- more options for Doom 64 style gradients on walls:

* Colors can npw be defined per sidedef, not only per sector.
* Gradients can be selectively disabled or vertically flipped per wall tier.
* Gradients can be clamped to their respective tier, i.e top and bottom of the tier, not the front sector defines where it starts.

The per-wall colors are implemented for hardware and softpoly renderer only, but not for the classic software renderer, because its code is far too scattered to do this efficiently.

# Conflicts:
#	src/hwrenderer/scene/hw_renderstate.h
#	src/hwrenderer/scene/hw_walls.cpp

# Conflicts:
#	src/gl/scene/gl_walls_draw.cpp

specs/udmf_zdoom.txt

@@ -179,6 +179,27 @@ Note: All <bool> fields default to false unless mentioned otherwise.
       clipmidtex = <bool>;          // Side's mid textures are clipped to floor and ceiling.
       wrapmidtex = <bool>;          // Side's mid textures are wrapped.
       nodecals = <bool>;            // Disables decals on the sidedef.
+	  
+	  nogradient_top = <bool>;	    // disables color gradient on upper tier. (Hardware rendering only.)
+	  flipgradient_top = <bool>;    // flips gradient colors on upper tier. (Hardware rendering only.)
+	  clampgradient_top = <bool>;   // clamps gradient on upper tier to actual bounds (default is the entire front sector height, hardware rendering only.)
+	  useowncolors_top = <bool>;    // Set to 1 to use the colors set in the sidedef. Default is using the colors from the owning sector.
+	  uppercolor_top = <int>;       // Material color of the top of the upper tier.
+	  lowercolor_top = <int>;       // Material color of the bottom of the upper tier. (Hardware rendering only.)
+	  
+	  nogradient_mid = <bool>;	    // disables color gradient on middle tier. (Hardware rendering only.)
+	  flipgradient_mid = <bool>;    // flips gradient colors on middle tier. (Hardware rendering only.)
+	  clampgradient_mid = <bool>;   // clamps gradient on middle tier to actual bounds (default is the entire front sector height, hardware rendering only.)
+	  useowncolors_mid = <bool>;    // Set to 1 to use the colors set in the sidedef. Default is using the colors from the owning sector.
+	  uppercolor_mid = <int>;       // Material color of the top of the middle tier.
+	  lowercolor_mid = <int>;       // Material color of the bottom of the middle tier. (Hardware rendering only.)
+
+	  nogradient_bottom = <bool>;   // disables color gradient on lower tier. (Hardware rendering only.)
+	  flipgradient_bottom = <bool>; // flips gradient colors on lower tier. (Hardware rendering only.)
+	  clampgradient_bottom = <bool>;// clamps gradient on lower tier to actual bounds (default is the entire front sector height, hardware rendering only.)
+	  useowncolors_bottom = <bool>; // Set to 1 to use the colors set in the sidedef. Default is using the colors from the owning sector.
+	  uppercolor_bottom = <int>;    // Material color of the top of the lower tier.
+	  lowercolor_bottom = <int>;    // Material color of the bottom of the lower tier. (Hardware rendering only.)
    }
 
    sector

src/gl/renderer/gl_renderstate.cpp

@@ -68,7 +68,7 @@ static void matrixToGL(const VSMatrix &mat, int loc)
 void FRenderState::Reset()
 {
 	mTextureEnabled = true;
-	mClipLineEnabled = mSplitEnabled = mBrightmapEnabled = mFogEnabled = mGlowEnabled = false;
+	mClipLineEnabled = mSplitEnabled = mGradientEnabled = 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;
@@ -109,6 +109,8 @@ void FRenderState::Reset()
 	mGlowBottom.Set(0.0f, 0.0f, 0.0f, 0.0f);
 	mGlowTopPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
 	mGlowBottomPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mGradientTopPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
+	mGradientBottomPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
 	mSplitTopPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
 	mSplitBottomPlane.Set(0.0f, 0.0f, 0.0f, 0.0f);
 	mClipLine.Set(0.0f, 0.0f, 0.0f, 0.0f);

src/gl/renderer/gl_renderstate.h

@@ -75,6 +75,7 @@ class FRenderState
 	bool mTextureEnabled;
 	bool mFogEnabled;
 	bool mGlowEnabled;
+	bool mGradientEnabled;
 	bool mSplitEnabled;
 	bool mClipLineEnabled;
 	bool mBrightmapEnabled;
@@ -103,6 +104,7 @@ class FRenderState
 	FStateVec4 mCameraPos;
 	FStateVec4 mGlowTop, mGlowBottom;
 	FStateVec4 mGlowTopPlane, mGlowBottomPlane;
+	FStateVec4 mGradientTopPlane, mGradientBottomPlane;
 	FStateVec4 mSplitTopPlane, mSplitBottomPlane;
 	FStateVec4 mClipLine;
 	PalEntry mFogColor;
@@ -285,6 +287,11 @@ public:
 		mGlowEnabled = on;
 	}
 
