[Feat] (MG_Backend/DirectVulkan): inital FBO implementation, and blit framebuffer

CMakeLists.txt

@@ -219,6 +219,7 @@ set(SOURCE_FILES
     MobileGL/MG_Backend/DirectVulkan/Renderer/VertexInputStateBuilder.cpp
     MobileGL/MG_Backend/DirectVulkan/Renderer/VertexInputStateFactory.cpp
     MobileGL/MG_Backend/DirectVulkan/Renderer/VkBufferObject.cpp
+    MobileGL/MG_Backend/DirectVulkan/Renderer/VkFramebufferManager.cpp
 
     MobileGL/MG_State/GLState/Core.cpp
     MobileGL/MG_State/GLState/ErrorState/Error.cpp

MobileGL/MG_Backend/DirectVulkan/DirectVulkan.cpp

@@ -8,6 +8,7 @@
 
 #include "DirectVulkan.h"
 #include "MG_State/GLState/Core.h"
+#include "MG_Impl/GLImpl/Framebuffer/GL_Framebuffer.h"
 
 namespace MobileGL::MG_Backend::DirectVulkan {
     UniquePtr<VulkanRenderer> pVulkanRenderer = nullptr;
@@ -16,10 +17,23 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         MOBILEGL_ASSERT(pVulkanRenderer, "DirectVulkan::Clear called with null VulkanRenderer");
         MOBILEGL_ASSERT(MG_State::pGLContext, "DirectVulkan::Clear called with null GL context");
 
+        const auto& drawFboSlot = MG_State::pGLContext->GetFramebufferBindingSlot(FramebufferTarget::Draw);
+        const auto drawFbo = drawFboSlot.GetBoundObject();
+        const auto defaultFboInfo = MG_Impl::GLImpl::FramebufferImpl::pDefaultFramebufferInfo;
+        const auto defaultFbo = defaultFboInfo ? defaultFboInfo->defaultFBO : nullptr;
+        const Bool isDefaultFboTarget = (drawFbo == defaultFbo) || (drawFbo == nullptr && defaultFbo != nullptr);
+        Uint drawFboExternalIndex = 0;
+        if (drawFbo) {
+            drawFboExternalIndex = drawFbo->GetExternalIndex();
+        } else if (defaultFbo) {
+            drawFboExternalIndex = defaultFbo->GetExternalIndex();
+        }
+
         const auto& clearColor = MG_State::pGLContext->GetClearColor();
         const auto clearDepth = MG_State::pGLContext->GetClearDepth();
         const auto clearStencil = static_cast<Uint32>(MG_State::pGLContext->GetClearStencil());
-        pVulkanRenderer->RequestClear(mask, clearColor, clearDepth, clearStencil);
+        pVulkanRenderer->RequestClear(mask, clearColor, clearDepth, clearStencil, drawFboExternalIndex,
+                                      isDefaultFboTarget);
     }
 
     void DrawElements(GLenum mode, GLsizei count, GLenum type, const void* indices) {
@@ -177,5 +191,34 @@ namespace MobileGL::MG_Backend::DirectVulkan {
 
         pVulkanRenderer->DrawArrays(payload);
     }
+
+    void BlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0, GLint dstX1,
+                         GLint dstY1, GLbitfield mask, GLenum filter) {
+        MOBILEGL_ASSERT(pVulkanRenderer, "DirectVulkan::BlitFramebuffer called with null VulkanRenderer");
+        MOBILEGL_ASSERT(MG_State::pGLContext, "DirectVulkan::BlitFramebuffer called with null GL context");
+
+        const auto readFbo = MG_State::pGLContext->GetFramebufferBindingSlot(FramebufferTarget::Read).GetBoundObject();
+        const auto drawFbo = MG_State::pGLContext->GetFramebufferBindingSlot(FramebufferTarget::Draw).GetBoundObject();
+        const auto defaultFboInfo = MG_Impl::GLImpl::FramebufferImpl::pDefaultFramebufferInfo;
+        const auto defaultFbo = defaultFboInfo ? defaultFboInfo->defaultFBO : nullptr;
+
+        const Bool readIsDefault = (readFbo == defaultFbo) || (readFbo == nullptr && defaultFbo != nullptr);
+        const Bool drawIsDefault = (drawFbo == defaultFbo) || (drawFbo == nullptr && defaultFbo != nullptr);
+        Uint readFboExternalIndex = 0;
+        Uint drawFboExternalIndex = 0;
+        if (readFbo) {
+            readFboExternalIndex = readFbo->GetExternalIndex();
+        } else if (defaultFbo) {
+            readFboExternalIndex = defaultFbo->GetExternalIndex();
+        }
+        if (drawFbo) {
+            drawFboExternalIndex = drawFbo->GetExternalIndex();
+        } else if (defaultFbo) {
+            drawFboExternalIndex = defaultFbo->GetExternalIndex();
+        }
+
+        pVulkanRenderer->BlitFramebuffer(srcX0, srcY0, srcX1, srcY1, dstX0, dstY0, dstX1, dstY1, mask, filter,
+                                         readFboExternalIndex, drawFboExternalIndex, readIsDefault, drawIsDefault);
+    }
 } // namespace MobileGL::MG_Backend::DirectVulkan
 

MobileGL/MG_Backend/DirectVulkan/Renderer/SwapchainObject.cpp

@@ -128,7 +128,20 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         createInfo.imageColorSpace = pickedSurfaceFormat.colorSpace;
         createInfo.imageExtent = swapchainCaps.currentExtent;
         createInfo.imageArrayLayers = 1;
-        createInfo.imageUsage = VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT;
+        const VkImageUsageFlags requiredImageUsage =
+            VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | VK_IMAGE_USAGE_TRANSFER_DST_BIT;
+        MOBILEGL_ASSERT((swapchainCaps.supportedUsageFlags & requiredImageUsage) == requiredImageUsage,
+                        "Swapchain does not support required usage flags (COLOR_ATTACHMENT | TRANSFER_DST). "
+                        "supportedUsageFlags=0x%x",
+                        static_cast<Uint32>(swapchainCaps.supportedUsageFlags));
+
+        VkImageUsageFlags imageUsage = requiredImageUsage;
+        if ((swapchainCaps.supportedUsageFlags & VK_IMAGE_USAGE_TRANSFER_SRC_BIT) != 0) {
+            imageUsage |= VK_IMAGE_USAGE_TRANSFER_SRC_BIT;
+        }
+        createInfo.imageUsage = imageUsage;
+        MGLOG_I("Swapchain imageUsage = 0x%x (supportedUsageFlags = 0x%x)", static_cast<Uint32>(createInfo.imageUsage),
+                static_cast<Uint32>(swapchainCaps.supportedUsageFlags));
         Uint32 queueFamilyIndices[] = {graphicsQueueFamily, presentQueueFamily};
         if (graphicsQueueFamily != presentQueueFamily) {
             createInfo.imageSharingMode = VK_SHARING_MODE_CONCURRENT;

