diff --git a/src/gl/data/gl_vertexbuffer.cpp b/src/gl/data/gl_vertexbuffer.cpp
index 7e77849545..31cb8d0b5c 100644
--- a/src/gl/data/gl_vertexbuffer.cpp
+++ b/src/gl/data/gl_vertexbuffer.cpp
@@ -126,6 +126,7 @@ void FSimpleVertexBuffer::EnableColorArray(bool on)
 void FSimpleVertexBuffer::set(FSimpleVertex *verts, int count)
 {
 	glBindBuffer(GL_ARRAY_BUFFER, vbo_id);
+	gl_RenderState.ResetVertexBuffer();
 	gl_RenderState.SetVertexBuffer(this);
 	glBufferData(GL_ARRAY_BUFFER, count * sizeof(*verts), verts, GL_STREAM_DRAW);
 }
@@ -139,18 +140,32 @@ void FSimpleVertexBuffer::set(FSimpleVertex *verts, int count)
 FFlatVertexBuffer::FFlatVertexBuffer(int width, int height)
 : FVertexBuffer(gl.buffermethod != BM_CLIENTARRAY)
 {
-	if (gl.buffermethod != BM_CLIENTARRAY)
+	switch (gl.buffermethod)
+	{
+	case BM_PERSISTENT:
 	{
 		unsigned int bytesize = BUFFER_SIZE * sizeof(FFlatVertex);
 		glBindBuffer(GL_ARRAY_BUFFER, vbo_id);
 		glBufferStorage(GL_ARRAY_BUFFER, bytesize, NULL, GL_MAP_WRITE_BIT | GL_MAP_PERSISTENT_BIT | GL_MAP_COHERENT_BIT);
 		map = (FFlatVertex*)glMapBufferRange(GL_ARRAY_BUFFER, 0, bytesize, GL_MAP_WRITE_BIT | GL_MAP_PERSISTENT_BIT | GL_MAP_COHERENT_BIT);
+		break;
 	}
-	else
+
+	case BM_DEFERRED:
+	{
+		unsigned int bytesize = BUFFER_SIZE * sizeof(FFlatVertex);
+		glBindBuffer(GL_ARRAY_BUFFER, vbo_id);
+		glBufferData(GL_ARRAY_BUFFER, bytesize, NULL, GL_STREAM_DRAW);
+		map = nullptr;
+		break;
+	}
+
+	case BM_CLIENTARRAY:
 	{
 		// The fallback path uses immediate mode rendering and does not set up an actual vertex buffer
-		vbo_shadowdata.Reserve(BUFFER_SIZE);
 		map = new FFlatVertex[BUFFER_SIZE];
+		break;
+	}
 	}
 	mIndex = mCurIndex = 0;
 	mNumReserved = NUM_RESERVED;
@@ -185,6 +200,13 @@ FFlatVertexBuffer::FFlatVertexBuffer(int width, int height)
 	vbo_shadowdata[18].Set(32767.0f, -32767.0f, 32767.0f, 0, 0);
 	vbo_shadowdata[19].Set(32767.0f, -32767.0f, -32767.0f, 0, 0);
 
+	if (gl.buffermethod == BM_DEFERRED)
+	{
+		Map();
+		memcpy(map, &vbo_shadowdata[0], mNumReserved * sizeof(FFlatVertex));
+		Unmap();
+	}
+
 }
 
 FFlatVertexBuffer::~FFlatVertexBuffer()
@@ -195,7 +217,7 @@ FFlatVertexBuffer::~FFlatVertexBuffer()
 		glUnmapBuffer(GL_ARRAY_BUFFER);
 		glBindBuffer(GL_ARRAY_BUFFER, 0);
 	}
-	else
+	if (gl.buffermethod == BM_CLIENTARRAY)
 	{
 		delete[] map;
 	}
@@ -208,7 +230,7 @@ void FFlatVertexBuffer::BindVBO()
 	glBindBuffer(GL_ARRAY_BUFFER, vbo_id);
 	if (gl.glslversion > 0)
 	{
-		if (vbo_id != 0)	// set this up only if there is an actual buffer.
+		if (gl.buffermethod != BM_CLIENTARRAY)
 		{
 			glVertexAttribPointer(VATTR_VERTEX, 3, GL_FLOAT, false, sizeof(FFlatVertex), &VTO->x);
 			glVertexAttribPointer(VATTR_TEXCOORD, 2, GL_FLOAT, false, sizeof(FFlatVertex), &VTO->u);
@@ -226,12 +248,37 @@ void FFlatVertexBuffer::BindVBO()
 	}
 	else
 	{
-		glDisableClientState(GL_VERTEX_ARRAY);
-		glDisableClientState(GL_TEXTURE_COORD_ARRAY);
+		glVertexPointer(3, GL_FLOAT, sizeof(FFlatVertex), &map->x);
+		glTexCoordPointer(2, GL_FLOAT, sizeof(FFlatVertex), &map->u);
+		glEnableClientState(GL_VERTEX_ARRAY);
+		glEnableClientState(GL_TEXTURE_COORD_ARRAY);
 		glDisableClientState(GL_COLOR_ARRAY);
 	}
 }
 
