestampRecord> end;
+            // Kind::Occlusion - pool slots recorded between Begin/End; summed at result time.
+            Vector<Uint32> occlusionSlots;
             // Renderer generation the records were written under (see
             // g_rendererGeneration). A stale generation resolves as available
             // with a final zero result: the records' pool indices and frame
@@ -1655,6 +1659,15 @@ namespace MobileGL::MG_Backend::DirectVulkan {
             // ever be produced, so resolve with a final 0.
             return true;
         }
+        if (query->kind == VulkanTimerQuery::Kind::Occlusion) {
+            Uint64 samples = 0;
+            if (!pVulkanRenderer->ResolveOcclusionQueryResult(query->occlusionSlots, samples)) {
+                return false;
+            }
+            query->occlusionSlots.clear(); // slots are recycled by the resolve
+            *outNanoseconds = samples;
+            return true;
+        }
         // With wait, mirrors ClientWaitSync: a query ended this frame cannot
         // complete until Present submits the commands, so the wait refuses to
         // block on the current unsubmitted serial. Returning false keeps the
@@ -1687,6 +1700,26 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         delete static_cast<VulkanTimerQuery*>(handle);
     }
 
+    BackendQueryHandle BeginOcclusionQuery() {
+        MOBILEGL_ASSERT(pVulkanRenderer, "DirectVulkan::BeginOcclusionQuery called with null VulkanRenderer");
+        if (!pVulkanRenderer->StartOcclusionQueryCapture()) {
+            return nullptr;
+        }
+        auto* query = new VulkanTimerQuery{};
+        query->kind = VulkanTimerQuery::Kind::Occlusion;
+        query->rendererGeneration = GetRendererGeneration();
+        return query;
+    }
+
+    void EndOcclusionQuery(BackendQueryHandle handle) {
+        auto* query = static_cast<VulkanTimerQuery*>(handle);
+        MOBILEGL_ASSERT(pVulkanRenderer, "DirectVulkan::EndOcclusionQuery called with null VulkanRenderer");
+        if (query == nullptr || query->rendererGeneration != GetRendererGeneration()) {
+            return;
+        }
+        pVulkanRenderer->StopOcclusionQueryCapture(query->occlusionSlots);
+    }
+
     Int64 GetGpuTimestampNs() {
         // Vulkan cannot synchronously sample the GPU clock: timestamps only
         // exist as vkCmdWriteTimestamp results read back later, and

MobileGL/MG_Backend/DirectVulkan/DirectVulkan.h

@@ -123,6 +123,8 @@ namespace MobileGL::MG_Backend::DirectVulkan {
     // only while a live renderer exists whose device can actually time.
     Bool IsTimerQuerySupported();
     BackendQueryHandle BeginTimeElapsedQuery();
+    BackendQueryHandle BeginOcclusionQuery();
+    void EndOcclusionQuery(BackendQueryHandle query);
     void EndTimeElapsedQuery(BackendQueryHandle query);
     BackendQueryHandle QueryCounterTimestamp();
     Bool IsQueryResultAvailable(BackendQueryHandle query);

MobileGL/MG_Backend/DirectVulkan/Renderer/VulkanRenderer.cpp

@@ -2782,6 +2782,10 @@ void main() {
         }
         m_vertexInputStateFactory.reset();
         m_xfbCounterBuffer.Destroy();
+        if (m_occlusionQueryPool != VK_NULL_HANDLE) {
+            vkDestroyQueryPool(m_device, m_occlusionQueryPool, nullptr);
+            m_occlusionQueryPool = VK_NULL_HANDLE;
+        }
         m_bufferManager.Shutdown();
 