MobileGL/MG_Backend/DirectVulkan/Renderer/VkFramebufferManager.cpp

@@ -0,0 +1,258 @@
+// MobileGL - MobileGL/MG_Backend/DirectVulkan/Renderer/VkFramebufferManager.cpp
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+#include "VkFramebufferManager.h"
+
+#include <MG_State/GLState/RenderbufferState/RenderbufferObject.h>
+#include <MG_State/GLState/TextureState/TextureEnum.h>
+
+namespace MobileGL::MG_Backend::DirectVulkan {
+    Bool VkFramebufferManager::Initialize(const InitInfo& initInfo) {
+        m_device = initInfo.device;
+        m_physicalDevice = initInfo.physicalDevice;
+        return m_device != VK_NULL_HANDLE && m_physicalDevice != VK_NULL_HANDLE;
+    }
+
+    void VkFramebufferManager::Shutdown() {
+        for (auto& [_, target] : m_offscreenColorTargets) {
+            DestroyOffscreenColorTarget(target);
+        }
+        m_offscreenColorTargets.clear();
+        m_device = VK_NULL_HANDLE;
+        m_physicalDevice = VK_NULL_HANDLE;
+    }
+
+    Bool VkFramebufferManager::EnsureOffscreenColorTarget(Uint glFboExternalIndex,
+                                                          const MG_State::GLState::FramebufferObject& glFbo) {
+        const auto& colorAttachment = glFbo.GetAttachment(FramebufferAttachmentType::Color0);
+        if (!colorAttachment.IsValid() || colorAttachment.IsEmpty()) {
+            MGLOG_W("VkFramebufferManager: FBO %u has no valid COLOR0 attachment", glFboExternalIndex);
+            return false;
+        }
+
+        const auto objectVersion = glFbo.GetObjectVersion();
+        auto& target = m_offscreenColorTargets[glFboExternalIndex];
+        if (target.image != VK_NULL_HANDLE && target.glObjectVersion == objectVersion) {
+            return true;
+        }
+
+        return RecreateOffscreenColorTarget(target, colorAttachment, objectVersion);
+    }
+
+    Bool VkFramebufferManager::ClearColor(VkCommandBuffer commandBuffer, Uint glFboExternalIndex,
+                                          const VkClearColorValue& clearColor) {
+        auto it = m_offscreenColorTargets.find(glFboExternalIndex);
+        if (it == m_offscreenColorTargets.end()) {
+            MGLOG_W("VkFramebufferManager::ClearColor skipped: no offscreen target for FBO %u", glFboExternalIndex);
+            return false;
+        }
+
+        auto& target = it->second;
+        if (!TransitionColorTargetForClear(commandBuffer, target)) {
+            return false;
+        }
+
+        VkImageSubresourceRange subresourceRange{};
+        subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+        subresourceRange.baseMipLevel = 0;
+        subresourceRange.levelCount = 1;
+        subresourceRange.baseArrayLayer = 0;
+        subresourceRange.layerCount = 1;
+        vkCmdClearColorImage(commandBuffer, target.image, target.layout, &clearColor, 1, &subresourceRange);
+        return true;
+    }
+
+    Bool VkFramebufferManager::TransitionOffscreenColorToTransferSrc(VkCommandBuffer commandBuffer,
+                                                                     Uint glFboExternalIndex) {
+        auto it = m_offscreenColorTargets.find(glFboExternalIndex);
+        if (it == m_offscreenColorTargets.end()) {
+            MGLOG_W("VkFramebufferManager::TransitionOffscreenColorToTransferSrc skipped: FBO %u not found",
+                    glFboExternalIndex);
+            return false;
+        }
+        return TransitionColorTargetForBlitSrc(commandBuffer, it->second);
+    }
+
+    Bool VkFramebufferManager::GetOffscreenColorImage(Uint glFboExternalIndex, VkImage& outImage,
+                                                      VkExtent2D& outExtent) const {
+        auto it = m_offscreenColorTargets.find(glFboExternalIndex);
+        if (it == m_offscreenColorTargets.end() || it->second.image == VK_NULL_HANDLE) {
+            return false;
+        }
+        outImage = it->second.image;
+        outExtent = it->second.extent;
+        return true;
+    }
+
+    Bool VkFramebufferManager::RecreateOffscreenColorTarget(
+        OffscreenColorTarget& target, const MG_State::GLState::FramebufferAttachmentObject& colorAttachment,
+        Uint16 glObjectVersion) {
+        DestroyOffscreenColorTarget(target);
+
+        const auto size = colorAttachment.GetSize();
+        if (size.x() <= 0 || size.y() <= 0) {
+            MGLOG_W("VkFramebufferManager: COLOR0 attachment size is invalid (%d, %d)", size.x(), size.y());
+            return false;
+        }
+
+        const VkFormat format = ResolveColorFormat(colorAttachment);
+        if (format == VK_FORMAT_UNDEFINED) {
+            MGLOG_W("VkFramebufferManager: COLOR0 attachment format is unsupported for Vulkan clear");
+            return false;
+        }
+
+        VkImageCreateInfo imageInfo{};
+        imageInfo.sType = VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO;
+        imageInfo.imageType = VK_IMAGE_TYPE_2D;
+        imageInfo.extent.width = static_cast<Uint32>(size.x());
+        imageInfo.extent.height = static_cast<Uint32>(size.y());
+        imageInfo.extent.depth = 1;
+        imageInfo.mipLevels = 1;
+        imageInfo.arrayLayers = 1;
+        imageInfo.format = format;
+        imageInfo.tiling = VK_IMAGE_TILING_OPTIMAL;
+        imageInfo.initialLayout = VK_IMAGE_LAYOUT_UNDEFINED;
+        imageInfo.usage = VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | VK_IMAGE_USAGE_TRANSFER_DST_BIT | VK_IMAGE_USAGE_TRANSFER_SRC_BIT;
+        imageInfo.samples = VK_SAMPLE_COUNT_1_BIT;
+        imageInfo.sharingMode = VK_SHARING_MODE_EXCLUSIVE;
+        VK_VERIFY(vkCreateImage(m_device, &imageInfo, nullptr, &target.image), "vkCreateImage(offscreen color)");
+
+        VkMemoryRequirements memoryRequirements{};
+        vkGetImageMemoryRequirements(m_device, target.image, &memoryRequirements);
+
+        VkMemoryAllocateInfo allocInfo{};
+        allocInfo.sType = VK_STRUCTURE_TYPE_MEMORY_ALLOCATE_INFO;
+        allocInfo.allocationSize = memoryRequirements.size;
+        allocInfo.memoryTypeIndex = FindMemoryType(memoryRequirements.memoryTypeBits, VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT);
+        VK_VERIFY(vkAllocateMemory(m_device, &allocInfo, nullptr, &target.memory), "vkAllocateMemory(offscreen color)");
