diff --git a/src/gl/data/gl_matrix.cpp b/src/gl/data/gl_matrix.cpp
index 35683dbb8..a16dc770f 100644
--- a/src/gl/data/gl_matrix.cpp
+++ b/src/gl/data/gl_matrix.cpp
@@ -10,6 +10,7 @@ This is a simplified version of VSMatrix that has been adjusted for GZDoom's nee
 
 ----------------------------------------------------*/
 
+#include <algorithm>
 #include "gl/system/gl_system.h"
 #include <math.h>
 #include <stdlib.h>
@@ -139,14 +140,9 @@ VSMatrix::translate(FLOATTYPE x, FLOATTYPE y, FLOATTYPE z)
 void 
 VSMatrix::scale(FLOATTYPE x, FLOATTYPE y, FLOATTYPE z) 
 {
-	FLOATTYPE mat[16];
-
-	setIdentityMatrix(mat,4);
-	mat[0] = x;
-	mat[5] = y;
-	mat[10] = z;
-
-	multMatrix(mat);
+	mMatrix[0] *= x;   mMatrix[1] *= x;   mMatrix[2] *= x;   mMatrix[3] *= x;
+	mMatrix[4] *= y;   mMatrix[5] *= y;   mMatrix[6] *= y;   mMatrix[7] *= y;
+	mMatrix[8] *= z;   mMatrix[9] *= z;   mMatrix[10] *= z;   mMatrix[11] *= z;
 }
 
 
diff --git a/src/gl/data/gl_matrix.h b/src/gl/data/gl_matrix.h
index de4b400da..3ec1f5ff4 100644
--- a/src/gl/data/gl_matrix.h
+++ b/src/gl/data/gl_matrix.h
@@ -48,6 +48,7 @@ class VSMatrix {
 #ifdef USE_DOUBLE
 		void multMatrix(const float *aMatrix);
 #endif
+		void multVector(FLOATTYPE *aVector);
 		void multMatrix(const FLOATTYPE *aMatrix);
 		void multMatrix(const VSMatrix &aMatrix)
 		{
@@ -92,7 +93,9 @@ class VSMatrix {
 		{
 			computeNormalMatrix(aMatrix.mMatrix);
 		}
-		
+		bool inverseMatrix(VSMatrix &result);
+		void transpose();
+
 	protected:
 		static void crossProduct(const FLOATTYPE *a, const FLOATTYPE *b, FLOATTYPE *res);
 		static FLOATTYPE dotProduct(const FLOATTYPE *a, const FLOATTYPE * b);
diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index d1e30c560..fdb0e3cc5 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -86,8 +86,8 @@ void FRenderState::Reset()
 	mColormapState = CM_DEFAULT;
 	mLightParms[3] = -1.f;
 	mSpecialEffect = EFF_NONE;
-	mClipHeightTop = 65536.f;
-	mClipHeightBottom = -65536.f;
+	mClipHeight = 0.f;
+	mClipHeightDirection = 0.f;
 	ClearClipSplit();
 
