diff --git a/src/gl/renderer/gl_renderer.cpp b/src/gl/renderer/gl_renderer.cpp
index 9654f8998..da6a8e54c 100644
--- a/src/gl/renderer/gl_renderer.cpp
+++ b/src/gl/renderer/gl_renderer.cpp
@@ -375,7 +375,7 @@ void FGLRenderer::DrawTexture(FTexture *img, DCanvas::DrawParms &parms)
 	{
 		color = PalEntry(light, light, light);
 	}
-	color.a = Scale(parms.alpha, 255, FRACUNIT);
+	color.a = (BYTE)(parms.Alpha * 255);
 
 	// scissor test doesn't use the current viewport for the coordinates, so use real screen coordinates
 	int btm = (SCREENHEIGHT - screen->GetHeight()) / 2;
diff --git a/src/gl/scene/gl_decal.cpp b/src/gl/scene/gl_decal.cpp
index de175fffd..0bda67191 100644
--- a/src/gl/scene/gl_decal.cpp
+++ b/src/gl/scene/gl_decal.cpp
@@ -71,7 +71,7 @@ void GLWall::DrawDecal(DBaseDecal *decal)
 	line_t * line=seg->linedef;
 	side_t * side=seg->sidedef;
 	int i;
-	fixed_t zpos;
+	float zpos;
 	int light;
 	int rel;
 	float a;
@@ -129,33 +129,33 @@ void GLWall::DrawDecal(DBaseDecal *decal)
 		if (type!=RENDERWALL_TOP) return;
 		if (line->flags & ML_DONTPEGTOP)
 		{
-			zpos = decal->Z + frontsector->GetPlaneTexZ(sector_t::ceiling);
+			zpos = decal->Z + frontsector->GetPlaneTexZF(sector_t::ceiling);
 		}
 		else
 		{
-			zpos = decal->Z + seg->backsector->GetPlaneTexZ(sector_t::ceiling);
+			zpos = decal->Z + seg->backsector->GetPlaneTexZF(sector_t::ceiling);
 		}
 		break;
 	case RF_RELLOWER:
 		if (type!=RENDERWALL_BOTTOM) return;
 		if (line->flags & ML_DONTPEGBOTTOM)
 		{
-			zpos = decal->Z + frontsector->GetPlaneTexZ(sector_t::ceiling);
+			zpos = decal->Z + frontsector->GetPlaneTexZF(sector_t::ceiling);
 		}
 		else
 		{
-			zpos = decal->Z + seg->backsector->GetPlaneTexZ(sector_t::floor);
+			zpos = decal->Z + seg->backsector->GetPlaneTexZF(sector_t::floor);
 		}
 		break;
 	case RF_RELMID:
 		if (type==RENDERWALL_TOP || type==RENDERWALL_BOTTOM) return;
 		if (line->flags & ML_DONTPEGBOTTOM)
 		{
-			zpos = decal->Z + frontsector->GetPlaneTexZ(sector_t::floor);
+			zpos = decal->Z + frontsector->GetPlaneTexZF(sector_t::floor);
 		}
 		else
 		{
-			zpos = decal->Z + frontsector->GetPlaneTexZ(sector_t::ceiling);
+			zpos = decal->Z + frontsector->GetPlaneTexZF(sector_t::ceiling);
 		}
 	}
 	
@@ -179,20 +179,20 @@ void GLWall::DrawDecal(DBaseDecal *decal)
 	
 	
 	
-	a = FIXED2FLOAT(decal->Alpha);
+	a = decal->Alpha;
 	
 	// now clip the decal to the actual polygon
-	float decalwidth = tex->TextureWidth()  * FIXED2FLOAT(decal->ScaleX);
-	float decalheight= tex->TextureHeight() * FIXED2FLOAT(decal->ScaleY);
-	float decallefto = tex->GetLeftOffset() * FIXED2FLOAT(decal->ScaleX);
-	float decaltopo  = tex->GetTopOffset()  * FIXED2FLOAT(decal->ScaleY);
+	float decalwidth = tex->TextureWidth()  * decal->ScaleX;
+	float decalheight= tex->TextureHeight() * decal->ScaleY;
+	float decallefto = tex->GetLeftOffset() * decal->ScaleX;
+	float decaltopo  = tex->GetTopOffset()  * decal->ScaleY;
 
 	
 	float leftedge = glseg.fracleft * side->TexelLength;
 	float linelength = glseg.fracright * side->TexelLength - leftedge;
 
 	// texel index of the decal's left edge
-	float decalpixpos = (float)side->TexelLength * decal->LeftDistance / (1<<30) - (flipx? decalwidth-decallefto : decallefto) - leftedge;
+	float decalpixpos = (float)side->TexelLength * decal->LeftDistance - (flipx? decalwidth-decallefto : decallefto) - leftedge;
 
 	float left,right;
 	float lefttex,righttex;
@@ -232,14 +232,14 @@ void GLWall::DrawDecal(DBaseDecal *decal)
 	dv[3].x=dv[2].x=glseg.x1+vx*right;
 	dv[3].y=dv[2].y=glseg.y1+vy*right;
 		
-	zpos+= FRACUNIT*(flipy? decalheight-decaltopo : decaltopo);
+	zpos+= (flipy? decalheight-decaltopo : decaltopo);
 
-	dv[1].z=dv[2].z = FIXED2FLOAT(zpos);
+	dv[1].z=dv[2].z = zpos;
 	dv[0].z=dv[3].z = dv[1].z - decalheight;
 	dv[1].v=dv[2].v = tex->GetVT();
 