+        VK_VERIFY(vkBindImageMemory(m_device, target.image, target.memory, 0), "vkBindImageMemory(offscreen color)");
+
+        VkImageViewCreateInfo viewInfo{};
+        viewInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
+        viewInfo.image = target.image;
+        viewInfo.viewType = VK_IMAGE_VIEW_TYPE_2D;
+        viewInfo.format = format;
+        viewInfo.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+        viewInfo.subresourceRange.baseMipLevel = 0;
+        viewInfo.subresourceRange.levelCount = 1;
+        viewInfo.subresourceRange.baseArrayLayer = 0;
+        viewInfo.subresourceRange.layerCount = 1;
+        VK_VERIFY(vkCreateImageView(m_device, &viewInfo, nullptr, &target.imageView), "vkCreateImageView(offscreen color)");
+
+        target.layout = VK_IMAGE_LAYOUT_UNDEFINED;
+        target.extent = {static_cast<Uint32>(size.x()), static_cast<Uint32>(size.y())};
+        target.format = format;
+        target.glObjectVersion = glObjectVersion;
+        return true;
+    }
+
+    void VkFramebufferManager::DestroyOffscreenColorTarget(OffscreenColorTarget& target) {
+        if (target.imageView != VK_NULL_HANDLE) {
+            vkDestroyImageView(m_device, target.imageView, nullptr);
+            target.imageView = VK_NULL_HANDLE;
+        }
+        if (target.image != VK_NULL_HANDLE) {
+            vkDestroyImage(m_device, target.image, nullptr);
+            target.image = VK_NULL_HANDLE;
+        }
+        if (target.memory != VK_NULL_HANDLE) {
+            vkFreeMemory(m_device, target.memory, nullptr);
+            target.memory = VK_NULL_HANDLE;
+        }
+        target.layout = VK_IMAGE_LAYOUT_UNDEFINED;
+        target.extent = {0, 0};
+        target.format = VK_FORMAT_UNDEFINED;
+        target.glObjectVersion = 0;
+    }
+
+    Bool VkFramebufferManager::TransitionColorTargetForClear(VkCommandBuffer commandBuffer, OffscreenColorTarget& target) {
+        if (target.layout == VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL) {
+            return true;
+        }
+
+        VkImageMemoryBarrier barrier{};
+        barrier.sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
+        barrier.srcAccessMask = 0;
+        barrier.dstAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
+        barrier.oldLayout = target.layout;
+        barrier.newLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL;
+        barrier.srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+        barrier.dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+        barrier.image = target.image;
+        barrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+        barrier.subresourceRange.baseMipLevel = 0;
+        barrier.subresourceRange.levelCount = 1;
+        barrier.subresourceRange.baseArrayLayer = 0;
+        barrier.subresourceRange.layerCount = 1;
+
+        vkCmdPipelineBarrier(commandBuffer, VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT, VK_PIPELINE_STAGE_TRANSFER_BIT,
+                             0, 0, nullptr, 0, nullptr, 1, &barrier);
+        target.layout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL;
+        return true;
+    }
+
+    Bool VkFramebufferManager::TransitionColorTargetForBlitSrc(VkCommandBuffer commandBuffer,
+                                                               OffscreenColorTarget& target) {
+        if (target.layout == VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL) {
+            return true;
+        }
+
+        VkImageMemoryBarrier barrier{};
+        barrier.sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
+        barrier.srcAccessMask = 0;
+        barrier.dstAccessMask = VK_ACCESS_TRANSFER_READ_BIT;
+        barrier.oldLayout = target.layout;
+        barrier.newLayout = VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL;
+        barrier.srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+        barrier.dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+        barrier.image = target.image;
+        barrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+        barrier.subresourceRange.baseMipLevel = 0;
+        barrier.subresourceRange.levelCount = 1;
+        barrier.subresourceRange.baseArrayLayer = 0;
+        barrier.subresourceRange.layerCount = 1;
+        vkCmdPipelineBarrier(commandBuffer, VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT, VK_PIPELINE_STAGE_TRANSFER_BIT,
+                             0, 0, nullptr, 0, nullptr, 1, &barrier);
+        target.layout = VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL;
+        return true;
+    }
+
+    Uint32 VkFramebufferManager::FindMemoryType(Uint32 typeFilter, VkMemoryPropertyFlags properties) const {
+        VkPhysicalDeviceMemoryProperties memoryProperties{};
+        vkGetPhysicalDeviceMemoryProperties(m_physicalDevice, &memoryProperties);
+        for (Uint32 i = 0; i < memoryProperties.memoryTypeCount; ++i) {
+            if ((typeFilter & (1U << i)) &&
+                (memoryProperties.memoryTypes[i].propertyFlags & properties) == properties) {
+                return i;
+            }
+        }
+        MOBILEGL_ASSERT(false, "VkFramebufferManager::FindMemoryType failed");
+        return 0;
+    }
+
+    VkFormat VkFramebufferManager::ResolveColorFormat(
+        const MG_State::GLState::FramebufferAttachmentObject& colorAttachment) {
+        TextureInternalFormat internalFormat = TextureInternalFormat::Unknown;
+        if (colorAttachment.IsTexture()) {
+            const auto texture = colorAttachment.GetTexture();
+            internalFormat = texture ? texture->GetFormat() : TextureInternalFormat::Unknown;
+        } else if (colorAttachment.IsRenderbuffer()) {
+            const auto renderbuffer = colorAttachment.GetRenderbuffer();
+            internalFormat = renderbuffer ? renderbuffer->GetInternalFormat() : TextureInternalFormat::Unknown;
+        }
+
+        switch (internalFormat) {
+        case TextureInternalFormat::RGBA:
+        case TextureInternalFormat::RGBA8:
+        case TextureInternalFormat::SRGB8Alpha8:
+            return VK_FORMAT_R8G8B8A8_UNORM;
+        default:
+            return VK_FORMAT_UNDEFINED;
+        }
+    }
+} // namespace MobileGL::MG_Backend::DirectVulkan