+	void EnableGradient(bool on)
+	{
+		mGradientEnabled = on;
+	}
+
 	void EnableSplit(bool on)
 	{
 		if (!(gl.flags & RFL_NO_CLIP_PLANES))
@@ -369,6 +376,14 @@ public:
 		mGlowBottomPlane.Set(bn.X, bn.Y, 1. / bn.Z, bottom.fD());
 	}
 
+	void SetGradientPlanes(const secplane_t &top, const secplane_t &bottom)
+	{
+		DVector3 tn = top.Normal();
+		DVector3 bn = bottom.Normal();
+		mGradientTopPlane.Set(tn.X, tn.Y, 1. / tn.Z, top.fD());
+		mGradientBottomPlane.Set(bn.X, bn.Y, 1. / bn.Z, bottom.fD());
+	}
+
 	void SetSplitPlanes(const secplane_t &top, const secplane_t &bottom)
 	{
 		DVector3 tn = top.Normal();

src/gl/scene/gl_walls_draw.cpp

@@ -324,6 +324,20 @@ void GLWall::RenderMirrorSurface()
 //
 //==========================================================================
 
+static const uint8_t renderwalltotier[] =
+{
+	side_t::none,
+	side_t::top,
+	side_t::mid,
+	side_t::mid,
+	side_t::bottom,
+	side_t::none,
+	side_t::none,
+	side_t::mid,
+	side_t::none,
+	side_t::mid,
+};
+
 void GLWall::RenderTextured(int rflags)
 {
 	int tmode = gl_RenderState.GetTextureMode();
@@ -333,8 +347,8 @@ void GLWall::RenderTextured(int rflags)
 	{
 		gl_RenderState.EnableGlow(true);
 		gl_RenderState.SetGlowParams(topglowcolor, bottomglowcolor);
-	}
 		gl_RenderState.SetGlowPlanes(frontsector->ceilingplane, frontsector->floorplane);
+	}
 	gl_RenderState.SetMaterial(gltexture, flags & 3, 0, -1, false);
 
 	if (type == RENDERWALL_M2SNF)
@@ -345,11 +359,44 @@ void GLWall::RenderTextured(int rflags)
 		}
 		mDrawer->SetFog(255, 0, NULL, false);
 	}
-	gl_RenderState.SetObjectColor(seg->frontsector->SpecialColors[sector_t::walltop] | 0xff000000);
+	if (type != RENDERWALL_COLOR)
-	gl_RenderState.SetObjectColor2(seg->frontsector->SpecialColors[sector_t::wallbottom] | 0xff000000);
+	{
+		auto side = seg->sidedef;
+		auto tierndx = renderwalltotier[type];
+		auto &tier = side->textures[tierndx];
+		PalEntry color1 = side->GetSpecialColor(tierndx, side_t::walltop, frontsector);
+		PalEntry color2 = side->GetSpecialColor(tierndx, side_t::wallbottom, frontsector);
+		gl_RenderState.SetObjectColor(color1);
+		gl_RenderState.SetObjectColor2(color2);
+		if (color1 != color2)
+		{
+			// Do gradient setup only if there actually is a gradient.
+
+			gl_RenderState.EnableGradient(true);
+			if ((tier.flags & side_t::part::ClampGradient) && backsector)
+			{
+				if (tierndx == side_t::top)
+				{
+					gl_RenderState.SetGradientPlanes(frontsector->ceilingplane, backsector->ceilingplane);
+				}
+				else if (tierndx == side_t::mid)
+				{
+					gl_RenderState.SetGradientPlanes(backsector->ceilingplane, backsector->floorplane);
+				}
+				else // side_t::bottom:
+				{
+					gl_RenderState.SetGradientPlanes(backsector->floorplane, frontsector->floorplane);
+				}
+			}
+			else
+			{
+				gl_RenderState.SetGradientPlanes(frontsector->ceilingplane, frontsector->floorplane);
+			}
+		}
+	}
 