         // Device is idle (vkDeviceWaitIdle above); query pools can be destroyed.
@@ -4059,6 +4063,23 @@ void main() {
         auto colorLogicOpEnabled =
             MG_State::pGLContext->IsCapabilityEnabled(CapabilityInput::ColorLogicOp) && m_logicOpFeatureEnabled;
         auto stencilTestEnabled = MG_State::pGLContext->IsCapabilityEnabled(CapabilityInput::StencilTest);
+        // A framebuffer without a depth (stencil) attachment behaves as if the depth
+        // (stencil) test always passes and nothing is written - even when the bound
+        // image is a packed depth-stencil texture attached through only one half.
+        {
+            const auto& gatingFbo =
+                MG_State::pGLContext->GetFramebufferBindingSlot(FramebufferTarget::Draw).GetBoundObject();
+            if (gatingFbo != nullptr && !gatingFbo->IsDefaultFramebuffer()) {
+                const auto& depthAtt = gatingFbo->GetAttachment(MobileGL::FramebufferAttachmentType::Depth);
+                const auto& stencilAtt = gatingFbo->GetAttachment(MobileGL::FramebufferAttachmentType::Stencil);
+                if (!depthAtt.IsValid() || depthAtt.IsEmpty()) {
+                    depthTestEnabled = false;
+                }
+                if (!stencilAtt.IsValid() || stencilAtt.IsEmpty()) {
+                    stencilTestEnabled = false;
+                }
+            }
+        }
         const StencilFaceState& frontStencil = MG_State::pGLContext->GetStencilState(StencilFace::Front);
         const StencilFaceState& backStencil = MG_State::pGLContext->GetStencilState(StencilFace::Back);
         const VkPolygonMode requestedPolygonMode =
@@ -7767,14 +7788,95 @@ void main() {
         VkCommandBuffer& commandBuffer = frame.commandBuffer;
 
         const Bool xfbActive = BeginXfbCaptureForDraw(frame);
+        const Bool occlusionActive = BeginOcclusionForDraw(commandBuffer);
         vkCmdDraw(commandBuffer,
             payload.params.vertexCount,
             payload.params.instanceCount,
             payload.params.firstVertex,
             payload.params.firstInstance);
+        EndOcclusionForDraw(commandBuffer, occlusionActive);
         EndXfbCaptureForDraw(frame, xfbActive);
     }
 
