OpenGL backend: enabled handling of default framebuffer in render passes

2 files changed, 70 insertions, 12 deletions

diff --git a/Graphics/GraphicsEngineOpenGL/src/DeviceContextGLImpl.cpp b/Graphics/GraphicsEngineOpenGL/src/DeviceContextGLImpl.cpp
index 37e4a3f4..3b3122bf 100644
--- a/Graphics/GraphicsEngineOpenGL/src/DeviceContextGLImpl.cpp
+++ b/Graphics/GraphicsEngineOpenGL/src/DeviceContextGLImpl.cpp
@@ -424,6 +424,22 @@ void DeviceContextGLImpl::BeginSubpass()
     VERIFY_EXPR(m_SubpassIndex < RPDesc.SubpassCount);
     const auto& SubpassDesc = RPDesc.pSubpasses[m_SubpassIndex];
     const auto& FBDesc      = m_pBoundFramebuffer->GetDesc();
+
+    const auto& RenderTargetFBO = m_pBoundFramebuffer->GetSubpassFramebuffer(m_SubpassIndex).RenderTarget;
+    if (RenderTargetFBO != 0)
+    {
+        m_ContextState.BindFBO(RenderTargetFBO);
+    }
+    else
+    {
+        GLuint DefaultFBOHandle = m_pSwapChain->GetDefaultFBO();
+        if (m_DefaultFBO != DefaultFBOHandle)
+        {
+            m_DefaultFBO = GLObjectWrappers::GLFrameBufferObj{true, GLObjectWrappers::GLFBOCreateReleaseHelper(DefaultFBOHandle)};
+        }
+        m_ContextState.BindFBO(m_DefaultFBO);
+    }
+
     for (Uint32 rt = 0; rt < SubpassDesc.RenderTargetAttachmentCount; ++rt)
     {
         const auto& RTAttachmentRef = SubpassDesc.pRenderTargetAttachments[rt];
@@ -464,8 +480,8 @@ void DeviceContextGLImpl::EndSubpass()
     {
         const auto& SubpassFBOs = m_pBoundFramebuffer->GetSubpassFramebuffer(m_SubpassIndex);
 
-        glBindFramebuffer(GL_DRAW_FRAMEBUFFER, SubpassFBOs.RenderTarget);
-        DEV_CHECK_GL_ERROR("Failed to bind subpass render target FBO as draw framebuffer");
+        glBindFramebuffer(GL_READ_FRAMEBUFFER, SubpassFBOs.RenderTarget);
+        DEV_CHECK_GL_ERROR("Failed to bind subpass render target FBO as read framebuffer");
 
         GLuint ResolveDstFBO = SubpassFBOs.Resolve;
         if (ResolveDstFBO == 0)
@@ -481,7 +497,7 @@ void DeviceContextGLImpl::EndSubpass()
                           GL_COLOR_BUFFER_BIT,
                           GL_NEAREST // Filter is ignored
         );
-        DEV_CHECK_GL_ERROR("glBlitFramebuffer() failed when resolving multi-sampled texture");
+        DEV_CHECK_GL_ERROR("glBlitFramebuffer() failed when resolving multi-sampled attachments");
     }
     m_ContextState.InvalidateFBO();
 }
@@ -495,7 +511,7 @@ void DeviceContextGLImpl::BeginRenderPass(const BeginRenderPassAttribs& Attribs)
         m_AttachmentClearValues[i] = Attribs.pClearValues[i];
 
     VERIFY_EXPR(m_pBoundFramebuffer);
-    m_ContextState.BindFBO(m_pBoundFramebuffer->GetSubpassFramebuffer(m_SubpassIndex).RenderTarget);
+
     SetViewports(1, nullptr, 0, 0);
 