 	float absalpha = fabsf(alpha);
-	if (lightlist == NULL)
+	if (lightlist == nullptr)
 	{
 		if (type != RENDERWALL_M2SNF) mDrawer->SetFog(lightlevel, rel, &Colormap, RenderStyle == STYLE_Add);
 		mDrawer->SetColor(lightlevel, rel, Colormap, absalpha);
@@ -368,7 +415,7 @@ void GLWall::RenderTextured(int rflags)
 
 			if (low1 < ztop[0] || low2 < ztop[1])
 			{
-				int thisll = (*lightlist)[i].caster != NULL ? gl_ClampLight(*(*lightlist)[i].p_lightlevel) : lightlevel;
+				int thisll = (*lightlist)[i].caster != nullptr ? gl_ClampLight(*(*lightlist)[i].p_lightlevel) : lightlevel;
 				FColormap thiscm;
 				thiscm.FadeColor = Colormap.FadeColor;
 				thiscm.FogDensity = Colormap.FogDensity;
@@ -387,6 +434,7 @@ void GLWall::RenderTextured(int rflags)
 	gl_RenderState.SetObjectColor2(0);
 	gl_RenderState.SetTextureMode(tmode);
 	gl_RenderState.EnableGlow(false);
+	gl_RenderState.EnableGradient(false);
 }
 
 //==========================================================================

src/gl/shaders/gl_shader.cpp

@@ -173,6 +173,9 @@ bool FShader::Load(const char * name, const char * vert_prog_lump, const char *
 	i_data += "uniform vec4 uGlowBottomPlane;\n";
 	i_data += "uniform vec4 uGlowBottomColor;\n";
 
+	i_data += "uniform vec4 uGradientTopPlane;\n";
+	i_data += "uniform vec4 uGradientBottomPlane;\n";
+
 	i_data += "uniform vec4 uSplitTopPlane;\n";
 	i_data += "uniform vec4 uSplitBottomPlane;\n";
 
@@ -461,6 +464,8 @@ 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");
+	muGradientBottomPlane.Init(hShader, "uGradientBottomPlane");
+	muGradientTopPlane.Init(hShader, "uGradientTopPlane");
 	muSplitBottomPlane.Init(hShader, "uSplitBottomPlane");
 	muSplitTopPlane.Init(hShader, "uSplitTopPlane");
 	muClipLine.Init(hShader, "uClipLine");

src/gl/shaders/gl_shader.h

@@ -277,6 +277,8 @@ class FShader
 	FUniform4f muGlowTopColor;
 	FUniform4f muGlowBottomPlane;
 	FUniform4f muGlowTopPlane;
+	FUniform4f muGradientBottomPlane;
+	FUniform4f muGradientTopPlane;
 	FUniform4f muSplitBottomPlane;
 	FUniform4f muSplitTopPlane;
 	FUniform4f muClipLine;
@@ -303,6 +305,7 @@ public:
 	int fakevb_index;
 private:
 	int currentglowstate = 0;
+	int currentgradientstate = 0;
 	int currentsplitstate = 0;
 	int currentcliplinestate = 0;
 	int currentfixedcolormap = 0;

src/namedef.h

@@ -630,6 +630,26 @@ xx(hidden)
 xx(blocksight)
 xx(blockhitscan)
 
+xx(nogradient_top)
+xx(flipgradient_top)
+xx(clampgradient_top)
+xx(useowncolors_top)
+xx(uppercolor_top)
+xx(lowercolor_top)
+xx(nogradient_mid)
+xx(flipgradient_mid)
+xx(clampgradient_mid)
+xx(useowncolors_mid)
+xx(uppercolor_mid)
+xx(lowercolor_mid)
+xx(nogradient_bottom)
+xx(flipgradient_bottom)
+xx(clampgradient_bottom)
+xx(useowncolors_bottom)
+xx(uppercolor_bottom)
+xx(lowercolor_bottom)
+
+
 xx(Renderstyle)
 
 xx(ceilingplane_a)

src/p_saveg.cpp

@@ -113,6 +113,9 @@ FSerializer &Serialize(FSerializer &arc, const char *key, side_t::part &part, si
 			("yscale", part.yScale, def->yScale)
 			("texture", part.texture, def->texture)
 			("interpolation", part.interpolation)
+			("flags", part.flags, def->flags)
+			("color1", part.SpecialColors[0], def->SpecialColors[0])
+			("color2", part.SpecialColors[1], def->SpecialColors[1])
 			.EndObject();
 	}
 	return arc;

src/p_sectors.cpp

@@ -879,17 +879,6 @@ DEFINE_ACTION_FUNCTION(_Sector, SetFade)
 //
 //=====================================================================================
 
