Phase 4 step 1

apps/LoopThroughWithOpenGLCompositing/gl/RenderEngine.cpp

@@ -195,9 +195,15 @@ bool RenderEngine::TryPresentPreview(bool force, unsigned previewFps, unsigned o
 	if (!TryEnterCriticalSection(&mMutex))
 		return false;
 
+	const bool presented = PresentPreviewOnRenderThread(outputFrameWidth, outputFrameHeight);
+	LeaveCriticalSection(&mMutex);
+	return presented;
+}
+
+bool RenderEngine::PresentPreviewOnRenderThread(unsigned outputFrameWidth, unsigned outputFrameHeight)
+{
 	mRenderer.PresentToWindow(mHdc, outputFrameWidth, outputFrameHeight);
 	mLastPreviewPresentTime = std::chrono::steady_clock::now();
-	LeaveCriticalSection(&mMutex);
 	return true;
 }
 
@@ -206,12 +212,19 @@ bool RenderEngine::TryUploadInputFrame(const VideoIOFrame& inputFrame, const Vid
 	if (inputFrame.hasNoInputSource || inputFrame.bytes == nullptr)
 		return true;
 
-	const long textureSize = inputFrame.rowBytes * static_cast<long>(inputFrame.height);
 	if (!TryEnterCriticalSection(&mMutex))
 		return false;
 
 	wglMakeCurrent(mHdc, mHglrc);
+	const bool uploaded = UploadInputFrameOnRenderThread(inputFrame, videoState);
+	wglMakeCurrent(NULL, NULL);
+	LeaveCriticalSection(&mMutex);
+	return uploaded;
+}
 
+bool RenderEngine::UploadInputFrameOnRenderThread(const VideoIOFrame& inputFrame, const VideoIOState& videoState)
+{
+	const long textureSize = inputFrame.rowBytes * static_cast<long>(inputFrame.height);
 	glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
 	glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
 	glBindBuffer(GL_PIXEL_UNPACK_BUFFER, mRenderer.TextureUploadBuffer());
@@ -224,8 +237,6 @@ bool RenderEngine::TryUploadInputFrame(const VideoIOFrame& inputFrame, const Vid
 	glBindTexture(GL_TEXTURE_2D, 0);
 	glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
 
-	wglMakeCurrent(NULL, NULL);
-	LeaveCriticalSection(&mMutex);
 	return true;
 }
 
@@ -233,12 +244,17 @@ bool RenderEngine::RenderOutputFrame(const RenderPipelineFrameContext& context,
 {
 	EnterCriticalSection(&mMutex);
 	wglMakeCurrent(mHdc, mHglrc);
-	const bool rendered = mRenderPipeline.RenderFrame(context, outputFrame);
+	const bool rendered = RenderOutputFrameOnRenderThread(context, outputFrame);
 	wglMakeCurrent(NULL, NULL);
 	LeaveCriticalSection(&mMutex);
 	return rendered;
 }
 
+bool RenderEngine::RenderOutputFrameOnRenderThread(const RenderPipelineFrameContext& context, VideoIOOutputFrame& outputFrame)
+{
+	return mRenderPipeline.RenderFrame(context, outputFrame);
+}
+
 bool RenderEngine::ResolveRenderFrameState(
 	const RenderFrameInput& input,
 	std::vector<OscOverlayCommitRequest>* commitRequests,
@@ -297,14 +313,11 @@ void RenderEngine::RenderLayerStack(
 		});
 }
 
-bool RenderEngine::ReadOutputFrameRgba(unsigned width, unsigned height, std::vector<unsigned char>& bottomUpPixels)
+bool RenderEngine::ReadOutputFrameRgbaOnRenderThread(unsigned width, unsigned height, std::vector<unsigned char>& bottomUpPixels)
 {
 	if (width == 0 || height == 0)
 		return false;
 
-	EnterCriticalSection(&mMutex);
-	wglMakeCurrent(mHdc, mHglrc);
-
 	bottomUpPixels.resize(static_cast<std::size_t>(width) * height * 4);
 	glBindFramebuffer(GL_READ_FRAMEBUFFER, mRenderer.OutputFramebuffer());
 	glReadBuffer(GL_COLOR_ATTACHMENT0);
@@ -313,15 +326,23 @@ bool RenderEngine::ReadOutputFrameRgba(unsigned width, unsigned height, std::vec
 	glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, bottomUpPixels.data());
 	glPixelStorei(GL_PACK_ALIGNMENT, 4);
 
-	wglMakeCurrent(NULL, NULL);
-	LeaveCriticalSection(&mMutex);
 	return true;
 }
 
 bool RenderEngine::CaptureOutputFrameRgbaTopDown(unsigned width, unsigned height, std::vector<unsigned char>& topDownPixels)
+{
+	EnterCriticalSection(&mMutex);
+	wglMakeCurrent(mHdc, mHglrc);
+	const bool captured = CaptureOutputFrameRgbaTopDownOnRenderThread(width, height, topDownPixels);
+	wglMakeCurrent(NULL, NULL);
+	LeaveCriticalSection(&mMutex);
+	return captured;
+}
+
+bool RenderEngine::CaptureOutputFrameRgbaTopDownOnRenderThread(unsigned width, unsigned height, std::vector<unsigned char>& topDownPixels)
 {
 	std::vector<unsigned char> bottomUpPixels;
-	if (!ReadOutputFrameRgba(width, height, bottomUpPixels))
+	if (!ReadOutputFrameRgbaOnRenderThread(width, height, bottomUpPixels))
 		return false;
 
 	topDownPixels.resize(bottomUpPixels.size());