-	dv[1].u=dv[0].u = tex->GetU(lefttex / FIXED2FLOAT(decal->ScaleX));
-	dv[3].u=dv[2].u = tex->GetU(righttex / FIXED2FLOAT(decal->ScaleX));
+	dv[1].u=dv[0].u = tex->GetU(lefttex / decal->ScaleX);
+	dv[3].u=dv[2].u = tex->GetU(righttex / decal->ScaleX);
 	dv[0].v=dv[3].v = tex->GetVB();
 
 
@@ -297,7 +297,7 @@ void GLWall::DrawDecal(DBaseDecal *decal)
 	if (gl_lights && GLRenderer->mLightCount && !gl_fixedcolormap && gl_light_sprites)
 	{
 		// Note: This should be replaced with proper shader based lighting.
-		fixed_t x, y;
+		double x, y;
 		decal->GetXY(seg->sidedef, x, y);
 		gl_SetDynSpriteLight(NULL, x, y, zpos, sub);
 	}
diff --git a/src/gl/scene/gl_spritelight.cpp b/src/gl/scene/gl_spritelight.cpp
index 7cfb0e908..2afc67524 100644
--- a/src/gl/scene/gl_spritelight.cpp
+++ b/src/gl/scene/gl_spritelight.cpp
@@ -63,7 +63,7 @@
 //
 //==========================================================================
 
-void gl_SetDynSpriteLight(AActor *self, fixed_t x, fixed_t y, fixed_t z, subsector_t * subsec)
+void gl_SetDynSpriteLight(AActor *self, float x, float y, float z, subsector_t * subsec)
 {
 	ADynamicLight *light;
 	float frac, lr, lg, lb;
@@ -80,7 +80,28 @@ void gl_SetDynSpriteLight(AActor *self, fixed_t x, fixed_t y, fixed_t z, subsect
 			if (!(light->flags2&MF2_DORMANT) &&
 				(!(light->flags4&MF4_DONTLIGHTSELF) || light->target != self))
 			{
-				float dist = FVector3(FIXED2FLOAT(x - light->_f_X()), FIXED2FLOAT(y - light->_f_Y()), FIXED2FLOAT(z - light->_f_Z())).Length();
+				float dist;
+
+				// This is a performance critical section of code where we cannot afford to let the compiler decide whether to inline the function or not.
+				// This will do the calculations explicitly rather than calling one of AActor's utility functions.
+				if (Displacements.size > 0)
+				{
+					int fromgroup = light->Sector->PortalGroup;
+					int togroup = subsec->sector->PortalGroup;
+					if (fromgroup == togroup || fromgroup == 0 || togroup == 0) goto direct;	
+
+					fixedvec2 offset = Displacements.getOffset(fromgroup, togroup);
+					dist = FVector3(x - light->X() - FIXED2FLOAT(offset.x), y - light->Y() - FIXED2FLOAT(offset.y), z - light->Z()).LengthSquared();
+				}
+				else
+				{
+				direct:
+					dist = FVector3(x - light->X(), y - light->Y(), z - light->Z()).LengthSquared();
+				}
+				// This is to avoid calling the software-implemented sqrt function which gets used by FVector3::Length().
+				// With fast math on in this module this call will be mapped to a machine instruction on most platforms.
+				dist = sqrtf(dist);
+
 				radius = light->GetRadius() * gl_lights_size;
 
 				if (dist < radius)
@@ -117,10 +138,10 @@ void gl_SetDynSpriteLight(AActor *thing, particle_t *particle)
 {
 	if (thing != NULL)
 	{
-		gl_SetDynSpriteLight(thing, thing->_f_X(), thing->_f_Y(), thing->_f_Z() + (thing->_f_height() >> 1), thing->subsector);
+		gl_SetDynSpriteLight(thing, thing->X(), thing->Y(), thing->Center(), thing->subsector);
 	}
 	else if (particle != NULL)
 	{
-		gl_SetDynSpriteLight(NULL, particle->x, particle->y, particle->z, particle->subsector);
+		gl_SetDynSpriteLight(NULL, FIXED2FLOAT(particle->x), FIXED2FLOAT(particle->y), FIXED2FLOAT(particle->z), particle->subsector);
 	}
 }
diff --git a/src/gl/scene/gl_wall.h b/src/gl/scene/gl_wall.h
index ce03267a3..0069fe863 100644
--- a/src/gl/scene/gl_wall.h
+++ b/src/gl/scene/gl_wall.h
@@ -363,7 +363,7 @@ inline float Dist2(float x1,float y1,float x2,float y2)
 
 // Light + color
 
-void gl_SetDynSpriteLight(AActor *self, fixed_t x, fixed_t y, fixed_t z, subsector_t *subsec);
+void gl_SetDynSpriteLight(AActor *self, float x, float y, float z, subsector_t *subsec);
 void gl_SetDynSpriteLight(AActor *actor, particle_t *particle);
 
 #endif
diff --git a/src/gl/scene/gl_weapon.cpp b/src/gl/scene/gl_weapon.cpp
index c8a9889eb..5fa57db50 100644
--- a/src/gl/scene/gl_weapon.cpp
+++ b/src/gl/scene/gl_weapon.cpp
@@ -300,7 +300,7 @@ void FGLRenderer::DrawPlayerSprites(sector_t * viewsector, bool hudModelStep)
 	visstyle_t vis;
 
 	vis.RenderStyle=playermo->RenderStyle;
-	vis.alpha=playermo->Alpha;
+	vis.Alpha=playermo->Alpha;
 	vis.colormap = NULL;
 	if (playermo->Inventory) 
 	{
@@ -350,7 +350,7 @@ void FGLRenderer::DrawPlayerSprites(sector_t * viewsector, bool hudModelStep)
 	}
 	else if (trans == 0.f)
 	{
-		trans = FIXED2FLOAT(vis.alpha);
+		trans = vis.Alpha;
 	}
 
 	// now draw the different layers of the weapon