 	stSrcBlend = stDstBlend = -1;
@@ -140,8 +140,8 @@ bool FRenderState::ApplyShader()
 	activeShader->muObjectColor.Set(mObjectColor);
 	activeShader->muDynLightColor.Set(mDynColor.vec);
 	activeShader->muInterpolationFactor.Set(mInterpolationFactor);
-	activeShader->muClipHeightTop.Set(mClipHeightTop);
-	activeShader->muClipHeightBottom.Set(mClipHeightBottom);
+	activeShader->muClipHeight.Set(mClipHeight);
+	activeShader->muClipHeightDirection.Set(mClipHeightDirection);
 	activeShader->muTimer.Set(gl_frameMS * mShaderTimer / 1000.f);
 	activeShader->muAlphaThreshold.Set(mAlphaThreshold);
 	activeShader->muLightIndex.Set(mLightIndex);	// will always be -1 for now
@@ -324,4 +324,27 @@ void FRenderState::ApplyLightIndex(int index)
 		}
 		activeShader->muLightIndex.Set(index);
 	}
-}
\ No newline at end of file
+}
+
+void FRenderState::SetClipHeight(float height, float direction)
+{
+	mClipHeight = height;
+	mClipHeightDirection = direction;
+	if (direction != 0.f)
+	{
+		if (gl.glslversion >= 1.3f) glEnable(GL_CLIP_DISTANCE0);
+		else
+		{
+			// This does not work. Need someone who understands how glClipPlane works...
+			//glEnable(GL_CLIP_PLANE0);
+			// Plane mirrors never are slopes.
+			//double d[4] = { 0, direction, 0, -direction * height };
+			//glClipPlane(GL_CLIP_PLANE0, d);
+		}
+	}
+	else
+	{
+		if (gl.glslversion >= 1.3f) glDisable(GL_CLIP_DISTANCE0);
+		//else glDisable(GL_CLIP_PLANE0);
+	}
+}
diff --git a/src/gl/renderer/gl_renderstate.h b/src/gl/renderer/gl_renderstate.h
index e61ab004d..ca240c398 100644
--- a/src/gl/renderer/gl_renderstate.h
+++ b/src/gl/renderer/gl_renderstate.h
@@ -63,7 +63,7 @@ class FRenderState
 	bool mModelMatrixEnabled;
 	bool mTextureMatrixEnabled;
 	float mInterpolationFactor;
-	float mClipHeightTop, mClipHeightBottom;
+	float mClipHeight, mClipHeightDirection;
 	float mShaderTimer;
 	bool mLastDepthClamp;
 
@@ -135,25 +135,17 @@ public:
 		mCurrentVertexBuffer = NULL;
 	}
 
-	void SetClipHeightTop(float clip)
+	float GetClipHeight()
 	{
-		mClipHeightTop = clip;
+		return mClipHeight;
 	}
 
-	float GetClipHeightTop()
+	float GetClipHeightDirection()
 	{
-		return mClipHeightTop;
+		return mClipHeightDirection;
 	}
 
-	void SetClipHeightBottom(float clip)
-	{
-		mClipHeightBottom = clip;
-	}
-
-	float GetClipHeightBottom()
-	{
-		return mClipHeightBottom;
-	}
+	void SetClipHeight(float height, float direction);
 
 	void SetColor(float r, float g, float b, float a = 1.f, int desat = 0)
 	{
diff --git a/src/gl/scene/gl_flats.cpp b/src/gl/scene/gl_flats.cpp
index c90e9541b..7406bb20e 100644
--- a/src/gl/scene/gl_flats.cpp
+++ b/src/gl/scene/gl_flats.cpp
@@ -438,7 +438,7 @@ void GLFlat::Draw(int pass, bool trans)	// trans only has meaning for GLPASS_LIG
 		{
 			gl_RenderState.SetMaterial(gltexture, CLAMP_NONE, 0, -1, false);
 			gl_SetPlaneTextureRotation(&plane, gltexture);
-			DrawSubsectors(pass, true, true);
+			DrawSubsectors(pass, gl.lightmethod != LM_SOFTWARE, true);
 			gl_RenderState.EnableTextureMatrix(false);
 		}
 		if (renderstyle==STYLE_Add) gl_RenderState.BlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
diff --git a/src/gl/scene/gl_portal.cpp b/src/gl/scene/gl_portal.cpp
index 6c2a05592..93f25f28e 100644
--- a/src/gl/scene/gl_portal.cpp
+++ b/src/gl/scene/gl_portal.cpp
@@ -300,11 +300,9 @@ bool GLPortal::Start(bool usestencil, bool doquery)
 			glDisable(GL_DEPTH_TEST);
 		}
 	}
-	planestack.Push(gl_RenderState.GetClipHeightTop());
-	planestack.Push(gl_RenderState.GetClipHeightBottom());
-	glDisable(GL_CLIP_DISTANCE0);
-	gl_RenderState.SetClipHeightBottom(-65536.f);
-	gl_RenderState.SetClipHeightTop(65536.f);
+	planestack.Push(gl_RenderState.GetClipHeight());
+	planestack.Push(gl_RenderState.GetClipHeightDirection());
+	gl_RenderState.SetClipHeight(0., 0.);
 
