From 23d0d70ea65a997ee855e80ea000fc2b538a4d32 Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@zdoom.fake>
Date: Tue, 17 Nov 2009 13:50:46 +0000
Subject: [PATCH] - fixed: R_PointToAngle could overflow with very long vectors
 passed to   it. This caused rendering bugs on some maps. (Interestingly the
 only   other port having a safeguard for this in place was PrBoom.)

SVN r1985 (trunk)
---
 docs/rh-log.txt |  3 ++
 src/r_main.cpp  | 95 ++++++++++++++++++++++++++++---------------------
 2 files changed, 57 insertions(+), 41 deletions(-)

diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index c1c2593d2..453bdf4d9 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,4 +1,7 @@
 November 17, 2009  (Changes by Graf Zahl)
+- fixed: R_PointToAngle could overflow with very long vectors passed to 
+  it. This caused rendering bugs on some maps. (Interestingly the only
+  other port having a safeguard for this in place was PrBoom.)
 - reverted the change that makes 0-damage projectiles call P_DamageMobj.
   Both Hexen and Heretic depend on such projectiles not doing it as do many
   mods that create snow/rain effects plus any terrain splash mod.
diff --git a/src/r_main.cpp b/src/r_main.cpp
index bcec61c73..e960c7c5c 100644
--- a/src/r_main.cpp
+++ b/src/r_main.cpp
@@ -264,58 +264,71 @@ angle_t R_PointToAngle2 (fixed_t x1, fixed_t y1, fixed_t x, fixed_t y)
 		return 0;
 	}
 
-	if (x >= 0)
+	// We need to be aware of overflows here. If the values get larger than INT_MAX/4
+	// this code won't work anymore.
+
+	if (x < INT_MAX/4 && x > -INT_MAX/4 && y < INT_MAX/4 && y > -INT_MAX/4)
 	{
-		if (y >= 0)
+		if (x >= 0)
 		{
-			if (x > y)
-			{ // octant 0
-				return SlopeDiv(y, x);
+			if (y >= 0)
+			{
+				if (x > y)
+				{ // octant 0
+					return SlopeDiv(y, x);
+				}
+				else
+				{ // octant 1
+					return ANG90 - 1 - SlopeDiv(x, y);
+				}
 			}
-			else
-			{ // octant 1
-				return ANG90 - 1 - SlopeDiv(x, y);
+			else // y < 0
+			{
+				y = -y;
+				if (x > y)
+				{ // octant 8
+					return 0 - SlopeDiv(y, x);
+				}
+				else
+				{ // octant 7
+					return ANG270 + SlopeDiv(x, y);
+				}
 			}
 		}
-		else // y < 0
+		else // x < 0
 		{
-			y = -y;
-			if (x > y)
-			{ // octant 8
-				return 0 - SlopeDiv(y, x);
+			x = -x;
+			if (y >= 0)
+			{
+				if (x > y)
+				{ // octant 3
+					return ANG180 - 1 - SlopeDiv(y, x);
+				}
+				else
+				{ // octant 2
+					return ANG90 + SlopeDiv(x, y);
+				}
 			}
-			else
-			{ // octant 7
-				return ANG270 + SlopeDiv(x, y);
+			else // y < 0
+			{
+				y = -y;
+				if (x > y)
+				{ // octant 4
+					return ANG180 + SlopeDiv(y, x);
+				}
+				else
+				{ // octant 5
+					return ANG270 - 1 - SlopeDiv(x, y);
+				}
 			}
 		}
 	}
-	else // x < 0
+	else
 	{
-		x = -x;
-		if (y >= 0)
-		{
-			if (x > y)
-			{ // octant 3
-				return ANG180 - 1 - SlopeDiv(y, x);
-			}
-			else
-			{ // octant 2
-				return ANG90 + SlopeDiv(x, y);
-			}
-		}
-		else // y < 0
-		{
-			y = -y;
-			if (x > y)
-			{ // octant 4
-				return ANG180 + SlopeDiv(y, x);
-			}
-			else
-			{ // octant 5
-				return ANG270 - 1 - SlopeDiv(x, y);
-			}
-		}
+		// we have to use the slower but more precise floating point atan2 function here.
+		// (use quickertoint to speed this up because the CRT's conversion is rather slow and
+		//  this is used in time critical code.)
+		return quickertoint((float)(atan2f(float(y-viewy), float(x-viewx)) * (ANGLE_180/M_PI)));
 	}
 }