Clear and InvalidateFramebuffer optimization

src/gl/scene/gl_scene.cpp

@@ -174,18 +174,18 @@ void FGLRenderer::Set3DViewport(bool mainview)
 		mBuffers->BindSceneFB();
 	}
 
+	// Always clear all buffers with scissor test disabled.
+	// This is faster on newer hardware because it allows the GPU to skip
+	// reading from slower memory where the full buffers are stored.
+	glDisable(GL_SCISSOR_TEST);
+	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
+	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+
 	const auto &bounds = mSceneViewport;
 	glViewport(bounds.left, bounds.top, bounds.width, bounds.height);
 	glScissor(bounds.left, bounds.top, bounds.width, bounds.height);
 
 	glEnable(GL_SCISSOR_TEST);
-	
-	#ifdef _DEBUG
-		glClearColor(0.0f, 0.0f, 0.0f, 0.0f); 
-		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
-	#else
-		glClear(GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
-	#endif
 
 	glEnable(GL_MULTISAMPLE);
 	glEnable(GL_DEPTH_TEST);

src/gl/system/gl_interface.cpp

@@ -244,6 +244,8 @@ void gl_LoadExtensions()
 		gl.buffermethod = BM_PERSISTENT;
 	}
 
+	if (gl.version >= 4.3f || CheckExtension("GL_ARB_invalidate_subdata")) gl.flags |= RFL_INVALIDATE_BUFFER;
+
 	const char *lm = Args->CheckValue("-lightmethod");
 	if (lm != NULL)
 	{

src/gl/system/gl_interface.h

@@ -23,7 +23,9 @@ enum RenderFlags
 
 	RFL_NO_RGBA16F = 32,
 	RFL_NO_DEPTHSTENCIL = 64,
-	RFL_NO_CLIP_PLANES = 128
+	RFL_NO_CLIP_PLANES = 128,
+
+	RFL_INVALIDATE_BUFFER = 256
 };
 
 enum TexMode