From a7dc20e7d2d53dad20f41884f382bfedf8f1d44e Mon Sep 17 00:00:00 2001
From: Monster Iestyn <iestynjealous@ntlworld.com>
Date: Mon, 29 Aug 2016 22:42:06 +0100
Subject: [PATCH] Upper Unpegged on an FOF's control linedef now enables
 skewing of walls with respect to slopes

Skewing direction is decided per in-level wall by the Lower Unpegged flag on in-level linedefs themselves, since they already decide the stuff for FOF wall pegging as it is. That is unless Transfer Line is involved which moves everything to the control sector linedefs instead...
---
 src/r_segs.c | 73 +++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 64 insertions(+), 9 deletions(-)

diff --git a/src/r_segs.c b/src/r_segs.c
index 502ff3304..fff98dbf2 100644
--- a/src/r_segs.c
+++ b/src/r_segs.c
@@ -743,6 +743,12 @@ void R_RenderThickSideRange(drawseg_t *ds, INT32 x1, INT32 x2, ffloor_t *pfloor)
 	// Render FOF sides kinda like normal sides, with the frac and step and everything
 	// NOTE: INT64 instead of fixed_t because overflow concerns
 	INT64         top_frac, top_step, bottom_frac, bottom_step;
+	// skew FOF walls with slopes?
+	boolean	      slopeskew = false;
+	fixed_t       ffloortextureslide = 0;
+	INT32         oldx = -1;
+	fixed_t       left_top, left_bottom; // needed here for slope skewing
+	pslope_t      *skewslope = NULL;
 #endif
 
 	void (*colfunc_2s) (column_t *);
@@ -966,21 +972,68 @@ void R_RenderThickSideRange(drawseg_t *ds, INT32 x1, INT32 x2, ffloor_t *pfloor)
 	mceilingclip = ds->sprtopclip;
 	dc_texheight = textureheight[texnum]>>FRACBITS;
 
+#ifdef ESLOPE
+	// calculate both left ends
+	if (*pfloor->t_slope)
+		left_top = P_GetZAt(*pfloor->t_slope, ds->leftpos.x, ds->leftpos.y) - viewz;
+	else
+		left_top = *pfloor->topheight - viewz;
+
+	if (*pfloor->b_slope)
+		left_bottom = P_GetZAt(*pfloor->b_slope, ds->leftpos.x, ds->leftpos.y) - viewz;
+	else
+		left_bottom = *pfloor->bottomheight - viewz;
+	dc_texturemid = left_top;
+	skewslope = *pfloor->t_slope; // skew using top slope by default
+#else
 	dc_texturemid = *pfloor->topheight - viewz;
+#endif
 
 	if (newline)
 	{
 		offsetvalue = sides[newline->sidenum[0]].rowoffset;
 		if (newline->flags & ML_DONTPEGBOTTOM)
+#ifdef ESLOPE
+		{
+			dc_texturemid = left_bottom;
+			skewslope = *pfloor->b_slope; // skew using bottom slope
+		}
+#else
 			offsetvalue -= *pfloor->topheight - *pfloor->bottomheight;
+#endif
+#ifdef ESLOPE
+		if (newline->flags & ML_DONTPEGTOP)
+			slopeskew = true;
+#endif
 	}
 	else
 	{
 		offsetvalue = sides[pfloor->master->sidenum[0]].rowoffset;
 		if (curline->linedef->flags & ML_DONTPEGBOTTOM)
+#ifdef ESLOPE
+		{
+			dc_texturemid = left_bottom;
+			skewslope = *pfloor->b_slope; // skew using bottom slope
+		}
+#else
 			offsetvalue -= *pfloor->topheight - *pfloor->bottomheight;
+#endif
+#ifdef ESLOPE
+		if (pfloor->master->flags & ML_DONTPEGTOP) // use control linedef's flags
+			slopeskew = true;
+#endif
 	}
 
+#ifdef ESLOPE
+	if (slopeskew)
+	{
+		angle_t lineangle = R_PointToAngle2(curline->v1->x, curline->v1->y, curline->v2->x, curline->v2->y);
+
+		if (skewslope)
+			ffloortextureslide = FixedMul(skewslope->zdelta, FINECOSINE((lineangle-skewslope->xydirection)>>ANGLETOFINESHIFT));
+	}
+#endif
+
 	dc_texturemid += offsetvalue;
 
 	// Texture must be cached before setting colfunc_2s,
@@ -999,23 +1052,18 @@ void R_RenderThickSideRange(drawseg_t *ds, INT32 x1, INT32 x2, ffloor_t *pfloor)
 #ifdef ESLOPE
 	// Set heights according to plane, or slope, whichever
 	{
-		fixed_t left_top, right_top, left_bottom, right_bottom;
+		fixed_t right_top, right_bottom;
 
+		// calculate right ends now
 		if (*pfloor->t_slope)
-		{
-			left_top = P_GetZAt(*pfloor->t_slope, ds->leftpos.x, ds->leftpos.y) - viewz;
 			right_top = P_GetZAt(*pfloor->t_slope, ds->rightpos.x, ds->rightpos.y) - viewz;
-		}
 		else
-			left_top = right_top = *pfloor->topheight - viewz;
+			right_top = *pfloor->topheight - viewz;
 
 		if (*pfloor->b_slope)
-		{
-			left_bottom = P_GetZAt(*pfloor->b_slope, ds->leftpos.x, ds->leftpos.y) - viewz;
 			right_bottom = P_GetZAt(*pfloor->b_slope, ds->rightpos.x, ds->rightpos.y) - viewz;
-		}
 		else
-			left_bottom = right_bottom = *pfloor->bottomheight - viewz;
+			right_bottom = *pfloor->bottomheight - viewz;
 
 		// using INT64 to avoid 32bit overflow
 		top_frac =    (INT64)centeryfrac - (((INT64)left_top     * ds->scale1) >> FRACBITS);
@@ -1039,6 +1087,13 @@ void R_RenderThickSideRange(drawseg_t *ds, INT32 x1, INT32 x2, ffloor_t *pfloor)
 	{
 		if (maskedtexturecol[dc_x] != INT16_MAX)
 		{
+#ifdef ESLOPE
+			if (ffloortextureslide) { // skew FOF walls
+				if (oldx != -1)
+					dc_texturemid += FixedMul(ffloortextureslide, (maskedtexturecol[oldx]-maskedtexturecol[dc_x])<<FRACBITS);
+				oldx = dc_x;
+			}
+#endif
 			// SoM: New code does not rely on R_DrawColumnShadowed_8 which
 			// will (hopefully) put less strain on the stack.
 			if (dc_numlights)