Recast: add helper function to calculate slope angle from 2 points

src/thirdparty/recast/Shared/Include/SharedCommon.h

@@ -386,6 +386,12 @@ inline bool rdOverlapBounds(const float* amin, const float* amax,
 	return overlap;
 }
 
+/// Derives the slope angle from 2 points.
+///  @param[in]		v1	The start vector. [(x, y, z)]
+///  @param[in]		v2	The end vector. [(x, y, z)]
+/// @return The slope angle between the 2 points.
+float rdCalcSlopeAngle(const float* v1, const float* v2);
+
 /// Derives the closest point on a triangle from the specified reference point.
 ///  @param[out]	closest	The closest point on the triangle.	
 ///  @param[in]		p		The reference point from which to test. [(x, y, z)]

src/thirdparty/recast/Shared/Source/SharedCommon.cpp

@@ -21,6 +21,19 @@
 
 //////////////////////////////////////////////////////////////////////////////////////////
 
+float rdCalcSlopeAngle(const float* v1, const float* v2)
+{
+	const float deltaX = v2[0] - v1[0];
+	const float deltaY = v2[1] - v1[1];
+	const float deltaZ = v2[2] - v1[2];
+
+	const float horizontalDistance = rdMathSqrtf((deltaX*deltaX)+(deltaY*deltaY));
+	const float slopeAngleRadians = rdMathAtan2f(deltaZ, horizontalDistance);
+	const float slopeAngleDegrees = slopeAngleRadians*(180.0f/RD_PI);
+
+	return slopeAngleDegrees;
+}
+
 void rdClosestPtPointTriangle(float* closest, const float* p,
 							  const float* a, const float* b, const float* c)
 {