diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index 15aa56da9..d7f46e07e 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -69,7 +69,7 @@ TArray<VSMatrix> gl_MatrixStack;
 void FRenderState::Reset()
 {
 	mTextureEnabled = true;
-	mBrightmapEnabled = mFogEnabled = mGlowEnabled = false;
+	mSplitEnabled = mBrightmapEnabled = mFogEnabled = mGlowEnabled = false;
 	mColorMask[0] = mColorMask[1] = mColorMask[2] = mColorMask[3] = true;
 	currentColorMask[0] = currentColorMask[1] = currentColorMask[2] = currentColorMask[3] = true;
 	mFogColor.d = -1;
@@ -104,6 +104,7 @@ void FRenderState::Reset()
 
 bool FRenderState::ApplyShader()
 {
+	static const float nulvec[] = { 0.f, 0.f, 0.f, 0.f };
 	if (mSpecialEffect > EFF_NONE)
 	{
 		activeShader = GLRenderer->mShaderManager->BindEffect(mSpecialEffect);
@@ -157,7 +158,6 @@ bool FRenderState::ApplyShader()
 	else if (activeShader->currentglowstate)
 	{
 		// if glowing is on, disable it.
-		static const float nulvec[] = { 0.f, 0.f, 0.f, 0.f };
 		activeShader->muGlowTopColor.Set(nulvec);
 		activeShader->muGlowBottomColor.Set(nulvec);
 		activeShader->muGlowTopPlane.Set(nulvec);
@@ -165,6 +165,18 @@ bool FRenderState::ApplyShader()
 		activeShader->currentglowstate = 0;
 	}
 
+	if (mSplitEnabled)
+	{
+		activeShader->muSplitTopPlane.Set(mSplitTopPlane.vec);
+		activeShader->muSplitBottomPlane.Set(mSplitBottomPlane.vec);
+		activeShader->currentsplitstate = 1;
+	}
+	else
+	{
+		activeShader->muSplitTopPlane.Set(nulvec);
+		activeShader->muSplitBottomPlane.Set(nulvec);
+	}
+
 	if (mColormapState != activeShader->currentfixedcolormap)
 	{
 		float r, g, b;
diff --git a/src/gl/renderer/gl_renderstate.h b/src/gl/renderer/gl_renderstate.h
index aa24072c2..d46bb4996 100644
--- a/src/gl/renderer/gl_renderstate.h
+++ b/src/gl/renderer/gl_renderstate.h
@@ -46,6 +46,7 @@ class FRenderState
 	bool mTextureEnabled;
 	bool mFogEnabled;
 	bool mGlowEnabled;
+	bool mSplitEnabled;
 	bool mBrightmapEnabled;
 	bool mColorMask[4];
 	bool currentColorMask[4];
@@ -72,6 +73,7 @@ class FRenderState
 	FStateVec4 mCameraPos;
 	FStateVec4 mGlowTop, mGlowBottom;
 	FStateVec4 mGlowTopPlane, mGlowBottomPlane;
+	FStateVec4 mSplitTopPlane, mSplitBottomPlane;
 	PalEntry mFogColor;
 	PalEntry mObjectColor;
 	FStateVec4 mDynColor;
@@ -229,6 +231,11 @@ public:
 		mGlowEnabled = on;
 	}
 
+	void EnableSplit(bool on)
+	{
+		mSplitEnabled = on;
+	}
+
 	void SetLightIndex(int n)
 	{
 		mLightIndex = n;
@@ -272,6 +279,12 @@ public:
 		mGlowBottomPlane.Set(FIXED2FLOAT(bottom.a), FIXED2FLOAT(bottom.b), FIXED2FLOAT(bottom.ic), FIXED2FLOAT(bottom.d));
 	}
 
+	void SetSplitPlanes(const secplane_t &top, const secplane_t &bottom)
+	{
+		mSplitTopPlane.Set(FIXED2FLOAT(top.a), FIXED2FLOAT(top.b), FIXED2FLOAT(top.ic), FIXED2FLOAT(top.d));
+		mSplitBottomPlane.Set(FIXED2FLOAT(bottom.a), FIXED2FLOAT(bottom.b), FIXED2FLOAT(bottom.ic), FIXED2FLOAT(bottom.d));
+	}
+
 	void SetDynLight(float r, float g, float b)
 	{
 		mDynColor.Set(r, g, b, 0);
diff --git a/src/gl/scene/gl_wall.h b/src/gl/scene/gl_wall.h
index 5b27d9435..6dc694585 100644
--- a/src/gl/scene/gl_wall.h
+++ b/src/gl/scene/gl_wall.h
@@ -150,6 +150,8 @@ public:
 	FTextureID topflat,bottomflat;
 	secplane_t topplane, bottomplane;	// we need to save these to pass them to the shader for calculating glows.
 
