From 1f49908a6f271ddfefa117cdb1cc69742d95d1aa Mon Sep 17 00:00:00 2001
From: twinaphex <libretro@gmail.com>
Date: Sun, 28 Jul 2019 18:13:28 +0200
Subject: [PATCH] Backport
 https://github.com/Ferk/libretro-prboom/commit/ca2107f8a33b6dce5face9a290862d96ebf9c6e8
 - wiggle fix now also fixes flats/floors

---
 src/r_main.c  |  3 +++
 src/r_main.h  |  4 ++--
 src/r_plane.c | 50 +++++++++++++++++++++++++++++++++++---------------
 3 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/src/r_main.c b/src/r_main.c
index 6e41218..12169f9 100644
--- a/src/r_main.c
+++ b/src/r_main.c
@@ -78,6 +78,7 @@ angle_t  viewangle;
 angle_t  viewpitch;
 fixed_t  viewcos, viewsin;
 player_t *viewplayer;
+float viewfocratio; /*e6y: for more precise flat drawing */
 fixed_t  focallength;
 int      fieldofview;
 fixed_t  freelookviewheight;
@@ -441,6 +442,8 @@ void R_ExecuteSetViewSize (void)
 // proff 11/06/98: Added for high-res
   projectiony = ((SCREENHEIGHT * centerx * 320) / 200) / SCREENWIDTH * FRACUNIT;
 
+  /*  e6y: this is a precalculated value for more precise flats drawing (see R_MapPlane) */
+  viewfocratio = 1.6f / ((float)SCREENWIDTH / (float)SCREENHEIGHT);
   R_InitBuffer (scaledviewwidth, viewheight);
 
   R_InitTextureMapping();
diff --git a/src/r_main.h b/src/r_main.h
index d943299..2198041 100644
--- a/src/r_main.h
+++ b/src/r_main.h
@@ -52,9 +52,9 @@ extern fixed_t  centeryfrac;
 extern fixed_t  viewheightfrac; //e6y: for correct clipping of things
 extern fixed_t  freelookviewheight;
 extern fixed_t  projection;
-// proff 11/06/98: Added for high-res
-extern fixed_t  projectiony;
+extern fixed_t  projectiony; /* proff 11/06/98: Added for high-res */
 extern int      validcount;
+extern float    viewfocratio; /* e6y: for more precise flat drawing */
 extern fixed_t skyiscale;
 
 //
diff --git a/src/r_plane.c b/src/r_plane.c
index 72b6b47..b0dfa5c 100644
--- a/src/r_plane.c
+++ b/src/r_plane.c
@@ -104,6 +104,9 @@ static fixed_t xoffs,yoffs;    // killough 2/28/98: flat offsets
 
 fixed_t yslope[MAX_SCREENHEIGHT], distscale[MAX_SCREENWIDTH];
 
+/* forward declarations */
+extern boolean r_wiggle_fix;
+
 //
 // R_InitPlanes
 // Only at game startup.
@@ -134,27 +137,44 @@ static void R_MapPlane(int y, int x1, int x2, draw_span_vars_t *dsvars)
    fixed_t distance, length;
    unsigned index;
 
-   if (planeheight != cachedheight[y])
+   if (!r_wiggle_fix)
    {
-      cachedheight[y] = planeheight;
-      distance = cacheddistance[y] = FixedMul (planeheight, yslope[y]);
-      dsvars->xstep = cachedxstep[y] = FixedMul (distance,basexscale);
-      dsvars->ystep = cachedystep[y] = FixedMul (distance,baseyscale);
+      if (planeheight != cachedheight[y])
+      {
+         cachedheight[y] = planeheight;
+         distance = cacheddistance[y] = FixedMul (planeheight, yslope[y]);
+         dsvars->xstep = cachedxstep[y] = FixedMul (distance,basexscale);
+         dsvars->ystep = cachedystep[y] = FixedMul (distance,baseyscale);
+      }
+      else
+      {
+         distance = cacheddistance[y];
+         dsvars->xstep = cachedxstep[y];
+         dsvars->ystep = cachedystep[y];
+      }
+
+      length = FixedMul (distance,distscale[x1]);
+      angle = (viewangle + xtoviewangle[x1])>>ANGLETOFINESHIFT;
+
+      // killough 2/28/98: Add offsets
+      dsvars->xfrac =  viewx + FixedMul(finecosine[angle], length) + xoffs;
+      dsvars->yfrac = -viewy - FixedMul(finesine[angle],   length) + yoffs;
    }
    else
    {
-      distance = cacheddistance[y];
-      dsvars->xstep = cachedxstep[y];
-      dsvars->ystep = cachedystep[y];
+      float slope, realy;
+
+      distance = FixedMul (planeheight, yslope[y]);
+      slope = (float)(planeheight / 65535.0f / D_abs(centery - y));
+      realy = (float)distance / 65536.0f;
+
+      dsvars->xstep = (unsigned int)(viewsin * slope * viewfocratio);
+      dsvars->ystep = (unsigned int)(viewcos * slope * viewfocratio);
+
+      dsvars->xfrac =  viewx + xoffs + (int)(viewcos * realy) + (x1 - centerx) * dsvars->xstep;
+      dsvars->yfrac = -viewy + yoffs - (int)(viewsin * realy) + (x1 - centerx) * dsvars->ystep;
    }
 
-   length = FixedMul (distance,distscale[x1]);
-   angle = (viewangle + xtoviewangle[x1])>>ANGLETOFINESHIFT;
-
-   // killough 2/28/98: Add offsets
-   dsvars->xfrac =  viewx + FixedMul(finecosine[angle], length) + xoffs;
-   dsvars->yfrac = -viewy - FixedMul(finesine[angle],   length) + yoffs;
-
    if (drawvars.filterfloor == RDRAW_FILTER_LINEAR) {
       dsvars->xfrac -= (FRACUNIT>>1);
       dsvars->yfrac -= (FRACUNIT>>1);