+    Bool VulkanRenderer::StartOcclusionQueryCapture() {
+        if (!m_hostQueryResetEnabled || s_vkResetQueryPool == nullptr) {
+            return false;
+        }
+        if (m_occlusionQueryPool == VK_NULL_HANDLE) {
+            VkQueryPoolCreateInfo poolInfo{};
+            poolInfo.sType = VK_STRUCTURE_TYPE_QUERY_POOL_CREATE_INFO;
+            poolInfo.queryType = VK_QUERY_TYPE_OCCLUSION;
+            poolInfo.queryCount = kOcclusionQuerySlots;
+            if (vkCreateQueryPool(m_device, &poolInfo, nullptr, &m_occlusionQueryPool) != VK_SUCCESS) {
+                MGLOG_E("StartOcclusionQueryCapture: vkCreateQueryPool failed");
+                m_occlusionQueryPool = VK_NULL_HANDLE;
+                return false;
+            }
+            s_vkResetQueryPool(m_device, m_occlusionQueryPool, 0, kOcclusionQuerySlots);
+        }
+        m_occlusionActiveSlots.clear();
+        m_occlusionCaptureActive = true;
+        return true;
+    }
+
+    void VulkanRenderer::StopOcclusionQueryCapture(Vector<Uint32>& outSlots) {
+        outSlots = Move(m_occlusionActiveSlots);
+        m_occlusionActiveSlots.clear();
+        m_occlusionCaptureActive = false;
+    }
+
+    Bool VulkanRenderer::ResolveOcclusionQueryResult(const Vector<Uint32>& slots, Uint64& outSamples) {
+        outSamples = 0;
+        if (slots.empty()) {
+            return true;
+        }
+        if (m_occlusionQueryPool == VK_NULL_HANDLE) {
+            return true;
+        }
+        auto& frame = m_frameContext.GetCurrent();
+        if (frame.isCommandRecording) {
+            if (VkRenderPassManager::GetActiveRenderPass() != nullptr) {
+                VkRenderPassManager::EndRenderPass(frame.commandBuffer);
+            }
+            if (!SubmitReadbackCommandsAndWait(frame)) {
+                return false;
+            }
+        }
+        for (const Uint32 slot : slots) {
+            Uint64 value = 0;
+            const VkResult result =
+                vkGetQueryPoolResults(m_device, m_occlusionQueryPool, slot, 1, sizeof(value), &value, sizeof(value),
+                                      VK_QUERY_RESULT_64_BIT | VK_QUERY_RESULT_WAIT_BIT);
+            if (result == VK_SUCCESS) {
+                outSamples += value;
+            }
+            s_vkResetQueryPool(m_device, m_occlusionQueryPool, slot, 1);
+        }
+        return true;
+    }
+
+    Bool VulkanRenderer::BeginOcclusionForDraw(VkCommandBuffer commandBuffer) {
+        if (!m_occlusionCaptureActive || m_occlusionQueryPool == VK_NULL_HANDLE) {
+            return false;
+        }
+        const Uint32 slot = m_occlusionSlotCursor;
+        m_occlusionSlotCursor = (m_occlusionSlotCursor + 1) % kOcclusionQuerySlots;
+        // Slots recycle after their read; a wrapped-past unread slot is stale, so
+        // reset it here (host reset - the slot's prior GPU use has long retired).
+        s_vkResetQueryPool(m_device, m_occlusionQueryPool, slot, 1);
+        vkCmdBeginQuery(commandBuffer, m_occlusionQueryPool, slot,
+                        m_occlusionQueryPreciseEnabled ? VK_QUERY_CONTROL_PRECISE_BIT : 0);
+        m_occlusionActiveSlots.push_back(slot);
+        return true;
+    }
+
+    void VulkanRenderer::EndOcclusionForDraw(VkCommandBuffer commandBuffer, Bool began) {
+        if (!began) {
+            return;
+        }
+        vkCmdEndQuery(commandBuffer, m_occlusionQueryPool, m_occlusionActiveSlots.back());
+    }
+
     void VulkanRenderer::DrawElements(const DrawIndexedCmd& payload) {
         auto& frame = m_frameContext.GetCurrent();
 
@@ -7800,12 +7902,14 @@ void main() {
         VkCommandBuffer& commandBuffer = frame.commandBuffer;
 
         const Bool xfbActive = BeginXfbCaptureForDraw(frame);
+        const Bool occlusionActive = BeginOcclusionForDraw(commandBuffer);
         vkCmdDrawIndexed(commandBuffer,
             payload.params.indexCount,
             payload.params.instanceCount,
             payload.params.firstIndex,
             payload.params.vertexOffset,
             payload.params.firstInstance);
+        EndOcclusionForDraw(commandBuffer, occlusionActive);
         EndXfbCaptureForDraw(frame, xfbActive);
     }
 
@@ -9163,6 +9267,10 @@ void main() {
         // to isotropic filtering (and the extension goes unadvertised) when the device lacks it.
         deviceFeatures.samplerAnisotropy = supportedDeviceFeatures.samplerAnisotropy;
         m_samplerAnisotropyFeatureEnabled = deviceFeatures.samplerAnisotropy == VK_TRUE;
+        // GL_SAMPLES_PASSED needs exact sample counts; without the feature the boolean
+        // occlusion result still satisfies any-samples-style consumers.
+        deviceFeatures.occlusionQueryPrecise = supportedDeviceFeatures.occlusionQueryPrecise;
+        m_occlusionQueryPreciseEnabled = deviceFeatures.occlusionQueryPrecise == VK_TRUE;
 