apps/LoopThroughWithOpenGLCompositing/gl/RenderEngine.h

@@ -118,10 +118,15 @@ public:
 		unsigned captureTextureWidth,
 		VideoIOPixelFormat inputPixelFormat,
 		unsigned historyCap);
-	bool ReadOutputFrameRgba(unsigned width, unsigned height, std::vector<unsigned char>& bottomUpPixels);
 	bool CaptureOutputFrameRgbaTopDown(unsigned width, unsigned height, std::vector<unsigned char>& topDownPixels);
 
 private:
+	bool PresentPreviewOnRenderThread(unsigned outputFrameWidth, unsigned outputFrameHeight);
+	bool UploadInputFrameOnRenderThread(const VideoIOFrame& inputFrame, const VideoIOState& videoState);
+	bool RenderOutputFrameOnRenderThread(const RenderPipelineFrameContext& context, VideoIOOutputFrame& outputFrame);
+	bool ReadOutputFrameRgbaOnRenderThread(unsigned width, unsigned height, std::vector<unsigned char>& bottomUpPixels);
+	bool CaptureOutputFrameRgbaTopDownOnRenderThread(unsigned width, unsigned height, std::vector<unsigned char>& topDownPixels);
+
 	OpenGLRenderer mRenderer;
 	OpenGLRenderPass mRenderPass;
 	OpenGLRenderPipeline mRenderPipeline;

docs/PHASE_4_RENDER_THREAD_OWNERSHIP_DESIGN.md

@@ -7,12 +7,12 @@ Phase 1 named the subsystems. Phase 2 added the typed event substrate. Phase 3 m
 ## Status
 
 - Phase 4 design package: proposed.
-- Phase 4 implementation: not started.
+- Phase 4 implementation: Step 1 started. The existing synchronous `RenderEngine` entrypoints now delegate their GL bodies to named `...OnRenderThread(...)` helpers, but no command queue or dedicated render thread exists yet.
 - Current alignment: the repo has a named frame-state contract and cleaner render-state preparation, but GL work is still entered through multiple paths protected by one shared `CRITICAL_SECTION`.
 
 Current GL ownership footholds:
 
-- `RenderEngine` owns GL resources and the current context-binding helpers.
+- `RenderEngine` owns GL resources, the current context-binding compatibility shims, and named render-thread helper methods.
 - `RenderFrameInput` / `RenderFrameState` provide the frame-state contract that a render thread can consume.
 - `RenderFrameStateResolver` prepares the render-facing layer state before drawing.
 - `OpenGLVideoIOBridge` still calls `RenderEngine::TryUploadInputFrame(...)` from the input path and `RenderEngine::RenderOutputFrame(...)` from the output path.
@@ -64,10 +64,10 @@ The current code paths that matter most are:
 
 | Entry point | Current behavior | Phase 4 direction |
 | --- | --- | --- |
-| `RenderEngine::TryUploadInputFrame(...)` | attempts to take the GL lock, binds the context, uploads input texture | enqueue latest input frame; render thread uploads |
-| `RenderEngine::RenderOutputFrame(...)` | takes the GL lock, binds the context, renders, packs/readbacks output | render thread executes output frame production |
-| `RenderEngine::TryPresentPreview(...)` | attempts to take the GL lock and presents preview | render thread or preview presenter consumes latest completed frame |
-| `RenderEngine::CaptureOutputFrameRgbaTopDown(...)` | takes the GL lock and reads output pixels | screenshot request becomes render-thread command |
+| `RenderEngine::TryUploadInputFrame(...)` | attempts to take the GL lock, binds the context, delegates upload to `UploadInputFrameOnRenderThread(...)` | enqueue latest input frame; render thread uploads |
+| `RenderEngine::RenderOutputFrame(...)` | takes the GL lock, binds the context, delegates render/readback to `RenderOutputFrameOnRenderThread(...)` | render thread executes output frame production |
+| `RenderEngine::TryPresentPreview(...)` | attempts to take the GL lock and delegates presentation to `PresentPreviewOnRenderThread(...)` | render thread or preview presenter consumes latest completed frame |
+| `RenderEngine::CaptureOutputFrameRgbaTopDown(...)` | takes the GL lock, binds the context, delegates readback to `CaptureOutputFrameRgbaTopDownOnRenderThread(...)` | screenshot request becomes render-thread command |
 | `OpenGLVideoIOBridge::UploadInputFrame(...)` | calls render upload directly | push input frame into render queue/mailbox |
 | `OpenGLVideoIOBridge::RenderScheduledFrame(...)` | calls render output directly from backend path | request/consume render-produced output without callback-owned GL |
 
@@ -184,7 +184,7 @@ Render-thread-only methods should be private or clearly named:
 
 - `RenderEngine::UploadInputFrameOnRenderThread(...)`
 - `RenderEngine::RenderOutputFrameOnRenderThread(...)`
-- `RenderEngine::CaptureOutputFrameOnRenderThread(...)`
+- `RenderEngine::CaptureOutputFrameRgbaTopDownOnRenderThread(...)`
 
 The current `TryUploadInputFrame`, `RenderOutputFrame`, `TryPresentPreview`, and `CaptureOutputFrameRgbaTopDown` methods can remain as compatibility shims during migration, but their implementations should move toward enqueue-and-wait or enqueue-and-return behavior instead of binding GL directly from the caller's thread.
 
@@ -214,9 +214,9 @@ Split existing direct GL methods into public request methods and private render-
 
 Initial target:
 
-- keep current synchronous behavior where callers need a result
-- move GL bodies into clearly render-thread-owned helpers
-- make future queue migration mechanical
+- [x] keep current synchronous behavior where callers need a result
+- [x] move GL bodies into clearly render-thread-owned helpers for upload, output render, preview presentation, and screenshot readback
+- [x] make future queue migration mechanical
 
 ### Step 2. Add Render Command Queue