     BeginSubpass();
@@ -504,20 +520,14 @@ void DeviceContextGLImpl::BeginRenderPass(const BeginRenderPassAttribs& Attribs)
 void DeviceContextGLImpl::NextSubpass()
 {
     EndSubpass();
-
     TDeviceContextBase::NextSubpass();
-
-    m_ContextState.BindFBO(m_pBoundFramebuffer->GetSubpassFramebuffer(m_SubpassIndex).RenderTarget);
-
     BeginSubpass();
 }
 
 void DeviceContextGLImpl::EndRenderPass()
 {
     EndSubpass();
-
     TDeviceContextBase::EndRenderPass();
-
     m_ContextState.InvalidateFBO();
 }
 
diff --git a/Graphics/GraphicsEngineOpenGL/src/FramebufferGLImpl.cpp b/Graphics/GraphicsEngineOpenGL/src/FramebufferGLImpl.cpp
index 51abf1ba..c84d9816 100644
--- a/Graphics/GraphicsEngineOpenGL/src/FramebufferGLImpl.cpp
+++ b/Graphics/GraphicsEngineOpenGL/src/FramebufferGLImpl.cpp
@@ -34,6 +34,50 @@
 namespace Diligent
 {
 
+static bool UseDefaultFBO(Uint32             NumRenderTargets,
+                          TextureViewGLImpl* ppRTVs[],
+                          TextureViewGLImpl* pDSV)
+{
+    bool useDefaultFBO = false;
+    for (Uint32 rt = 0; rt < NumRenderTargets; ++rt)
+    {
+        if (ppRTVs[rt] != nullptr && ppRTVs[rt]->GetHandle() == 0)
+        {
+            if (rt == 0)
+            {
+                useDefaultFBO = true;
+            }
+            else
+            {
+                LOG_ERROR_AND_THROW("In OpenGL, swap chain back buffer can be the only render target in the framebuffer "
+                                    "and cannot be combined with any other render target.");
+            }
+        }
+    }
+
+    if (pDSV != nullptr)
+    {
+        if (useDefaultFBO && pDSV->GetHandle() != 0)
+        {
+            LOG_ERROR_AND_THROW("In OpenGL, swap chain back buffer can only be paired with the default depth-stencil buffer.");
+        }
+
+        if (pDSV->GetHandle() == 0)
+        {
+            if (!useDefaultFBO && NumRenderTargets > 0)
+            {
+                LOG_ERROR_AND_THROW("In OpenGL, the swap chain's depth-stencil buffer can only be paired with its back buffer.");
+            }
+            else
+            {
+                useDefaultFBO = true;
+            }
+        }
+    }
+
+    return useDefaultFBO;
+}
+
 FramebufferGLImpl::FramebufferGLImpl(IReferenceCounters*    pRefCounters,
                                      RenderDeviceGLImpl*    pDevice,
                                      GLContextState&        CtxState,
@@ -62,7 +106,9 @@ FramebufferGLImpl::FramebufferGLImpl(IReferenceCounters*    pRefCounters,
         {
             pDSV = ValidatedCast<TextureViewGLImpl>(m_Desc.ppAttachments[SubpassDesc.pDepthStencilAttachment->AttachmentIndex]);
         }
-        auto RenderTargetFBO = FBOCache::CreateFBO(CtxState, SubpassDesc.RenderTargetAttachmentCount, ppRTVs, pDSV);
+        auto RenderTargetFBO = UseDefaultFBO(SubpassDesc.RenderTargetAttachmentCount, ppRTVs, pDSV) ?
+            GLObjectWrappers::GLFrameBufferObj{false} :
+            FBOCache::CreateFBO(CtxState, SubpassDesc.RenderTargetAttachmentCount, ppRTVs, pDSV);
 
         GLObjectWrappers::GLFrameBufferObj ResolveFBO{false};
         if (SubpassDesc.pResolveAttachments != nullptr)
@@ -76,7 +122,9 @@ FramebufferGLImpl::FramebufferGLImpl(IReferenceCounters*    pRefCounters,
                     ppRsvlViews[rt] = ValidatedCast<TextureViewGLImpl>(m_Desc.ppAttachments[RslvAttachmentRef.AttachmentIndex]);
                 }
             }
-            ResolveFBO = FBOCache::CreateFBO(CtxState, SubpassDesc.RenderTargetAttachmentCount, ppRsvlViews, nullptr);
+            ResolveFBO = UseDefaultFBO(SubpassDesc.RenderTargetAttachmentCount, ppRsvlViews, nullptr) ?
+                GLObjectWrappers::GLFrameBufferObj{false} :
+                FBOCache::CreateFBO(CtxState, SubpassDesc.RenderTargetAttachmentCount, ppRsvlViews, nullptr);
         }
 
         m_SubpassFramebuffers.emplace_back(std::move(RenderTargetFBO), std::move(ResolveFBO));