         VkDeviceCreateInfo deviceCreateInfo{};
         deviceCreateInfo.sType = VK_STRUCTURE_TYPE_DEVICE_CREATE_INFO;
@@ -9309,6 +9417,27 @@ void main() {
             MGLOG_W("VK_EXT_transform_feedback is unavailable; transform feedback capture will not work");
         }
 
+        // Host query reset lets the occlusion-query ring recycle slots without a
+        // command-buffer round trip.
+        m_hostQueryResetEnabled = false;
+        VkPhysicalDeviceHostQueryResetFeatures hostQueryResetFeatures{};
+        hostQueryResetFeatures.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_HOST_QUERY_RESET_FEATURES;
+        if (IsExtensionSupported(availableExtensions, VK_EXT_HOST_QUERY_RESET_EXTENSION_NAME) &&
+            getPhysicalDeviceFeatures2 != nullptr) {
+            VkPhysicalDeviceFeatures2 featureQuery{};
+            featureQuery.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FEATURES_2;
+            featureQuery.pNext = &hostQueryResetFeatures;
+            getPhysicalDeviceFeatures2(m_physicalDevice.handle, &featureQuery);
+            if (hostQueryResetFeatures.hostQueryReset == VK_TRUE) {
+                if (!IsExtensionAlreadyEnabled(enabledDeviceExtensions, VK_EXT_HOST_QUERY_RESET_EXTENSION_NAME)) {
+                    enabledDeviceExtensions.push_back(VK_EXT_HOST_QUERY_RESET_EXTENSION_NAME);
+                }
+                hostQueryResetFeatures.pNext = const_cast<void*>(deviceCreateInfo.pNext);
+                deviceCreateInfo.pNext = &hostQueryResetFeatures;
+                m_hostQueryResetEnabled = true;
+            }
+        }
+
         deviceCreateInfo.enabledExtensionCount = static_cast<Uint32>(enabledDeviceExtensions.size());
         deviceCreateInfo.ppEnabledExtensionNames = enabledDeviceExtensions.data();
         MGLOG_I("Device feature support: robustBufferAccess=%s geometryShader=%s independentBlend=%s logicOp=%s shaderClipDistance=%s "
@@ -9378,6 +9507,17 @@ void main() {
                 m_transformFeedbackFeatureEnabled = false;
             }
         }
+        if (m_hostQueryResetEnabled) {
+            s_vkResetQueryPool =
+                reinterpret_cast<PFN_vkResetQueryPool>(vkGetDeviceProcAddr(m_device, "vkResetQueryPool"));
+            if (s_vkResetQueryPool == nullptr) {
+                s_vkResetQueryPool =
+                    reinterpret_cast<PFN_vkResetQueryPool>(vkGetDeviceProcAddr(m_device, "vkResetQueryPoolEXT"));
+            }
+            if (s_vkResetQueryPool == nullptr) {
+                m_hostQueryResetEnabled = false;
+            }
+        }
         MGLOG_I("index type uint8 enabled: %s", m_indexTypeUint8ExtensionEnabled ? "true" : "false");
         MGLOG_I("Logical device created.");
 

MobileGL/MG_Backend/DirectVulkan/Renderer/VulkanRenderer.h

@@ -296,6 +296,15 @@ namespace MobileGL::MG_Backend::DirectVulkan {
                                       const VkTimerQueryManager::TimestampRecord& end) const;
         Uint64 GetTimerQueryTimestampNs(const VkTimerQueryManager::TimestampRecord& record) const;
 
