[OpenGL] Add OpenGLPlatformInfo.SetSwapchainFramebuffer

This is used when a non-zero FBO represents the main swapchain framebuffer.

src/Veldrid/OpenGL/OpenGLCommandExecutor.cs

@@ -10,7 +10,8 @@ internal unsafe class OpenGLCommandExecutor
         private readonly GraphicsBackend _backend;
         private readonly OpenGLTextureSamplerManager _textureSamplerManager;
         private readonly StagingMemoryPool _stagingMemoryPool;
-        private OpenGLExtensions _extensions;
+        private readonly OpenGLExtensions _extensions;
+        private Action _setSwapchainFramebuffer;
 
         private Framebuffer _fb;
         private bool _isSwapchainFB;
@@ -34,12 +35,14 @@ internal unsafe class OpenGLCommandExecutor
             GraphicsBackend backend,
             OpenGLTextureSamplerManager textureSamplerManager,
             OpenGLExtensions extensions,
-            StagingMemoryPool stagingMemoryPool)
+            StagingMemoryPool stagingMemoryPool,
+            Action setSwapchainFramebuffer)
         {
             _backend = backend;
             _extensions = extensions;
             _textureSamplerManager = textureSamplerManager;
             _stagingMemoryPool = stagingMemoryPool;
+            _setSwapchainFramebuffer = setSwapchainFramebuffer;
         }
 
         public void Begin()
@@ -314,8 +317,16 @@ public void SetFramebuffer(Framebuffer fb)
             }
             else if (fb is OpenGLSwapchainFramebuffer)
             {
-                glBindFramebuffer(FramebufferTarget.Framebuffer, 0);
-                CheckLastError();
+                if (_setSwapchainFramebuffer != null)
+                {
+                    _setSwapchainFramebuffer();
+                }
+                else
+                {
+                    glBindFramebuffer(FramebufferTarget.Framebuffer, 0);
+                    CheckLastError();
+                }
+
                 _isSwapchainFB = true;
             }
             else

src/Veldrid/OpenGL/OpenGLGraphicsDevice.cs

@@ -163,7 +163,12 @@ public override bool SyncToVerticalBlank
             }
 
             _textureSamplerManager = new OpenGLTextureSamplerManager(_extensions);
-            _commandExecutor = new OpenGLCommandExecutor(_backendType, _textureSamplerManager, _extensions, _stagingMemoryPool);
+            _commandExecutor = new OpenGLCommandExecutor(
+                _backendType,
+                _textureSamplerManager,
+                _extensions,
+                _stagingMemoryPool,
+                platformInfo.SetSwapchainFramebuffer);
 
             int maxColorTextureSamples;
             glGetIntegerv(GetPName.MaxColorTextureSamples, &maxColorTextureSamples);

src/Veldrid/OpenGL/OpenGLPlatformInfo.cs

@@ -40,6 +40,11 @@ public class OpenGLPlatformInfo
         /// A delegate which can be used to set the synchronization behavior of the OpenGL context.
         /// </summary>
         public Action<bool> SetSyncToVerticalBlank { get; }
+        /// <summary>
+        /// A delegate which can be used to set the framebuffer used to render to the application Swapchain.
+        /// If this is null, the default FBO (0) will be bound.
+        /// </summary>
+        public Action SetSwapchainFramebuffer { get; }
 
         /// <summary>
         /// Constructs a new OpenGLPlatformInfo.
@@ -74,5 +79,43 @@ public class OpenGLPlatformInfo
             SwapBuffers = swapBuffers;
             SetSyncToVerticalBlank = setSyncToVerticalBlank;
         }
+
+        /// <summary>
+        /// Constructs a new OpenGLPlatformInfo.
+        /// </summary>
+        /// <param name="openGLContextHandle">The OpenGL context handle.</param>
+        /// <param name="getProcAddress">A delegate which can be used to retrieve OpenGL function pointers by name.</param>
+        /// <param name="makeCurrent">A delegate which can be used to make the given OpenGL context current on the calling
+        /// thread.</param>
+        /// <param name="getCurrentContext">A delegate which can be used to retrieve the calling thread's active OpenGL context.</param>
+        /// <param name="clearCurrentContext">A delegate which can be used to clear the calling thread's GL context.</param>
+        /// <param name="deleteContext">A delegate which can be used to delete the given context.</param>
+        /// <param name="swapBuffers">A delegate which can be used to swap the main back buffer associated with the OpenGL
+        /// context.</param>
+        /// <param name="setSyncToVerticalBlank">A delegate which can be used to set the synchronization behavior of the OpenGL
+        /// context.</param>
+        /// <param name="setSwapchainFramebuffer">A delegate which can be used to set the framebuffer used to render to the
+        /// application Swapchain.</param>
+        public OpenGLPlatformInfo(
+            IntPtr openGLContextHandle,
+            Func<string, IntPtr> getProcAddress,
+            Action<IntPtr> makeCurrent,
+            Func<IntPtr> getCurrentContext,
+            Action clearCurrentContext,
+            Action<IntPtr> deleteContext,
+            Action swapBuffers,
+            Action<bool> setSyncToVerticalBlank,
+            Action setSwapchainFramebuffer)
+        {
+            OpenGLContextHandle = openGLContextHandle;
+            GetProcAddress = getProcAddress;
+            MakeCurrent = makeCurrent;
+            GetCurrentContext = getCurrentContext;
+            ClearCurrentContext = clearCurrentContext;
+            DeleteContext = deleteContext;
+            SwapBuffers = swapBuffers;
+            SetSyncToVerticalBlank = setSyncToVerticalBlank;
+            SetSwapchainFramebuffer = setSwapchainFramebuffer;
+        }
     }
 }