MobileGL/MG_Backend/DirectVulkan/Renderer/VkFramebufferManager.h

@@ -0,0 +1,58 @@
+// MobileGL - MobileGL/MG_Backend/DirectVulkan/Renderer/VkFramebufferManager.h
+// Copyright (c) 2025-2026 MobileGL-Dev
+// Licensed under the GNU Lesser General Public License v3.0:
+//   https://www.gnu.org/licenses/gpl-3.0.txt
+//   https://www.gnu.org/licenses/lgpl-3.0.txt
+// SPDX-License-Identifier: LGPL-3.0-only
+// End of Source File Header
+
+#pragma once
+
+#include "../VkIncludes.h"
+#include <Includes.h>
+#include <MG_State/GLState/FramebufferState/FramebufferObject.h>
+
+namespace MobileGL::MG_Backend::DirectVulkan {
+    class VkFramebufferManager {
+    public:
+        struct InitInfo {
+            VkDevice device = VK_NULL_HANDLE;
+            VkPhysicalDevice physicalDevice = VK_NULL_HANDLE;
+        };
+
+        VkFramebufferManager() = default;
+        ~VkFramebufferManager() = default;
+
+        Bool Initialize(const InitInfo& initInfo);
+        void Shutdown();
+
+        Bool EnsureOffscreenColorTarget(Uint glFboExternalIndex, const MG_State::GLState::FramebufferObject& glFbo);
+        Bool ClearColor(VkCommandBuffer commandBuffer, Uint glFboExternalIndex, const VkClearColorValue& clearColor);
+        Bool TransitionOffscreenColorToTransferSrc(VkCommandBuffer commandBuffer, Uint glFboExternalIndex);
+        Bool GetOffscreenColorImage(Uint glFboExternalIndex, VkImage& outImage, VkExtent2D& outExtent) const;
+
+    private:
+        struct OffscreenColorTarget {
+            VkImage image = VK_NULL_HANDLE;
+            VkDeviceMemory memory = VK_NULL_HANDLE;
+            VkImageView imageView = VK_NULL_HANDLE;
+            VkImageLayout layout = VK_IMAGE_LAYOUT_UNDEFINED;
+            VkExtent2D extent = {0, 0};
+            VkFormat format = VK_FORMAT_UNDEFINED;
+            Uint16 glObjectVersion = 0;
+        };
+
+        Bool RecreateOffscreenColorTarget(OffscreenColorTarget& target,
+                                          const MG_State::GLState::FramebufferAttachmentObject& colorAttachment,
+                                          Uint16 glObjectVersion);
+        void DestroyOffscreenColorTarget(OffscreenColorTarget& target);
+        Bool TransitionColorTargetForClear(VkCommandBuffer commandBuffer, OffscreenColorTarget& target);
+        Bool TransitionColorTargetForBlitSrc(VkCommandBuffer commandBuffer, OffscreenColorTarget& target);
+        Uint32 FindMemoryType(Uint32 typeFilter, VkMemoryPropertyFlags properties) const;
+        static VkFormat ResolveColorFormat(const MG_State::GLState::FramebufferAttachmentObject& colorAttachment);
+
+        VkDevice m_device = VK_NULL_HANDLE;
+        VkPhysicalDevice m_physicalDevice = VK_NULL_HANDLE;
+        UnorderedMap<Uint, OffscreenColorTarget> m_offscreenColorTargets;
+    };
+} // namespace MobileGL::MG_Backend::DirectVulkan

MobileGL/MG_Backend/DirectVulkan/Renderer/VulkanRenderer.cpp

@@ -10,6 +10,7 @@
 #include "VertexInputStateFactory.h"
 #include "VertexInputStateBuilder.h"
 
+#include "MG_State/GLState/Core.h"
 #include "MG_State/GLState/ProgramState/ProgramObject.h"
 
 namespace MobileGL::MG_Backend::DirectVulkan {
@@ -130,6 +131,11 @@ namespace MobileGL::MG_Backend::DirectVulkan {
             m_uniformDescriptorBinder.reset();
         }
         m_vertexInputStateFactory = MakeUnique<VertexInputStateFactory>(m_config);
+        m_framebufferManager = MakeUnique<VkFramebufferManager>();
+        if (!m_framebufferManager->Initialize({m_device, m_physicalDevice.handle})) {
+            MGLOG_E("VkFramebufferManager initialization failed. Offscreen FBO clear path is disabled.");
+            m_framebufferManager.reset();
+        }
 
         PrepareDemoPipeline();
         CreateFrameContexts();
@@ -147,6 +153,10 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         m_pipelineFactory.reset();
         m_programFactory.reset();
         m_vertexInputStateFactory.reset();
+        if (m_framebufferManager) {
+            m_framebufferManager->Shutdown();
+            m_framebufferManager.reset();
+        }
         for (auto& vertexBuffer : m_vertexBuffers) {
             if (vertexBuffer) {
                 vertexBuffer->Destroy();
@@ -197,13 +207,22 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         MGLOG_I("VulkanRenderer shut down completed");
     }
 
-    void VulkanRenderer::RequestClear(GLbitfield mask, const FloatVec4& color, Float depth, Uint32 stencil) {
+    void VulkanRenderer::RequestClear(GLbitfield mask, const FloatVec4& color, Float depth, Uint32 stencil,
+                                      Uint drawFboExternalIndex, Bool isDefaultFramebufferTarget) {
         const GLbitfield supportedMask = GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT;
         const GLbitfield requestMask = (mask & supportedMask);
         if (requestMask == 0) {
             return;
         }
 
+        if (m_pendingClearMask != 0 &&
+            (m_pendingClearDrawFboExternalIndex != drawFboExternalIndex ||
+             m_pendingClearTargetsDefaultFramebuffer != isDefaultFramebufferTarget)) {
+            MGLOG_W("Pending clear target changed from FBO %u to FBO %u before execution; dropping previous pending clear",
+                    m_pendingClearDrawFboExternalIndex, drawFboExternalIndex);
+            m_pendingClearMask = 0;
+        }
+
         if ((requestMask & GL_COLOR_BUFFER_BIT) != 0) {
             m_pendingClearColor.float32[0] = color.x();
             m_pendingClearColor.float32[1] = color.y();
@@ -216,6 +235,8 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         if ((requestMask & GL_STENCIL_BUFFER_BIT) != 0) {
             m_pendingClearStencil = stencil;
         }
+        m_pendingClearDrawFboExternalIndex = drawFboExternalIndex;
+        m_pendingClearTargetsDefaultFramebuffer = isDefaultFramebufferTarget;
         m_pendingClearMask |= requestMask;
     }
 
@@ -330,6 +351,22 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         m_depthStencilImageLayouts[imageIndex] = VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL;
     }
 
