- fixed depth buffer use of slope sprites.

They cannot be treated like perfectly horizontal floor sprites and need to write to the depth buffer in the same pass as the regular pixels.

source/core/rendering/scene/hw_drawinfo.cpp

@@ -540,6 +540,7 @@ void HWDrawInfo::RenderScene(FRenderState &state)
 	state.SetColorMask(true);
 
 	state.SetDepthBias(-1, -128);
+	drawlists[GLDL_MASKEDSLOPEFLATS].DrawFlats(this, state, false);
 	state.SetDepthMask(false);
 	drawlists[GLDL_MASKEDFLATS].DrawFlats(this, state, false);
 	state.SetDepthMask(true);

source/core/rendering/scene/hw_drawinfo.h

@@ -77,6 +77,7 @@ enum DrawListType
 	GLDL_MASKEDWALLSV,	// vertical wall sprites
 	GLDL_MASKEDWALLSH,  // horizontal wall sprites. These two lists merely exist for easier sorting.
 	GLDL_MASKEDFLATS,
+	GLDL_MASKEDSLOPEFLATS,
 	GLDL_MODELS,
 
 	GLDL_TRANSLUCENT,

source/core/rendering/scene/hw_drawlistadd.cpp

@@ -104,7 +104,7 @@ void HWDrawInfo::AddFlat(HWFlat *flat)
 	}
 	else
 	{
-		list = flat->Sprite ? GLDL_MASKEDFLATS : GLDL_PLAINFLATS;
+		list = flat->Sprite ? ((flat->Sprite->clipdist & TSPR_SLOPESPRITE)? GLDL_MASKEDSLOPEFLATS : GLDL_MASKEDFLATS) : GLDL_PLAINFLATS;
 	}
 	auto newflat = drawlists[list].NewFlat(slopespr);
 	*newflat = *flat;