+void FFlatVertexBuffer::Map()
+{
+	if (gl.buffermethod == BM_DEFERRED)
+	{
+		unsigned int bytesize = BUFFER_SIZE * sizeof(FFlatVertex);
+		glBindBuffer(GL_ARRAY_BUFFER, vbo_id);
+		gl_RenderState.ResetVertexBuffer();
+		map = (FFlatVertex*)glMapBufferRange(GL_ARRAY_BUFFER, 0, bytesize, GL_MAP_WRITE_BIT|GL_MAP_UNSYNCHRONIZED_BIT);
+	}
+}
+
+void FFlatVertexBuffer::Unmap()
+{
+	if (gl.buffermethod == BM_DEFERRED)
+	{
+		unsigned int bytesize = BUFFER_SIZE * sizeof(FFlatVertex);
+		glBindBuffer(GL_ARRAY_BUFFER, vbo_id);
+		gl_RenderState.ResetVertexBuffer();
+		glUnmapBuffer(GL_ARRAY_BUFFER);
+		map = nullptr;
+	}
+}
+
 //==========================================================================
 //
 // Initialize a single vertex
@@ -412,7 +459,9 @@ void FFlatVertexBuffer::CreateVBO()
 	vbo_shadowdata.Resize(mNumReserved);
 	CreateFlatVBO();
 	mCurIndex = mIndex = vbo_shadowdata.Size();
+	Map();
 	memcpy(map, &vbo_shadowdata[0], vbo_shadowdata.Size() * sizeof(FFlatVertex));
+	Unmap();
 }
 
 //==========================================================================
diff --git a/src/gl/data/gl_vertexbuffer.h b/src/gl/data/gl_vertexbuffer.h
index 68f1013675..88a1de2b89 100644
--- a/src/gl/data/gl_vertexbuffer.h
+++ b/src/gl/data/gl_vertexbuffer.h
@@ -149,6 +149,9 @@ public:
 		mCurIndex = mIndex;
 	}
 
+	void Map();
+	void Unmap();
+
 private:
 	int CreateSubsectorVertices(subsector_t *sub, const secplane_t &plane, int floor);
 	int CreateSectorVertices(sector_t *sec, const secplane_t &plane, int floor);
diff --git a/src/gl/renderer/gl_postprocess.cpp b/src/gl/renderer/gl_postprocess.cpp
index 20f6f469f4..3a83f4caf5 100644
--- a/src/gl/renderer/gl_postprocess.cpp
+++ b/src/gl/renderer/gl_postprocess.cpp
@@ -114,7 +114,7 @@ void FGLRenderer::RenderScreenQuad()
 {
 	mVBO->BindVBO();
 	gl_RenderState.ResetVertexBuffer();
-	glDrawArrays(GL_TRIANGLE_STRIP, FFlatVertexBuffer::PRESENT_INDEX, 4);
+	GLRenderer->mVBO->RenderArray(GL_TRIANGLE_STRIP, FFlatVertexBuffer::PRESENT_INDEX, 4);
 }
 
 //-----------------------------------------------------------------------------
diff --git a/src/gl/scene/gl_portal.cpp b/src/gl/scene/gl_portal.cpp
index 4b8d8eb275..cd3efb9e3b 100644
--- a/src/gl/scene/gl_portal.cpp
+++ b/src/gl/scene/gl_portal.cpp
@@ -163,8 +163,8 @@ void GLPortal::DrawPortalStencil()
 	}
 	if (NeedCap() && lines.Size() > 1)
 	{
-		glDrawArrays(GL_TRIANGLE_FAN, FFlatVertexBuffer::STENCILTOP_INDEX, 4);
-		glDrawArrays(GL_TRIANGLE_FAN, FFlatVertexBuffer::STENCILBOTTOM_INDEX, 4);
+		GLRenderer->mVBO->RenderArray(GL_TRIANGLE_FAN, FFlatVertexBuffer::STENCILTOP_INDEX, 4);
+		GLRenderer->mVBO->RenderArray(GL_TRIANGLE_FAN, FFlatVertexBuffer::STENCILBOTTOM_INDEX, 4);
 	}
 }
 