+    Bool VulkanRenderer::RecordOffscreenColorClear(VkCommandBuffer commandBuffer) {
+        if (!m_framebufferManager || !MG_State::pGLContext) {
+            return false;
+        }
+
+        const auto fbo = MG_State::pGLContext->GetFramebufferObject(m_pendingClearDrawFboExternalIndex);
+        if (!fbo) {
+            MGLOG_W("RecordOffscreenColorClear skipped: draw FBO %u not found", m_pendingClearDrawFboExternalIndex);
+            return false;
+        }
+        if (!m_framebufferManager->EnsureOffscreenColorTarget(m_pendingClearDrawFboExternalIndex, *fbo)) {
+            return false;
+        }
+        return m_framebufferManager->ClearColor(commandBuffer, m_pendingClearDrawFboExternalIndex, m_pendingClearColor);
+    }
+
     void VulkanRenderer::EnsureFrameRecordingStarted() {
         auto& frame = m_frameContext.GetCurrent();
         if (frame.isCommandRecording) {
@@ -345,6 +382,47 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         if (m_uniformDescriptorBinder) {
             m_uniformDescriptorBinder->BeginFrame(m_frameContext.GetCurrentFrameIndex());
         }
+
+        if (m_pendingClearMask != 0 && !m_pendingClearTargetsDefaultFramebuffer) {
+            if ((m_pendingClearMask & GL_COLOR_BUFFER_BIT) != 0) {
+                if (!RecordOffscreenColorClear(commandBuffer)) {
+                    MGLOG_W("Failed to clear non-default FBO %u color attachment",
+                            m_pendingClearDrawFboExternalIndex);
+                }
+                m_pendingClearMask &= ~GL_COLOR_BUFFER_BIT;
+            }
+            if ((m_pendingClearMask & (GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT)) != 0) {
+                MGLOG_W("Depth/stencil clear on non-default FBO is not implemented yet (FBO %u)",
+                        m_pendingClearDrawFboExternalIndex);
+                m_pendingClearMask &= ~(GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+            }
+
+            // This frame touched only offscreen resources. Present still requires
+            // the acquired swapchain image to be in PRESENT layout.
+            const auto swapchainOldLayout = m_swapchainObject.GetImageLayout(m_imageIndexAcquired);
+            if (swapchainOldLayout != VK_IMAGE_LAYOUT_PRESENT_SRC_KHR &&
+                swapchainOldLayout != VK_IMAGE_LAYOUT_SHARED_PRESENT_KHR) {
+                VkImageMemoryBarrier presentBarrier{};
+                presentBarrier.sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
+                presentBarrier.srcAccessMask = 0;
+                presentBarrier.dstAccessMask = 0;
+                presentBarrier.oldLayout = swapchainOldLayout;
+                presentBarrier.newLayout = VK_IMAGE_LAYOUT_PRESENT_SRC_KHR;
+                presentBarrier.srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+                presentBarrier.dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+                presentBarrier.image = m_swapchainObject.GetImage(m_imageIndexAcquired);
+                presentBarrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+                presentBarrier.subresourceRange.baseMipLevel = 0;
+                presentBarrier.subresourceRange.levelCount = 1;
+                presentBarrier.subresourceRange.baseArrayLayer = 0;
+                presentBarrier.subresourceRange.layerCount = 1;
+                vkCmdPipelineBarrier(commandBuffer, VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT, VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
+                                     0, 0, nullptr, 0, nullptr, 1, &presentBarrier);
+                m_swapchainObject.SetImageLayout(m_imageIndexAcquired, VK_IMAGE_LAYOUT_PRESENT_SRC_KHR);
+            }
+            return;
+        }
+
         TransitionSwapchainImageToColorAttachment(commandBuffer, m_imageIndexAcquired);
         TransitionDepthStencilImageToAttachment(commandBuffer, m_imageIndexAcquired);
 
@@ -648,6 +726,124 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         vkCmdDrawIndexed(commandBuffer, static_cast<Uint32>(payload.drawArray.count), 1, 0, 0, 0);
     }
 