-void sector_t::SetSpecialColor(int slot, int r, int g, int b)
-{
-	SpecialColors[slot] = PalEntry(255, r, g, b);
-}
-
-void sector_t::SetSpecialColor(int slot, PalEntry rgb)
-{
-	rgb.a = 255;
-	SpecialColors[slot] = rgb;
-}
-
 DEFINE_ACTION_FUNCTION(_Sector, SetSpecialColor)
 {
 	PARAM_SELF_STRUCT_PROLOGUE(sector_t);

src/p_setup.cpp

@@ -4249,9 +4249,21 @@ void P_SetupLevel (const char *lumpname, int position, bool newGame)
 	memcpy(&level.loadlines[0], &level.lines[0], level.lines.Size() * sizeof(level.lines[0]));
 	level.loadsides.Resize(level.sides.Size());
 	memcpy(&level.loadsides[0], &level.sides[0], level.sides.Size() * sizeof(level.sides[0]));
+
+
+	for (auto i : { 29, 30 })
+	{
+		level.lines[i].sidedef[0]->SetSpecialColor(side_t::top, side_t::walltop, PalEntry(255, 255, 0));
+		level.lines[i].sidedef[0]->SetSpecialColor(side_t::top, side_t::wallbottom, PalEntry(0, 255, 255));
+		level.lines[i].sidedef[0]->SetSpecialColor(side_t::bottom, side_t::walltop, PalEntry(255, 0, 0));
+		level.lines[i].sidedef[0]->SetSpecialColor(side_t::bottom, side_t::wallbottom, PalEntry(0, 0, 255));
 	}
+	level.lines[29].sidedef[0]->textures[side_t::top].flags = side_t::part::UseOwnColors;
+	level.lines[30].sidedef[0]->textures[side_t::top].flags = side_t::part::UseOwnColors | side_t::part::ClampGradient;
+	level.lines[29].sidedef[0]->textures[side_t::bottom].flags = side_t::part::UseOwnColors;
+	level.lines[30].sidedef[0]->textures[side_t::bottom].flags = side_t::part::UseOwnColors | side_t::part::ClampGradient;
 
-
+}
 
 //
 // P_Init

src/p_udmf.cpp

@@ -1226,6 +1226,7 @@ public:
 		{
 			FName key = ParseKey();
 			switch(key)
+
 			{
 			case NAME_Offsetx:
 				texOfs[0] = CheckInt(key);
@@ -1337,6 +1338,79 @@ public:
 				Flag(sd->Flags, WALLF_NOAUTODECALS, key);
 				continue;
 