@@ -1178,9 +1178,9 @@ void GLHorizonPortal::DrawContents()
 
 	for (unsigned i = 0; i < vcount; i += 4)
 	{
-		glDrawArrays(GL_TRIANGLE_STRIP, voffset + i, 4);
+		GLRenderer->mVBO->RenderArray(GL_TRIANGLE_STRIP, voffset + i, 4);
 	}
-	glDrawArrays(GL_TRIANGLE_STRIP, voffset + vcount, 10);
+	GLRenderer->mVBO->RenderArray(GL_TRIANGLE_STRIP, voffset + vcount, 10);
 
 	gl_RenderState.EnableTextureMatrix(false);
 	PortalAll.Unclock();
diff --git a/src/gl/scene/gl_scene.cpp b/src/gl/scene/gl_scene.cpp
index 250ec0c532..08591283c0 100644
--- a/src/gl/scene/gl_scene.cpp
+++ b/src/gl/scene/gl_scene.cpp
@@ -284,6 +284,7 @@ void FGLRenderer::CreateScene()
 	for(unsigned i=0;i<portals.Size(); i++) portals[i]->glportal = NULL;
 	gl_spriteindex=0;
 	Bsp.Clock();
+	GLRenderer->mVBO->Map();
 	R_SetView();
 	validcount++;	// used for processing sidedefs only once by the renderer.
 	gl_RenderBSPNode (nodes + numnodes - 1);
@@ -295,6 +296,7 @@ void FGLRenderer::CreateScene()
 	gl_drawinfo->HandleMissingTextures();	// Missing upper/lower textures
 	gl_drawinfo->HandleHackedSubsectors();	// open sector hacks for deep water
 	gl_drawinfo->ProcessSectorStacks();		// merge visplanes of sector stacks
+	GLRenderer->mVBO->Unmap();
 
 	ProcessAll.Unclock();
 
@@ -525,7 +527,7 @@ void gl_FillScreen()
 	gl_RenderState.EnableTexture(false);
 	gl_RenderState.Apply();
 	// The fullscreen quad is stored at index 4 in the main vertex buffer.
-	glDrawArrays(GL_TRIANGLE_STRIP, FFlatVertexBuffer::FULLSCREEN_INDEX, 4);
+	GLRenderer->mVBO->RenderArray(GL_TRIANGLE_STRIP, FFlatVertexBuffer::FULLSCREEN_INDEX, 4);
 }
 
 //==========================================================================
diff --git a/src/gl/shaders/gl_shader.cpp b/src/gl/shaders/gl_shader.cpp
index 67b9a2d6ae..8ac2b70933 100644
--- a/src/gl/shaders/gl_shader.cpp
+++ b/src/gl/shaders/gl_shader.cpp
@@ -125,7 +125,7 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 			vp_comb = "#version 400 core\n#extension GL_ARB_shader_storage_buffer_object : require\n#define SHADER_STORAGE_LIGHTS\n";
 		}
 	}
-	//if (gl.buffermethod == BM_DEFERRED)
+	if (gl.buffermethod == BM_DEFERRED)
 	{
 		vp_comb << "#define USE_QUAD_DRAWER\n";
 	}
diff --git a/src/gl/system/gl_interface.cpp b/src/gl/system/gl_interface.cpp
index a7b1be6487..9eb1d779e5 100644
--- a/src/gl/system/gl_interface.cpp
+++ b/src/gl/system/gl_interface.cpp
@@ -204,8 +204,12 @@ void gl_LoadExtensions()
 	}
 	else if (gl.version < 3.0f)
 	{
-		//if (CheckExtension("GL_NV_GPU_shader4") || CheckExtension("GL_EXT_GPU_shader4")) gl.glslversion = 1.21f;	// for pre-3.0 drivers that support capable hardware. Needed for Apple.
-		//else gl.glslversion = 0;
+		if (CheckExtension("GL_NV_GPU_shader4") || CheckExtension("GL_EXT_GPU_shader4")) gl.glslversion = 1.21f;	// for pre-3.0 drivers that support capable hardware. Needed for Apple.
+		else
+		{
+			gl.buffermethod = BM_CLIENTARRAY;
+			gl.glslversion = 0;
+		}
 
 		if (!CheckExtension("GL_EXT_packed_float")) gl.flags |= RFL_NO_RGBA16F;
 		if (!CheckExtension("GL_EXT_packed_depth_stencil")) gl.flags |= RFL_NO_DEPTHSTENCIL;