+        // GL_SAMPLES_PASSED occlusion queries: every app draw between Start and Stop is
+        // wrapped in a Vulkan occlusion query slot; the result is the slot sum. Requires
+        // hostQueryReset for slot recycling - Start fails (frontend keeps the query
+        // unsupported) when the device lacks it.
+        Bool StartOcclusionQueryCapture();
+        void StopOcclusionQueryCapture(Vector<Uint32>& outSlots);
+        // Flushes pending commands, waits, sums the slots, and recycles them.
+        Bool ResolveOcclusionQueryResult(const Vector<Uint32>& slots, Uint64& outSamples);
+
         void RequestSwapchainResize(Uint32 width, Uint32 height);
         // Re-query the surface and report whether the live swapchain no longer matches it
         // (size or orientation). This - not a VK_SUBOPTIMAL_KHR result - is what decides a
@@ -482,6 +491,18 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         // when GL transform feedback is active; binds capture buffers on demand.
         Bool BeginXfbCaptureForDraw(FrameContext::FrameData& frame);
         void EndXfbCaptureForDraw(FrameContext::FrameData& frame, Bool began);
+        // Wrap one app draw in an occlusion-query slot while a GL_SAMPLES_PASSED
+        // query is active. Returns whether a slot was begun (End must mirror it).
+        Bool BeginOcclusionForDraw(VkCommandBuffer commandBuffer);
+        void EndOcclusionForDraw(VkCommandBuffer commandBuffer, Bool began);
+        Bool m_occlusionQueryPreciseEnabled = false;
+        Bool m_hostQueryResetEnabled = false;
+        PFN_vkResetQueryPool s_vkResetQueryPool = nullptr;
+        VkQueryPool m_occlusionQueryPool = VK_NULL_HANDLE;
+        static constexpr Uint32 kOcclusionQuerySlots = 8192;
+        Uint32 m_occlusionSlotCursor = 0;
+        Bool m_occlusionCaptureActive = false;
+        Vector<Uint32> m_occlusionActiveSlots;
 
         VkCommandPool m_commandPool = VK_NULL_HANDLE;
 

MobileGL/MG_Impl/GLImpl/Query/GL_Query.cpp

@@ -46,6 +46,8 @@ namespace MobileGL::MG_Impl::GLImpl {
         // Ids of the queries active on the transform feedback targets (0 = none).
         GLuint g_activePrimitivesWrittenQueryId = 0;
         GLuint g_activePrimitivesGeneratedQueryId = 0;
+        // Id of the query active on GL_SAMPLES_PASSED (0 = none).
+        GLuint g_activeSamplesPassedQueryId = 0;
 