+			case NAME_nogradient_top:
+				Flag(sd->textures[side_t::top].flags, side_t::part::NoGradient, key);
+				break;
+
+			case NAME_flipgradient_top:
+				Flag(sd->textures[side_t::top].flags, side_t::part::FlipGradient, key);
+				break;
+
+			case NAME_clampgradient_top:
+				Flag(sd->textures[side_t::top].flags, side_t::part::ClampGradient, key);
+				break;
+
+			case NAME_useowncolors_top:
+				Flag(sd->textures[side_t::top].flags, side_t::part::UseOwnColors, key);
+				break;
+
+			case NAME_uppercolor_top:
+				sd->SetSpecialColor(side_t::top, 0, CheckInt(key));
+				break;
+
+			case NAME_lowercolor_top:
+				sd->SetSpecialColor(side_t::top, 1, CheckInt(key));
+				break;
+
+			case NAME_nogradient_mid:
+				Flag(sd->textures[side_t::mid].flags, side_t::part::NoGradient, key);
+				break;
+
+			case NAME_flipgradient_mid:
+				Flag(sd->textures[side_t::mid].flags, side_t::part::FlipGradient, key);
+				break;
+
+			case NAME_clampgradient_mid:
+				Flag(sd->textures[side_t::mid].flags, side_t::part::ClampGradient, key);
+				break;
+
+			case NAME_useowncolors_mid:
+				Flag(sd->textures[side_t::mid].flags, side_t::part::UseOwnColors, key);
+				break;
+
+			case NAME_uppercolor_mid:
+				sd->SetSpecialColor(side_t::mid, 0, CheckInt(key));
+				break;
+
+			case NAME_lowercolor_mid:
+				sd->SetSpecialColor(side_t::mid, 1, CheckInt(key));
+				break;
+
+			case NAME_nogradient_bottom:
+				Flag(sd->textures[side_t::bottom].flags, side_t::part::NoGradient, key);
+				break;
+
+			case NAME_flipgradient_bottom:
+				Flag(sd->textures[side_t::bottom].flags, side_t::part::FlipGradient, key);
+				break;
+
+			case NAME_clampgradient_bottom:
+				Flag(sd->textures[side_t::bottom].flags, side_t::part::ClampGradient, key);
+				break;
+
+			case NAME_useowncolors_bottom:
+				Flag(sd->textures[side_t::bottom].flags, side_t::part::UseOwnColors, key);
+				break;
+
+			case NAME_uppercolor_bottom:
+				sd->SetSpecialColor(side_t::bottom, 0, CheckInt(key));
+				break;
+
+			case NAME_lowercolor_bottom:
+				sd->SetSpecialColor(side_t::bottom, 1, CheckInt(key));
+				break;
+
+
 			default:
 				break;
 

src/polyrenderer/scene/poly_wall.cpp

@@ -88,7 +88,6 @@ bool RenderPolyWall::RenderLine(PolyRenderThread *thread, seg_t *line, sector_t
 	wall.Line = line->linedef;
 	wall.Side = line->sidedef;
 	wall.LineSegLine = line->linedef;
-	wall.Colormap = GetColorTable(frontsector->Colormap, frontsector->SpecialColors[sector_t::walltop]);
 	wall.Masked = false;
 	wall.SubsectorDepth = subsectorDepth;
 	wall.StencilValue = stencilValue;
@@ -102,6 +101,7 @@ bool RenderPolyWall::RenderLine(PolyRenderThread *thread, seg_t *line, sector_t
 			wall.TopTexZ = topTexZ;
 			wall.BottomTexZ = bottomTexZ;
 			wall.Wallpart = side_t::mid;
+			wall.Colormap = GetColorTable(frontsector->Colormap, wall.Side->GetSpecialColor(wall.Wallpart, side_t::walltop, frontsector));
 			wall.Texture = GetTexture(wall.Line, wall.Side, side_t::mid);
 			wall.Polyportal = polyportal;
 			wall.Render(thread);
@@ -140,6 +140,7 @@ bool RenderPolyWall::RenderLine(PolyRenderThread *thread, seg_t *line, sector_t
 			wall.TopTexZ = topTexZ;
 			wall.BottomTexZ = MIN(MIN(backceilz1, frontceilz1), MIN(backceilz2, frontceilz2));
 			wall.Wallpart = side_t::top;
+			wall.Colormap = GetColorTable(frontsector->Colormap, wall.Side->GetSpecialColor(wall.Wallpart, side_t::walltop, frontsector));
 			wall.Texture = GetTexture(wall.Line, wall.Side, side_t::top);
 			wall.Render(thread);
 		}
@@ -152,6 +153,7 @@ bool RenderPolyWall::RenderLine(PolyRenderThread *thread, seg_t *line, sector_t
 			wall.UnpeggedCeil1 = topceilz1;
 			wall.UnpeggedCeil2 = topceilz2;
 			wall.Wallpart = side_t::bottom;
+			wall.Colormap = GetColorTable(frontsector->Colormap, wall.Side->GetSpecialColor(wall.Wallpart, side_t::walltop, frontsector));
 			wall.Texture = GetTexture(wall.Line, wall.Side, side_t::bottom);
 			wall.Render(thread);
 		}
@@ -162,6 +164,7 @@ bool RenderPolyWall::RenderLine(PolyRenderThread *thread, seg_t *line, sector_t
 			wall.TopTexZ = MAX(middleceilz1, middleceilz2);
 			wall.BottomTexZ = MIN(middlefloorz1, middlefloorz2);
 			wall.Wallpart = side_t::mid;
+			wall.Colormap = GetColorTable(frontsector->Colormap, wall.Side->GetSpecialColor(wall.Wallpart, side_t::walltop, frontsector));
 			wall.Texture = GetTexture(wall.Line, wall.Side, side_t::mid);
 			wall.Masked = true;
 			wall.Additive = !!(wall.Line->flags & ML_ADDTRANS);
@@ -212,7 +215,6 @@ void RenderPolyWall::Render3DFloorLine(PolyRenderThread *thread, seg_t *line, se
 	wall.LineSegLine = line->linedef;
 	wall.Line = fakeFloor->master;
 	wall.Side = fakeFloor->master->sidedef[0];
-	wall.Colormap = GetColorTable(frontsector->Colormap, frontsector->SpecialColors[sector_t::walltop]);
 	wall.SectorLightLevel = frontsector->lightlevel;
 	wall.Additive = !!(fakeFloor->flags & FF_ADDITIVETRANS);
 	if (!wall.Additive && fakeFloor->alpha == 255)
@@ -231,6 +233,7 @@ void RenderPolyWall::Render3DFloorLine(PolyRenderThread *thread, seg_t *line, se
 	wall.TopTexZ = topTexZ;
 	wall.BottomTexZ = bottomTexZ;
 	wall.Wallpart = side_t::mid;
+	wall.Colormap = GetColorTable(frontsector->Colormap, wall.Side->GetSpecialColor(wall.Wallpart, side_t::walltop, frontsector));
 	if (fakeFloor->flags & FF_UPPERTEXTURE)
 		wall.Texture = GetTexture(line->linedef, line->sidedef, side_t::top);
 	else if (fakeFloor->flags & FF_LOWERTEXTURE)