+    Bool VulkanRenderer::BlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0,
+                                         GLint dstX1, GLint dstY1, GLbitfield mask, GLenum filter,
+                                         Uint readFboExternalIndex, Uint drawFboExternalIndex,
+                                         Bool readIsDefaultFramebuffer, Bool drawIsDefaultFramebuffer) {
+        if ((mask & GL_COLOR_BUFFER_BIT) == 0 || (mask & ~GL_COLOR_BUFFER_BIT) != 0) {
+            MGLOG_W("BlitFramebuffer skipped: only GL_COLOR_BUFFER_BIT is supported in Vulkan backend for now");
+            return false;
+        }
+        if (readIsDefaultFramebuffer || !drawIsDefaultFramebuffer) {
+            MGLOG_W("BlitFramebuffer skipped: currently only read=offscreen FBO and draw=default FBO is supported");
+            return false;
+        }
+
+        auto& frame = m_frameContext.GetCurrent();
+        if (frame.hasCommandBufferRecorded) {
+            MGLOG_W("BlitFramebuffer skipped: current frame command buffer is already finalized");
+            return false;
+        }
+
+        if (!frame.isCommandRecording) {
+            m_frameContext.BeginCommandRecording();
+            if (m_uniformDescriptorBinder) {
+                m_uniformDescriptorBinder->BeginFrame(m_frameContext.GetCurrentFrameIndex());
+            }
+        }
+
+        VkCommandBuffer commandBuffer = frame.commandBuffer;
+        if (m_isMainRenderPassActive) {
+            vkCmdEndRenderPass(commandBuffer);
+            m_isMainRenderPassActive = false;
+        }
+
+        if (!m_framebufferManager || !MG_State::pGLContext) {
+            MGLOG_W("BlitFramebuffer skipped: framebuffer manager is unavailable");
+            return false;
+        }
+
+        (void)drawFboExternalIndex;
+        const auto readFbo = MG_State::pGLContext->GetFramebufferObject(readFboExternalIndex);
+        if (!readFbo) {
+            MGLOG_W("BlitFramebuffer skipped: read FBO %u not found", readFboExternalIndex);
+            return false;
+        }
+        if (!m_framebufferManager->EnsureOffscreenColorTarget(readFboExternalIndex, *readFbo)) {
+            return false;
+        }
+        if (!m_framebufferManager->TransitionOffscreenColorToTransferSrc(commandBuffer, readFboExternalIndex)) {
+            return false;
+        }
+
+        VkImage srcImage = VK_NULL_HANDLE;
+        VkExtent2D srcExtent{};
+        if (!m_framebufferManager->GetOffscreenColorImage(readFboExternalIndex, srcImage, srcExtent)) {
+            MGLOG_W("BlitFramebuffer skipped: offscreen image for FBO %u is unavailable", readFboExternalIndex);
+            return false;
+        }
+
+        const auto swapchainOldLayout = m_swapchainObject.GetImageLayout(m_imageIndexAcquired);
+        if (swapchainOldLayout != VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL) {
+            VkImageMemoryBarrier toTransferDstBarrier{};
+            toTransferDstBarrier.sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
+            toTransferDstBarrier.srcAccessMask = 0;
+            toTransferDstBarrier.dstAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
+            toTransferDstBarrier.oldLayout = swapchainOldLayout;
+            toTransferDstBarrier.newLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL;
+            toTransferDstBarrier.srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+            toTransferDstBarrier.dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+            toTransferDstBarrier.image = m_swapchainObject.GetImage(m_imageIndexAcquired);
+            toTransferDstBarrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+            toTransferDstBarrier.subresourceRange.baseMipLevel = 0;
+            toTransferDstBarrier.subresourceRange.levelCount = 1;
+            toTransferDstBarrier.subresourceRange.baseArrayLayer = 0;
+            toTransferDstBarrier.subresourceRange.layerCount = 1;
+            vkCmdPipelineBarrier(commandBuffer, VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT, VK_PIPELINE_STAGE_TRANSFER_BIT,
+                                 0, 0, nullptr, 0, nullptr, 1, &toTransferDstBarrier);
+            m_swapchainObject.SetImageLayout(m_imageIndexAcquired, VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL);
+        }
+
+        VkImageBlit blitRegion{};
+        blitRegion.srcSubresource.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+        blitRegion.srcSubresource.mipLevel = 0;
+        blitRegion.srcSubresource.baseArrayLayer = 0;
+        blitRegion.srcSubresource.layerCount = 1;
+        blitRegion.srcOffsets[0] = {srcX0, srcY0, 0};
+        blitRegion.srcOffsets[1] = {srcX1, srcY1, 1};
+        blitRegion.dstSubresource.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+        blitRegion.dstSubresource.mipLevel = 0;
+        blitRegion.dstSubresource.baseArrayLayer = 0;
+        blitRegion.dstSubresource.layerCount = 1;
+        blitRegion.dstOffsets[0] = {dstX0, dstY0, 0};
+        blitRegion.dstOffsets[1] = {dstX1, dstY1, 1};
+
+        vkCmdBlitImage(commandBuffer, srcImage, VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL,
+                       m_swapchainObject.GetImage(m_imageIndexAcquired), VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
+                       1, &blitRegion, (filter == GL_LINEAR ? VK_FILTER_LINEAR : VK_FILTER_NEAREST));
+
+        VkImageMemoryBarrier toPresentBarrier{};
+        toPresentBarrier.sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
+        toPresentBarrier.srcAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
+        toPresentBarrier.dstAccessMask = 0;
+        toPresentBarrier.oldLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL;
+        toPresentBarrier.newLayout = VK_IMAGE_LAYOUT_PRESENT_SRC_KHR;
+        toPresentBarrier.srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+        toPresentBarrier.dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
+        toPresentBarrier.image = m_swapchainObject.GetImage(m_imageIndexAcquired);
+        toPresentBarrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+        toPresentBarrier.subresourceRange.baseMipLevel = 0;
+        toPresentBarrier.subresourceRange.levelCount = 1;
+        toPresentBarrier.subresourceRange.baseArrayLayer = 0;
+        toPresentBarrier.subresourceRange.layerCount = 1;
+        vkCmdPipelineBarrier(commandBuffer, VK_PIPELINE_STAGE_TRANSFER_BIT, VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
+                             0, 0, nullptr, 0, nullptr, 1, &toPresentBarrier);
+        m_swapchainObject.SetImageLayout(m_imageIndexAcquired, VK_IMAGE_LAYOUT_PRESENT_SRC_KHR);
+
+        (void)srcExtent;
+        return true;
+    }
+
     void VulkanRenderer::Render() {
         // Route test rendering through the same frame-start logic used by draw calls,
         // so pending glClear() state can be consumed consistently.
@@ -669,7 +865,11 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         MOBILEGL_ASSERT(m_imageIndexAcquired < m_swapchainObject.GetImageCount(),
                         "Present, acquired image index out of range");
         auto& frame = m_frameContext.GetCurrent();
-        if (m_pendingClearMask != 0 && frame.isCommandRecording && m_isMainRenderPassActive) {
+        if (m_pendingClearMask != 0 && frame.hasCommandBufferRecorded) {
+            MGLOG_W("Dropping pending clear for current frame because command buffer is already finalized");
+            m_pendingClearMask = 0;
+        } else if (m_pendingClearMask != 0 && frame.isCommandRecording) {
+            if (m_pendingClearTargetsDefaultFramebuffer && m_isMainRenderPassActive) {
                 if ((m_pendingClearMask & GL_COLOR_BUFFER_BIT) != 0) {
                     RecordColorClear(frame.commandBuffer, m_pendingClearColor);
                 }
@@ -677,9 +877,23 @@ namespace MobileGL::MG_Backend::DirectVulkan {
                     RecordDepthStencilClear(frame.commandBuffer, m_pendingClearMask, m_pendingClearDepth, m_pendingClearStencil);
                 }
                 m_pendingClearMask = 0;
-        } else if (m_pendingClearMask != 0 && frame.hasCommandBufferRecorded) {
+            } else if (!m_pendingClearTargetsDefaultFramebuffer) {
-            MGLOG_W("Dropping pending clear for current frame because command buffer is already finalized");
+                if ((m_pendingClearMask & GL_COLOR_BUFFER_BIT) != 0) {
+                    if (!RecordOffscreenColorClear(frame.commandBuffer)) {
+                        MGLOG_W("Present: failed to clear non-default FBO %u color attachment",
+                                m_pendingClearDrawFboExternalIndex);
+                    }
+                    m_pendingClearMask &= ~GL_COLOR_BUFFER_BIT;
+                }
+                if ((m_pendingClearMask & (GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT)) != 0) {
+                    MGLOG_W("Present: depth/stencil clear on non-default FBO is not implemented yet (FBO %u)",
+                            m_pendingClearDrawFboExternalIndex);
+                    m_pendingClearMask &= ~(GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+                }
+            } else {
+                MGLOG_W("Present: pending default-FBO clear cannot execute because no render pass is active");
                 m_pendingClearMask = 0;
+            }
         } else if (m_pendingClearMask != 0) {
             EnsureFrameRecordingStarted();
         }

