From 2e5ada5f25a1e0908466940c06cd8f12abc93a58 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@users.noreply.github.com>
Date: Tue, 14 Feb 2017 18:20:21 +0100
Subject: [PATCH] - fixed texture clamping calculations for negative scales.

---
 src/gl/scene/gl_wall.h    |  2 +-
 src/gl/scene/gl_walls.cpp | 54 ++++++++++++++++++++++++++++-----------
 2 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/src/gl/scene/gl_wall.h b/src/gl/scene/gl_wall.h
index 7206c86c54..7337c4d3f4 100644
--- a/src/gl/scene/gl_wall.h
+++ b/src/gl/scene/gl_wall.h
@@ -192,7 +192,7 @@ private:
 	bool PutWallCompat(int passflag);
 	void PutWall(bool translucent);
 	void PutPortal(int ptype);
-	void CheckTexturePosition();
+	void CheckTexturePosition(FTexCoordInfo *tci);
 
 	void RenderFogBoundaryCompat();
 	void RenderLightsCompat(int pass);
diff --git a/src/gl/scene/gl_walls.cpp b/src/gl/scene/gl_walls.cpp
index 5965eebc38..fc5606b47f 100644
--- a/src/gl/scene/gl_walls.cpp
+++ b/src/gl/scene/gl_walls.cpp
@@ -626,7 +626,7 @@ bool GLWall::SetWallCoordinates(seg_t * seg, FTexCoordInfo *tci, float textureto
 //
 //==========================================================================
 
-void GLWall::CheckTexturePosition()
+void GLWall::CheckTexturePosition(FTexCoordInfo *tci)
 {
 	float sub;
 
@@ -634,23 +634,47 @@ void GLWall::CheckTexturePosition()
 
 	// clamp texture coordinates to a reasonable range.
 	// Extremely large values can cause visual problems
-	if (tcs[UPLFT].v < tcs[UPRGT].v)
+	if (tci->mScale.Y > 0)
 	{
-		sub = float(xs_FloorToInt(tcs[UPLFT].v));
+		if (tcs[UPLFT].v < tcs[UPRGT].v)
+		{
+			sub = float(xs_FloorToInt(tcs[UPLFT].v));
+		}
+		else
+		{
+			sub = float(xs_FloorToInt(tcs[UPRGT].v));
+		}
+		tcs[UPLFT].v -= sub;
+		tcs[UPRGT].v -= sub;
+		tcs[LOLFT].v -= sub;
+		tcs[LORGT].v -= sub;
+
+		if ((tcs[UPLFT].v == 0.f && tcs[UPRGT].v == 0.f && tcs[LOLFT].v <= 1.f && tcs[LORGT].v <= 1.f) ||
+			(tcs[UPLFT].v >= 0.f && tcs[UPRGT].v >= 0.f && tcs[LOLFT].v == 1.f && tcs[LORGT].v == 1.f))
+		{
+			flags |= GLT_CLAMPY;
+		}
 	}
 	else
 	{
-		sub = float(xs_FloorToInt(tcs[UPRGT].v));
-	}
-	tcs[UPLFT].v -= sub;
-	tcs[UPRGT].v -= sub;
-	tcs[LOLFT].v -= sub;
-	tcs[LORGT].v -= sub;
+		if (tcs[LOLFT].v < tcs[LORGT].v)
+		{
+			sub = float(xs_FloorToInt(tcs[LOLFT].v));
+		}
+		else
+		{
+			sub = float(xs_FloorToInt(tcs[LORGT].v));
+		}
+		tcs[UPLFT].v -= sub;
+		tcs[UPRGT].v -= sub;
+		tcs[LOLFT].v -= sub;
+		tcs[LORGT].v -= sub;
 
-	if ((tcs[UPLFT].v == 0.f && tcs[UPRGT].v == 0.f && tcs[LOLFT].v <= 1.f && tcs[LORGT].v <= 1.f) ||
-		(tcs[UPLFT].v >= 0.f && tcs[UPRGT].v >= 0.f && tcs[LOLFT].v == 1.f && tcs[LORGT].v == 1.f))
-	{
-		flags |= GLT_CLAMPY;
+		if ((tcs[LOLFT].v == 0.f && tcs[LORGT].v == 0.f && tcs[UPLFT].v <= 1.f && tcs[UPRGT].v <= 1.f) ||
+			(tcs[LOLFT].v >= 0.f && tcs[LORGT].v >= 0.f && tcs[UPLFT].v == 1.f && tcs[UPRGT].v == 1.f))
+		{
+			flags |= GLT_CLAMPY;
+		}
 	}
 
 	// Check if this is marked as a skybox and if so, do the same for x.
@@ -721,7 +745,7 @@ void GLWall::DoTexture(int _type,seg_t * seg, int peg,
 	else
 	{
 
-		CheckTexturePosition();
+		CheckTexturePosition(&tci);
 
 		// Add this wall to the render list
 		sector_t * sec = sub ? sub->sector : seg->frontsector;
@@ -1139,7 +1163,7 @@ void GLWall::BuildFFBlock(seg_t * seg, F3DFloor * rover,
 		tcs[LOLFT].v = tci.FloatToTexV(to - ff_bottomleft);
 		tcs[LORGT].v = tci.FloatToTexV(to - ff_bottomright);
 		type = RENDERWALL_FFBLOCK;
-		CheckTexturePosition();
+		CheckTexturePosition(&tci);
 	}
 
 	ztop[0] = ff_topleft;