src/r_defs.h

@@ -325,7 +325,7 @@ public:
 		return !normal.XY().isZero();
 	}
 
-	DVector3 Normal() const
+	const DVector3 &Normal() const
 	{
 		return normal;
 	}
@@ -645,8 +645,6 @@ public:
 	void SetColor(int r, int g, int b, int desat);
 	void SetFade(int r, int g, int b);
 	void SetFogDensity(int dens);
-	void SetSpecialColor(int num, int r, int g, int b);
-	void SetSpecialColor(int num, PalEntry rgb);
 	void ClosestPoint(const DVector2 &pos, DVector2 &out) const;
 	int GetFloorLight () const;
 	int GetCeilingLight () const;
@@ -914,6 +912,17 @@ public:
 		Flags &= ~SECF_SPECIALFLAGS;
 	}
 
+	void SetSpecialColor(int slot, int r, int g, int b)
+	{
+		SpecialColors[slot] = PalEntry(255, r, g, b);
+	}
+
+	void SetSpecialColor(int slot, PalEntry rgb)
+	{
+		rgb.a = 255;
+		SpecialColors[slot] = rgb;
+	}
+
 	inline bool PortalBlocksView(int plane);
 	inline bool PortalBlocksSight(int plane);
 	inline bool PortalBlocksMovement(int plane);
@@ -1149,16 +1158,31 @@ struct side_t
 	{
 		top=0,
 		mid=1,
-		bottom=2
+		bottom=2,
+		none = 1,	// this is just for clarification in a mapping table
+	};
+	enum EColorSlot
+	{
+		walltop = 0,
+		wallbottom = 1,
 	};
 	struct part
 	{
+		enum EPartFlags
+		{
+			NoGradient = 1,
+			FlipGradient = 2,
+			ClampGradient = 4,
+			UseOwnColors = 8,
+		};
 		double xOffset;
 		double yOffset;
 		double xScale;
 		double yScale;
 		TObjPtr<DInterpolation*> interpolation;
 		FTextureID texture;
+		int flags;
+		PalEntry SpecialColors[2];
 
 		void InitFrom(const part &other)
 		{
@@ -1281,6 +1305,28 @@ struct side_t
 		textures[which].yScale *= delta;
 	}
 