MobileGL/MG_Backend/DirectVulkan/Renderer/VulkanRenderer.h

@@ -15,6 +15,7 @@
 #include "UniformDescriptorBinder.h"
 #include "VertexInputStateFactory.h"
 #include "VkBufferObject.h"
+#include "VkFramebufferManager.h"
 #include "MG_Util/Math/VectorTypes.h"
 #include <Includes.h>
 #include <vk_mem_alloc.h>
@@ -58,11 +59,15 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         void Initialize();
         void Shutdown();
 
-        void RequestClear(GLbitfield mask, const FloatVec4& color, Float depth, Uint32 stencil);
+        void RequestClear(GLbitfield mask, const FloatVec4& color, Float depth, Uint32 stencil,
+                          Uint drawFboExternalIndex, Bool isDefaultFramebufferTarget);
         Bool ConsumePendingColorClear(VkClearColorValue& outClearColor);
         void EnsureFrameRecordingStarted();
         void DrawArrays(const DrawArrayPayload& payload);
         void DrawElements(const DrawElementPayload& payload);
+        Bool BlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0, GLint dstX1,
+                             GLint dstY1, GLbitfield mask, GLenum filter, Uint readFboExternalIndex,
+                             Uint drawFboExternalIndex, Bool readIsDefaultFramebuffer, Bool drawIsDefaultFramebuffer);
         void Render();
         void Present();
 
@@ -128,12 +133,15 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         VkClearColorValue m_pendingClearColor = {{0.0f, 0.0f, 0.0f, 1.0f}};
         Float m_pendingClearDepth = 1.0f;
         Uint32 m_pendingClearStencil = 0;
+        Uint m_pendingClearDrawFboExternalIndex = 0;
+        Bool m_pendingClearTargetsDefaultFramebuffer = true;
         Bool m_isMainRenderPassActive = false;
 
         UniquePtr<PipelineFactory> m_pipelineFactory;
         UniquePtr<ProgramFactory> m_programFactory;
         UniquePtr<UniformDescriptorBinder> m_uniformDescriptorBinder;
         UniquePtr<VertexInputStateFactory> m_vertexInputStateFactory;
+        UniquePtr<VkFramebufferManager> m_framebufferManager;
 
         void CreateInstance();
         VkResult SetupDebugMessenger();
@@ -159,6 +167,7 @@ namespace MobileGL::MG_Backend::DirectVulkan {
         void TransitionDepthStencilImageToAttachment(VkCommandBuffer commandBuffer, Uint32 imageIndex);
         void RecordColorClear(VkCommandBuffer commandBuffer, const VkClearColorValue& clearColor);
         void RecordDepthStencilClear(VkCommandBuffer commandBuffer, GLbitfield mask, Float depth, Uint32 stencil);
+        Bool RecordOffscreenColorClear(VkCommandBuffer commandBuffer);
         void EndFrameRecordingIfNeeded();
         Bool UploadAndBindVertexStreams(
             const VertexInputStateFactory::BackendVertexInputState& vertexInputState,

MobileGL/MG_Impl/GLImpl/Framebuffer/GL_Framebuffer.cpp

@@ -19,6 +19,9 @@
 #if MOBILEGL_BACKEND == MOBILEGL_BACKEND_TYPE_DIRECT_GLES
 #include <MG_Backend/DirectGLES/DirectGLES.h>
 #endif
+#if MOBILEGL_BACKEND == MOBILEGL_BACKEND_TYPE_DIRECT_VULKAN
+#include <MG_Backend/DirectVulkan/DirectVulkan.h>
+#endif
 
 namespace MobileGL {
     namespace MG_Impl::GLImpl {
@@ -27,9 +30,69 @@ namespace MobileGL {
 #if MOBILEGL_BACKEND == MOBILEGL_BACKEND_TYPE_DIRECT_GLES
             MG_Backend::DirectGLES::BlitFramebuffer(srcX0, srcY0, srcX1, srcY1, dstX0, dstY0, dstX1, dstY1, mask,
                                                     filter);
+#elif MOBILEGL_BACKEND == MOBILEGL_BACKEND_TYPE_DIRECT_VULKAN
+            MG_Backend::DirectVulkan::BlitFramebuffer(srcX0, srcY0, srcX1, srcY1, dstX0, dstY0, dstX1, dstY1, mask,
+                                                      filter);
 #endif
         }
 
+        Bool BlitFramebuffer_State(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0,
+                                   GLint dstX1, GLint dstY1, GLbitfield mask, GLenum filter) {
+            (void)srcX0;
+            (void)srcY0;
+            (void)srcX1;
+            (void)srcY1;
+            (void)dstX0;
+            (void)dstY0;
+            (void)dstX1;
+            (void)dstY1;
+
+            constexpr GLbitfield kSupportedMask = GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT;
+            if ((mask & kSupportedMask) == 0 || (mask & ~kSupportedMask) != 0) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidValue,
+                    MakeShared<GenericErrorInfo>("MG_Impl/GLImpl", __func__,
+                                                 "`mask` must contain COLOR/DEPTH/STENCIL bits only."));
+                return false;
+            }
+
+            if (filter != GL_NEAREST && filter != GL_LINEAR) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidEnum,
+                    MakeShared<GenericErrorInfo>("MG_Impl/GLImpl", __func__,
+                                                 "`filter` must be GL_NEAREST or GL_LINEAR."));
+                return false;
+            }
+
+            if ((mask & (GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT)) != 0 && filter != GL_NEAREST) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidOperation,
+                    MakeShared<GenericErrorInfo>("MG_Impl/GLImpl", __func__,
+                                                 "Depth/stencil blit requires GL_NEAREST filter."));
+                return false;
+            }
+
+            const auto readFbo = MG_State::pGLContext->GetFramebufferBindingSlot(FramebufferTarget::Read).GetBoundObject();
+            const auto drawFbo = MG_State::pGLContext->GetFramebufferBindingSlot(FramebufferTarget::Draw).GetBoundObject();
+            if (!readFbo || !drawFbo) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidOperation,
+                    MakeShared<GenericErrorInfo>("MG_Impl/GLImpl", __func__,
+                                                 "Read/draw framebuffer binding is null."));
+                return false;
+            }
+
+            if (!readFbo->CheckCompleteness() || !drawFbo->CheckCompleteness()) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidFramebufferOperation,
+                    MakeShared<GenericErrorInfo>("MG_Impl/GLImpl", __func__,
+                                                 "Read/draw framebuffer is incomplete."));
+                return false;
+            }
+
+            return true;
+        }
+
         void SampleMaski_State(GLuint maskNumber, GLbitfield mask) {
             // TODO: implement
         }
@@ -748,6 +811,9 @@ namespace MobileGL {
 
         void BlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0, GLint dstX1,
                              GLint dstY1, GLbitfield mask, GLenum filter) {
+            if (!BlitFramebuffer_State(srcX0, srcY0, srcX1, srcY1, dstX0, dstY0, dstX1, dstY1, mask, filter)) {
+                return;
+            }
             BlitFramebuffer_Backend(srcX0, srcY0, srcX1, srcY1, dstX0, dstY0, dstX1, dstY1, mask, filter);
         }
 