 	// save viewpoint
 	savedViewPos = ViewPos;
@@ -363,13 +361,10 @@ void GLPortal::End(bool usestencil)
 	PortalAll.Clock();
 	GLRenderer->mCurrentPortal = NextPortal;
 
-	float f;
+	float f, d;
+	planestack.Pop(d);
 	planestack.Pop(f);
-	gl_RenderState.SetClipHeightBottom(f);
-	if (f > -65535.f) glEnable(GL_CLIP_DISTANCE0);
-	planestack.Pop(f);
-	gl_RenderState.SetClipHeightTop(f);
-	if (f < 65535.f) glEnable(GL_CLIP_DISTANCE0);
+	gl_RenderState.SetClipHeight(f, d);
 
 	if (usestencil)
 	{
@@ -804,22 +799,9 @@ void GLPlaneMirrorPortal::DrawContents()
 	GLRenderer->SetupView(ViewPos.X, ViewPos.Y, ViewPos.Z, ViewAngle, !!(MirrorFlag&1), !!(PlaneMirrorFlag&1));
 	ClearClipper();
 
-	if (PlaneMirrorMode < 0)
-	{
-		gl_RenderState.SetClipHeightTop(planez);	// ceiling mirror: clip everything with a z lower than the portal's ceiling
-		gl_RenderState.SetClipHeightBottom(-65536.f);
-	}
-	else
-	{
-		gl_RenderState.SetClipHeightBottom(planez);	// floor mirror: clip everything with a z higher than the portal's floor
-		gl_RenderState.SetClipHeightTop(65536.f);
-	}
-
-	glEnable(GL_CLIP_DISTANCE0);
+	gl_RenderState.SetClipHeight(planez, PlaneMirrorMode < 0? -1.f : 1.f);
 	GLRenderer->DrawScene();
-	glDisable(GL_CLIP_DISTANCE0);
-	gl_RenderState.SetClipHeightBottom(-65536.f);
-	gl_RenderState.SetClipHeightTop(65536.f);
+	gl_RenderState.SetClipHeight(0.f, 0.f);
 	PlaneMirrorFlag--;
 	PlaneMirrorMode=old_pm;
 }
diff --git a/src/gl/shaders/gl_shader.cpp b/src/gl/shaders/gl_shader.cpp
index af6accdb5..a86c57101 100644
--- a/src/gl/shaders/gl_shader.cpp
+++ b/src/gl/shaders/gl_shader.cpp
@@ -280,8 +280,8 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 	muSplitTopPlane.Init(hShader, "uSplitTopPlane");
 	muFixedColormap.Init(hShader, "uFixedColormap");
 	muInterpolationFactor.Init(hShader, "uInterpolationFactor");
-	muClipHeightTop.Init(hShader, "uClipHeightTop");
-	muClipHeightBottom.Init(hShader, "uClipHeightBottom");
+	muClipHeight.Init(hShader, "uClipHeight");
+	muClipHeightDirection.Init(hShader, "uClipHeightDirection");
 	muAlphaThreshold.Init(hShader, "uAlphaThreshold");
 	muTimer.Init(hShader, "timer");
 
diff --git a/src/gl/shaders/gl_shader.h b/src/gl/shaders/gl_shader.h
index cf6480d9b..a7f7e4277 100644
--- a/src/gl/shaders/gl_shader.h
+++ b/src/gl/shaders/gl_shader.h
@@ -221,8 +221,8 @@ class FShader
 	FUniform4f muSplitBottomPlane;
 	FUniform4f muSplitTopPlane;
 	FBufferedUniform1f muInterpolationFactor;
-	FBufferedUniform1f muClipHeightTop;
-	FBufferedUniform1f muClipHeightBottom;
+	FBufferedUniform1f muClipHeight;
+	FBufferedUniform1f muClipHeightDirection;
 	FBufferedUniform1f muAlphaThreshold;
 	FBufferedUniform1f muTimer;
 	
diff --git a/wadsrc/static/glstuff/gllight.png b/wadsrc/static/glstuff/gllight.png
new file mode 100644
index 000000000..a3a296b9f
Binary files /dev/null and b/wadsrc/static/glstuff/gllight.png differ