+	void SetSpecialColor(int which, int slot, int r, int g, int b)
+	{
+		textures[which].SpecialColors[slot] = PalEntry(255, r, g, b);
+	}
+
+	void SetSpecialColor(int which, int slot, PalEntry rgb)
+	{
+		rgb.a = 255;
+		textures[which].SpecialColors[slot] = rgb;
+	}
+
+	// Note that the sector being passed in here may not be the actual sector this sidedef belongs to
+	// (either for polyobjects or FakeFlat'ed temporaries.)
+	PalEntry GetSpecialColor(int which, int slot, sector_t *frontsector) const
+	{
+		auto &part = textures[which];
+		if (part.flags & part::NoGradient) slot = 0;
+		if (part.flags & part::FlipGradient) slot ^= 1;
+		return (part.flags & part::UseOwnColors) ? part.SpecialColors[slot] : frontsector->SpecialColors[sector_t::walltop + slot];
+	}
+
+
 	DInterpolation *SetInterpolation(int position);
 	void StopInterpolation(int position);
 

wadsrc/static/shaders/glsl/main.fp

@@ -1,5 +1,6 @@
 in vec4 pixelpos;
 in vec3 glowdist;
+in vec3 gradientdist;
 
 in vec4 vWorldNormal;
 in vec4 vEyeNormal;
@@ -90,7 +91,7 @@ vec4 getTexel(vec2 st)
 			break;
 	}
 	if (uObjectColor2.a == 0.0) texel *= uObjectColor;
-	else texel *= mix(uObjectColor, uObjectColor2, glowdist.z);
+	else texel *= mix(uObjectColor, uObjectColor2, gradientdist.z);
 
 	return desaturate(texel);
 }

wadsrc/static/shaders/glsl/main.vp

@@ -7,6 +7,7 @@ in vec4 aVertex2;
 in vec4 aNormal;
 out vec4 pixelpos;
 out vec3 glowdist;
+out vec3 gradientdist;
 
 out vec4 vWorldNormal;
 out vec4 vEyeNormal;
@@ -50,16 +51,28 @@ void main()
 		pixelpos.xyz = worldcoord.xyz;
 		pixelpos.w = -eyeCoordPos.z/eyeCoordPos.w;
 
-		float topatpoint = -((uGlowTopPlane.w + uGlowTopPlane.x * worldcoord.x + uGlowTopPlane.y * worldcoord.z) * uGlowTopPlane.z);
+		if (uGlowTopColor.a > 0 || uGlowBottomColor.a > 0)
-		float bottomatpoint = -((uGlowBottomPlane.w + uGlowBottomPlane.x * worldcoord.x + uGlowBottomPlane.y * worldcoord.z) * uGlowBottomPlane.z);
+		{
+			float topatpoint = (uGlowTopPlane.w + uGlowTopPlane.x * worldcoord.x + uGlowTopPlane.y * worldcoord.z) * uGlowTopPlane.z;
+			float bottomatpoint = (uGlowBottomPlane.w + uGlowBottomPlane.x * worldcoord.x + uGlowBottomPlane.y * worldcoord.z) * uGlowBottomPlane.z;
 			glowdist.x = topatpoint - worldcoord.y;
 			glowdist.y = worldcoord.y - bottomatpoint;
 			glowdist.z = clamp(glowdist.x / (topatpoint - bottomatpoint), 0.0, 1.0);
+		}
+		
+		if (uObjectColor2.a != 0)
+		{
+			float topatpoint = (uGradientTopPlane.w + uGradientTopPlane.x * worldcoord.x + uGradientTopPlane.y * worldcoord.z) * uGradientTopPlane.z;
+			float bottomatpoint = (uGradientBottomPlane.w + uGradientBottomPlane.x * worldcoord.x + uGradientBottomPlane.y * worldcoord.z) * uGradientBottomPlane.z;
+			gradientdist.x = topatpoint - worldcoord.y;
+			gradientdist.y = worldcoord.y - bottomatpoint;
+			gradientdist.z = clamp(gradientdist.x / (topatpoint - bottomatpoint), 0.0, 1.0);
+		}
 		
 		if (uSplitBottomPlane.z != 0.0)
 		{
-			gl_ClipDistance[3] = -((uSplitTopPlane.w + uSplitTopPlane.x * worldcoord.x + uSplitTopPlane.y * worldcoord.z) * uSplitTopPlane.z) - worldcoord.y;
+			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);
+			gl_ClipDistance[4] = worldcoord.y - ((uSplitBottomPlane.w + uSplitBottomPlane.x * worldcoord.x + uSplitBottomPlane.y * worldcoord.z) * uSplitBottomPlane.z);
 		}
 
 		vWorldNormal = NormalModelMatrix * vec4(normalize(aNormal.xyz), 1.0);