         Bool TimerQueryDisabled() {
             return MG_Config::Features.DisableTimerQuery;
@@ -131,6 +133,11 @@ namespace MobileGL::MG_Impl::GLImpl {
                         outValue = 0;
                         return true;
                     }
+                    // ANY_SAMPLES_PASSED* report a boolean.
+                    if (queryObject->target == GL_ANY_SAMPLES_PASSED ||
+                        queryObject->target == GL_ANY_SAMPLES_PASSED_CONSERVATIVE) {
+                        result = result != 0 ? 1 : 0;
+                    }
                     // Final value produced (or no GetQueryResult64 hook: the
                     // query degrades to a zero result); the backend handle is
                     // consumed and the value cached for later reads.
@@ -185,7 +192,24 @@ namespace MobileGL::MG_Impl::GLImpl {
             }
             QueryObject* queryObject = it->second;
             if (queryObject->active) {
-                EndTimeElapsedQueryLocked(queryObject); // implicitly end before deletion
+                // Implicitly end before deletion, releasing the matching active slot.
+                if (queryObject->target == GL_SAMPLES_PASSED || queryObject->target == GL_ANY_SAMPLES_PASSED ||
+                    queryObject->target == GL_ANY_SAMPLES_PASSED_CONSERVATIVE) {
+                    if (const auto endOcclusionQuery = MG_Backend::gBackendFunctionsTable.GL.EndOcclusionQuery;
+                        endOcclusionQuery && queryObject->backendHandle) {
+                        endOcclusionQuery(queryObject->backendHandle);
+                    }
+                    queryObject->active = false;
+                    g_activeSamplesPassedQueryId = 0;
+                } else if (queryObject->target == GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN ||
+                           queryObject->target == GL_PRIMITIVES_GENERATED) {
+                    queryObject->active = false;
+                    (queryObject->target == GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN
+                         ? g_activePrimitivesWrittenQueryId
+                         : g_activePrimitivesGeneratedQueryId) = 0;
+                } else {
+                    EndTimeElapsedQueryLocked(queryObject);
+                }
             }
             if (queryObject->backendHandle) {
                 if (const auto deleteBackendQuery = MG_Backend::gBackendFunctionsTable.GL.DeleteBackendQuery) {
@@ -211,10 +235,13 @@ namespace MobileGL::MG_Impl::GLImpl {
     void BeginQuery(GLenum target, GLuint id) {
         const Bool isTransformFeedbackQuery =
             target == GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN || target == GL_PRIMITIVES_GENERATED;
-        if (target != GL_TIME_ELAPSED && !isTransformFeedbackQuery) {
+        const Bool isOcclusionQuery =
-            // GL_TIME_ELAPSED timer queries and the transform feedback primitive
+            (target == GL_SAMPLES_PASSED || target == GL_ANY_SAMPLES_PASSED ||
-            // queries are implemented (occlusion queries remain stubs);
+             target == GL_ANY_SAMPLES_PASSED_CONSERVATIVE) &&
-            // GL_TIMESTAMP is not a valid BeginQuery target either.
+            MG_Backend::gBackendFunctionsTable.GL.BeginOcclusionQuery != nullptr;
+        if (target != GL_TIME_ELAPSED && !isTransformFeedbackQuery && !isOcclusionQuery) {
+            // GL_TIMESTAMP is not a valid BeginQuery target; the occlusion targets
+            // need backend support.
             RecordQueryError(ErrorCode::InvalidEnum, __FUNCTION__, "Query target is not supported.");
             return;
         }
@@ -231,7 +258,7 @@ namespace MobileGL::MG_Impl::GLImpl {
         GLuint& activeQueryId = isTransformFeedbackQuery
             ? (target == GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN ? g_activePrimitivesWrittenQueryId
                                                                   : g_activePrimitivesGeneratedQueryId)
-            : g_activeTimeElapsedQueryId;
+            : (isOcclusionQuery ? g_activeSamplesPassedQueryId : g_activeTimeElapsedQueryId);
         if (activeQueryId != 0) {
             RecordQueryError(ErrorCode::InvalidOperation, __FUNCTION__,
                              "A query is already active on this target.");
@@ -255,6 +282,8 @@ namespace MobileGL::MG_Impl::GLImpl {
             // result is the delta between Begin and End. Without geometry-stage
             // amplification the assembled count IS the written/generated count.
             queryObject->counterSnapshot = MG_State::pGLContext->GetTransformFeedbackPrimitiveCounter();
+        } else if (isOcclusionQuery) {
+            queryObject->backendHandle = MG_Backend::gBackendFunctionsTable.GL.BeginOcclusionQuery();
         } else {
             const auto beginTimeElapsedQuery = MG_Backend::gBackendFunctionsTable.GL.BeginTimeElapsedQuery;
             queryObject->backendHandle =
@@ -266,7 +295,11 @@ namespace MobileGL::MG_Impl::GLImpl {
     void EndQuery(GLenum target) {
         const Bool isTransformFeedbackQuery =
             target == GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN || target == GL_PRIMITIVES_GENERATED;
-        if (target != GL_TIME_ELAPSED && !isTransformFeedbackQuery) {
+        const Bool isOcclusionQuery =
+            (target == GL_SAMPLES_PASSED || target == GL_ANY_SAMPLES_PASSED ||
+             target == GL_ANY_SAMPLES_PASSED_CONSERVATIVE) &&
+            MG_Backend::gBackendFunctionsTable.GL.BeginOcclusionQuery != nullptr;
+        if (target != GL_TIME_ELAPSED && !isTransformFeedbackQuery && !isOcclusionQuery) {
             RecordQueryError(ErrorCode::InvalidEnum, __FUNCTION__, "Query target is not supported.");
             return;
         }
@@ -274,7 +307,7 @@ namespace MobileGL::MG_Impl::GLImpl {
         GLuint& activeQueryId = isTransformFeedbackQuery
             ? (target == GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN ? g_activePrimitivesWrittenQueryId
                                                                   : g_activePrimitivesGeneratedQueryId)
-            : g_activeTimeElapsedQueryId;
+            : (isOcclusionQuery ? g_activeSamplesPassedQueryId : g_activeTimeElapsedQueryId);
         if (activeQueryId == 0) {
             RecordQueryError(ErrorCode::InvalidOperation, __FUNCTION__, "No query is active on this target.");
             return;
@@ -293,6 +326,16 @@ namespace MobileGL::MG_Impl::GLImpl {
             activeQueryId = 0;
             return;
         }
+        if (isOcclusionQuery) {
+            if (const auto endOcclusionQuery = MG_Backend::gBackendFunctionsTable.GL.EndOcclusionQuery;
+                endOcclusionQuery && queryObject->backendHandle) {
+                endOcclusionQuery(queryObject->backendHandle);
+            }
+            queryObject->active = false;
+            queryObject->ended = true;
+            activeQueryId = 0;
+            return;
+        }
         EndTimeElapsedQueryLocked(queryObject);
     }
 