+	secplane_t *toplight, *bottomlight;	// These refer to the planes within the lightlist_t entries.
+
 	// these are not the same as ytop and ybottom!!!
 	float zceil[2];
 	float zfloor[2];
diff --git a/src/gl/shaders/gl_shader.cpp b/src/gl/shaders/gl_shader.cpp
index 2955cf7c8..aa8dfac2b 100644
--- a/src/gl/shaders/gl_shader.cpp
+++ b/src/gl/shaders/gl_shader.cpp
@@ -216,6 +216,8 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 	muGlowTopColor.Init(hShader, "uGlowTopColor");
 	muGlowBottomPlane.Init(hShader, "uGlowBottomPlane");
 	muGlowTopPlane.Init(hShader, "uGlowTopPlane");
+	muSplitBottomPlane.Init(hShader, "uSplitBottomPlane");
+	muSplitTopPlane.Init(hShader, "uSplitTopPlane");
 	muFixedColormap.Init(hShader, "uFixedColormap");
 	muInterpolationFactor.Init(hShader, "uInterpolationFactor");
 	muClipHeightTop.Init(hShader, "uClipHeightTop");
diff --git a/src/gl/shaders/gl_shader.h b/src/gl/shaders/gl_shader.h
index c5baceceb..cf6480d9b 100644
--- a/src/gl/shaders/gl_shader.h
+++ b/src/gl/shaders/gl_shader.h
@@ -218,6 +218,8 @@ class FShader
 	FUniform4f muGlowTopColor;
 	FUniform4f muGlowBottomPlane;
 	FUniform4f muGlowTopPlane;
+	FUniform4f muSplitBottomPlane;
+	FUniform4f muSplitTopPlane;
 	FBufferedUniform1f muInterpolationFactor;
 	FBufferedUniform1f muClipHeightTop;
 	FBufferedUniform1f muClipHeightBottom;
@@ -233,6 +235,7 @@ public:
 	int fakevb_index;
 private:
 	int currentglowstate;
+	int currentsplitstate;
 	int currentfixedcolormap;
 	bool currentTextureMatrixState;
 	bool currentModelMatrixState;
@@ -243,6 +246,7 @@ public:
 	{
 		hShader = hVertProg = hFragProg = 0;
 		currentglowstate = 0;
+		currentsplitstate = 0;
 		currentfixedcolormap = 0;
 		currentTextureMatrixState = true;	// by setting the matrix state to 'true' it is guaranteed to be set the first time the render state gets applied.
 		currentModelMatrixState = true;
diff --git a/src/gl/system/gl_interface.cpp b/src/gl/system/gl_interface.cpp
index 2e7d0f1e0..3fd718ff7 100644
--- a/src/gl/system/gl_interface.cpp
+++ b/src/gl/system/gl_interface.cpp
@@ -174,7 +174,7 @@ void gl_LoadExtensions()
 void gl_PrintStartupLog()
 {
 	int v = 0;
-	glGetIntegerv(GL_CONTEXT_PROFILE_MASK, &v);
+	if (gl.version >= 3.2) glGetIntegerv(GL_CONTEXT_PROFILE_MASK, &v);
 
 	Printf ("GL_VENDOR: %s\n", glGetString(GL_VENDOR));
 	Printf ("GL_RENDERER: %s\n", glGetString(GL_RENDERER));
diff --git a/wadsrc/static/shaders/glsl/main.vp b/wadsrc/static/shaders/glsl/main.vp
index 827644eea..1c6aebe47 100644
--- a/wadsrc/static/shaders/glsl/main.vp
+++ b/wadsrc/static/shaders/glsl/main.vp
@@ -29,6 +29,12 @@ void main()
 
 		glowdist.x = -((uGlowTopPlane.w + uGlowTopPlane.x * worldcoord.x + uGlowTopPlane.y * worldcoord.z) * uGlowTopPlane.z) - worldcoord.y;
 		glowdist.y = worldcoord.y + ((uGlowBottomPlane.w + uGlowBottomPlane.x * worldcoord.x + uGlowBottomPlane.y * worldcoord.z) * uGlowBottomPlane.z);
+
+		if (uSplitBottomPlane.z != 0)
+		{
+			gl_ClipDistance[3] = -((uSplitTopPlane.w + uSplitTopPlane.x * worldcoord.x + uSplitTopPlane.y * worldcoord.z) * uSplitTopPlane.z) - worldcoord.y;
+			gl_ClipDistance[4] = worldcoord.y + ((uSplitBottomPlane.w + uSplitBottomPlane.x * worldcoord.x + uSplitBottomPlane.y * worldcoord.z) * uSplitBottomPlane.z);
+		}
 	#endif
 	
 	#ifdef SPHEREMAP
@@ -56,4 +62,5 @@ void main()
 	
 	gl_ClipDistance[1] = worldcoord.y - uClipSplit.x;
 	gl_ClipDistance[2] = uClipSplit.y - worldcoord.y;
+	
 }