MobileGL/MG_Test/Backend/DirectVulkan/TestExec.cpp

@@ -132,6 +132,22 @@ int main() {
 
     MobileGL::MG_Initialize();
 
+    GLuint offscreenTex = 0;
+    GLuint offscreenFbo = 0;
+    glGenTextures(1, &offscreenTex);
+    glBindTexture(GL_TEXTURE_2D, offscreenTex);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 256, 256, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
+    glBindTexture(GL_TEXTURE_2D, 0);
+
+    glGenFramebuffers(1, &offscreenFbo);
+    glBindFramebuffer(GL_FRAMEBUFFER, offscreenFbo);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, offscreenTex, 0);
+    const GLenum offscreenFboStatus = glCheckFramebufferStatus(GL_FRAMEBUFFER);
+    std::cout << "Offscreen FBO status = 0x" << std::hex << offscreenFboStatus << std::dec << std::endl;
+    glBindFramebuffer(GL_FRAMEBUFFER, 0);
+
     GLuint vao = 0;
     glGenVertexArrays(1, &vao);
     glBindVertexArray(vao);
@@ -246,30 +262,30 @@ void main() {
     glBindBufferBase(GL_UNIFORM_BUFFER, 1, colorUbo);
     glBindBuffer(GL_UNIFORM_BUFFER, 0);
 
-    const auto startTime = std::chrono::steady_clock::now();
-
     int i = 0;
     while(!glfwWindowShouldClose(window)) {
         glfwPollEvents();
 
-        if (i % 1000 > 500)
+        const bool useOffscreenPath = ((i / 100) % 2) == 0;
+        if (useOffscreenPath) {
+            glBindFramebuffer(GL_FRAMEBUFFER, offscreenFbo);
             glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
-        else
+            glClear(GL_COLOR_BUFFER_BIT);
+
+            glBindFramebuffer(GL_READ_FRAMEBUFFER, offscreenFbo);
+            glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
+            glBlitFramebuffer(0, 0, 256, 256, 0, 0, 800, 600, GL_COLOR_BUFFER_BIT, GL_NEAREST);
+            glBindFramebuffer(GL_FRAMEBUFFER, 0);
+        } else {
+            glBindFramebuffer(GL_FRAMEBUFFER, 0);
             glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
             glClear(GL_COLOR_BUFFER_BIT);
-        if (i % 500 > 250) {
+        }
-            glUseProgram(program);
-            const auto now = std::chrono::steady_clock::now();
-            const float t = std::chrono::duration<float>(now - startTime).count();
-            glUniform1f(iTimeLocation, t);
 
-            uboColorData[0] = 0.5f + 0.5f * std::sin(t * 0.7f);
+        if (i % 100 == 0) {
-            uboColorData[1] = 0.5f + 0.5f * std::sin(t * 1.1f + 1.2f);
+            std::cout << "frame=" << i
-            uboColorData[2] = 0.5f + 0.5f * std::sin(t * 1.5f + 2.4f);
+                      << " path=" << (useOffscreenPath ? "offscreen-clear+blit" : "default-clear")
-            glBindBuffer(GL_UNIFORM_BUFFER, colorUbo);
+                      << std::endl;
-            glBufferSubData(GL_UNIFORM_BUFFER, 0, sizeof(uboColorData), uboColorData);
-            glBindBuffer(GL_UNIFORM_BUFFER, 0);
-            glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, nullptr);
         }
         eglSwapBuffers(display, surface);
         ++i;
@@ -281,6 +297,8 @@ void main() {
     glDeleteBuffers(1, &colorVbo);
     glDeleteBuffers(1, &ebo);
     glDeleteVertexArrays(1, &vao);
+    glDeleteFramebuffers(1, &offscreenFbo);
+    glDeleteTextures(1, &offscreenTex);
 
     glfwDestroyWindow(window);
 

MobileGL/MG_Util/ShaderTranspiler/ShaderCompiler.cpp

@@ -147,14 +147,13 @@ namespace MobileGL {
                 if (attrib.flags & ShaderCompileBits::CompileForOpenGL) {
                     tshader->setEnvInput(glslang::EShSourceGlsl, lang, glslang::EShClientVulkan, 450);
                     tshader->setEnvClient(glslang::EShClientOpenGL, glslang::EShTargetOpenGL_450);
-                    tshader->setEnvTarget(glslang::EShTargetSpv, glslang::EShTargetSpv_1_5);
+                    tshader->setEnvTarget(glslang::EShTargetSpv, glslang::EShTargetSpv_1_3);
                 } else {
                     tshader->setEnvInput(glslang::EShSourceGlsl, lang, glslang::EShClientVulkan, 450);
-                    tshader->setEnvClient(glslang::EShClientVulkan, glslang::EShTargetVulkan_1_3);
+                    // MobileGL runtime currently creates Vulkan 1.1 instance/device on Android path,
-                    tshader->setEnvTarget(glslang::EShTargetSpv,
+                    // so generated SPIR-V must not exceed SPIR-V 1.3.
-                                          ((attrib.flags & ShaderCompileBits::EmitDiscardAsDemote)
+                    tshader->setEnvClient(glslang::EShClientVulkan, glslang::EShTargetVulkan_1_1);
-                                               ? glslang::EShTargetSpv_1_6
+                    tshader->setEnvTarget(glslang::EShTargetSpv, glslang::EShTargetSpv_1_3);
-                                               : glslang::EShTargetSpv_1_5));
                     tshader->setEnvInputVulkanRulesRelaxed(); // using EXT_vulkan_glsl_relaxed for gl_VertexID and
                                                               // gl_InstanceID?
                 }
@@ -233,7 +232,7 @@ namespace MobileGL {
                 OptimizerOptions options;
                 options.set_run_validator(false);
 
-                Optimizer optimizer(SPV_ENV_UNIVERSAL_1_5);
+                Optimizer optimizer(SPV_ENV_VULKAN_1_1);
 
                 optimizer.RegisterPass(EliminateFloatEqualsZeroPass::CreateEliminateFloatEqualsZeroPass());