@@ -336,9 +379,25 @@ namespace MobileGL::MG_Impl::GLImpl {
         switch (pname) {
         case GL_CURRENT_QUERY: {
             const std::lock_guard<std::mutex> lock(g_queryObjectsMutex);
-            // Only GL_TIME_ELAPSED queries can be active; GL_TIMESTAMP queries
+            switch (target) {
-            // never are, and other targets remain unimplemented.
+            case GL_TIME_ELAPSED:
-            *params = target == GL_TIME_ELAPSED ? static_cast<GLint>(g_activeTimeElapsedQueryId) : 0;
+                *params = static_cast<GLint>(g_activeTimeElapsedQueryId);
+                break;
+            case GL_SAMPLES_PASSED:
+            case GL_ANY_SAMPLES_PASSED:
+            case GL_ANY_SAMPLES_PASSED_CONSERVATIVE:
+                *params = static_cast<GLint>(g_activeSamplesPassedQueryId);
+                break;
+            case GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN:
+                *params = static_cast<GLint>(g_activePrimitivesWrittenQueryId);
+                break;
+            case GL_PRIMITIVES_GENERATED:
+                *params = static_cast<GLint>(g_activePrimitivesGeneratedQueryId);
+                break;
+            default:
+                *params = 0;
+                break;
+            }
             return;
         }
         case GL_QUERY_COUNTER_BITS: {
@@ -346,7 +405,13 @@ namespace MobileGL::MG_Impl::GLImpl {
             // time: IsTimerQuerySupported is the dynamic truth (extension /
             // entry points / timestamp valid bits at call time, not at table
             // init), and the MOBILEGL_DISABLE_TIMERQUERY kill switch always
-            // wins. Non-timer targets remain unimplemented and report 0.
+            // wins.
+            if (target == GL_SAMPLES_PASSED || target == GL_ANY_SAMPLES_PASSED ||
+                target == GL_ANY_SAMPLES_PASSED_CONSERVATIVE) {
+                const Bool occlusionSupported = MG_Backend::gBackendFunctionsTable.GL.BeginOcclusionQuery != nullptr;
+                *params = occlusionSupported ? (target == GL_SAMPLES_PASSED ? 32 : 1) : 0;
+                return;
+            }
             const Bool timerTarget = target == GL_TIME_ELAPSED || target == GL_TIMESTAMP;
             const auto isTimerQuerySupported = MG_Backend::gBackendFunctionsTable.GL.IsTimerQuerySupported;
             const Bool supported =