Reduce number of blits required in stereo 3D by tracking current eye...

src/rendering/gl/renderer/gl_postprocess.cpp

@@ -121,20 +121,11 @@ void FGLRenderer::BlurScene(float gameinfobluramount)
 	mBuffers->UpdateEffectTextures();
 
 	auto vrmode = VRMode::GetVRMode(true);
-	if (vrmode->mEyeCount == 1)
+	int eyeCount = vrmode->mEyeCount;
+	for (int i = 0; i < eyeCount; ++i)
 	{
 		mBuffers->RenderEffect("BlurScene");
-	}
-	else
-	{
-		for (int eye_ix = 0; eye_ix < vrmode->mEyeCount; ++eye_ix)
-		{
-			FGLDebug::PushGroup("EyeBlur");
-			mBuffers->BlitFromEyeTexture(eye_ix);
-			mBuffers->RenderEffect("BlurScene");
-			mBuffers->BlitToEyeTexture(eye_ix);
-			FGLDebug::PopGroup();
-		}
+		if (eyeCount - i > 1) mBuffers->NextEye(eyeCount);
 	}
 }
 
@@ -159,13 +150,12 @@ void FGLRenderer::Flush()
 	else
 	{
 		// Render 2D to eye textures
-		for (int eye_ix = 0; eye_ix < vrmode->mEyeCount; ++eye_ix)
+		int eyeCount = vrmode->mEyeCount;
+		for (int eye_ix = 0; eye_ix < eyeCount; ++eye_ix)
 		{
-			FGLDebug::PushGroup("Eye2D");
-			mBuffers->BlitFromEyeTexture(eye_ix);
 			screen->Draw2D();
-			mBuffers->BlitToEyeTexture(eye_ix);
-			FGLDebug::PopGroup();
+			if (eyeCount - eye_ix > 1)
+				mBuffers->NextEye(eyeCount);
 		}
 		screen->Clear2D();
 

src/rendering/gl/renderer/gl_renderbuffers.cpp

@@ -532,15 +532,15 @@ void FGLRenderBuffers::BlitSceneToTexture()
 //
 //==========================================================================
 
-void FGLRenderBuffers::BlitToEyeTexture(int eye)
+void FGLRenderBuffers::BlitToEyeTexture(int eye, bool allowInvalidate)
 {
 	CreateEyeBuffers(eye);
 
 	glBindFramebuffer(GL_READ_FRAMEBUFFER, mPipelineFB[mCurrentPipelineTexture].handle);
 	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, mEyeFBs[eye].handle);
 	glBlitFramebuffer(0, 0, mWidth, mHeight, 0, 0, mWidth, mHeight, GL_COLOR_BUFFER_BIT, GL_NEAREST);
 
-	if ((gl.flags & RFL_INVALIDATE_BUFFER) != 0)
+	if ((gl.flags & RFL_INVALIDATE_BUFFER) != 0 && allowInvalidate)
 	{
 		GLenum attachments[2] = { GL_COLOR_ATTACHMENT0, GL_DEPTH_STENCIL_ATTACHMENT };
 		glInvalidateFramebuffer(GL_READ_FRAMEBUFFER, 2, attachments);
@@ -552,7 +552,7 @@ void FGLRenderBuffers::BlitToEyeTexture(int eye)
 
 void FGLRenderBuffers::BlitFromEyeTexture(int eye)
 {
-	CreateEyeBuffers(eye);
+	if (mEyeFBs.Size() <= unsigned(eye)) return;
 
 	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, mPipelineFB[mCurrentPipelineTexture].handle);
 	glBindFramebuffer(GL_READ_FRAMEBUFFER, mEyeFBs[eye].handle);
@@ -1002,4 +1002,17 @@ void FGLRenderBuffers::RenderEffect(const FString &name)
 	FGLDebug::PopGroup();
 }
 
-}
+
+// Store the current stereo 3D eye buffer, and Load the next one
+
+int FGLRenderBuffers::NextEye(int eyeCount)
+{
+	int nextEye = (mCurrentEye + 1) % eyeCount;
+	if (nextEye == mCurrentEye) return mCurrentEye;
+	BlitToEyeTexture(mCurrentEye);
+	mCurrentEye = nextEye;
+	BlitFromEyeTexture(mCurrentEye);
+	return mCurrentEye;
+}
+
+}  // namespace OpenGLRenderer

src/rendering/gl/renderer/gl_renderbuffers.h

@@ -87,9 +87,11 @@ class FGLRenderBuffers
 
 	void BindOutputFB();
 
-	void BlitToEyeTexture(int eye);
+	void BlitToEyeTexture(int eye, bool allowInvalidate=true);
 	void BlitFromEyeTexture(int eye);
 	void BindEyeTexture(int eye, int texunit);
+	int NextEye(int eyeCount);
+	int & CurrentEye() { return mCurrentEye; }
 
 	void BindDitherTexture(int texunit);
 
@@ -156,6 +158,7 @@ class FGLRenderBuffers
 	// Eye buffers
 	TArray<PPGLTexture> mEyeTextures;
 	TArray<PPGLFrameBuffer> mEyeFBs;
+	int mCurrentEye = 0;
 
 	// Shadow map texture
 	PPGLTexture mShadowMapTexture;

src/rendering/gl/renderer/gl_scene.cpp

@@ -163,9 +163,11 @@ sector_t * FGLRenderer::RenderViewpoint (FRenderViewpoint &mainvp, AActor * came
     // Render (potentially) multiple views for stereo 3d
 	// Fixme. The view offsetting should be done with a static table and not require setup of the entire render state for the mode.
 	auto vrmode = VRMode::GetVRMode(mainview && toscreen);
-	for (int eye_ix = 0; eye_ix < vrmode->mEyeCount; ++eye_ix)
+	const int eyeCount = vrmode->mEyeCount;
+	mBuffers->CurrentEye() = 0;  // always begin at zero, in case eye count changed
+	for (int eye_ix = 0; eye_ix < eyeCount; ++eye_ix)
 	{
-		const auto &eye = vrmode->mEyes[eye_ix];
+		const auto &eye = vrmode->mEyes[mBuffers->CurrentEye()];
 		screen->SetViewportRects(bounds);
 
 		if (mainview) // Bind the scene frame buffer and turn on draw buffers used by ssao
@@ -218,8 +220,8 @@ sector_t * FGLRenderer::RenderViewpoint (FRenderViewpoint &mainvp, AActor * came
 			PostProcess.Unclock();
 		}
 		di->EndDrawInfo();
-		if (vrmode->mEyeCount > 1)
-			mBuffers->BlitToEyeTexture(eye_ix);
+		if (eyeCount - eye_ix > 1)
+			mBuffers->NextEye(eyeCount);
 	}
 
 	return mainvp.sector;

src/rendering/gl/renderer/gl_stereo3d.cpp

@@ -327,6 +327,12 @@ void FGLRenderer::PresentQuadStereo()
 
 void FGLRenderer::PresentStereo()
 {
+	auto vrmode = VRMode::GetVRMode(true);
+	const int eyeCount = vrmode->mEyeCount;
+	// Don't invalidate the bound framebuffer (..., false)
+	if (eyeCount > 1)
+		mBuffers->BlitToEyeTexture(mBuffers->CurrentEye(), false);
+
 	switch (vr_mode)
 	{
 	default: