--- a/trunk/chipmunkd/chipmunk.d	Thu Dec 09 22:25:04 2010 +0100
+++ b/trunk/chipmunkd/chipmunk.d	Fri Dec 10 02:10:27 2010 +0100
@@ -6,6 +6,7 @@
 import std.stdio;
 import std.string:format;
 import std.conv:to;
+import std.math:PI;
 
 void
 cpMessage(string message, string condition, string file, int line, bool isError)
@@ -92,8 +93,17 @@
 cpFloat
 cpMomentForCircle(cpFloat m, cpFloat r1, cpFloat r2, cpVect offset)
 {
-	return (1.0f/2.0f)*m*(r1*r1 + r2*r2) + m*cpvdot(offset, offset);
+	return m*(0.5f*(r1*r1 + r2*r2) + cpvlengthsq(offset));
 }
+
+/**
+	Calculate area of a hollow circle.
+*/
+cpFloat cpAreaForCircle(cpFloat r1, cpFloat r2)
+{
+	return 2.0f*cast(cpFloat)PI*cpfabs(r1*r1 - r2*r2);
+}
+
 /**
 	Calculate the moment of inertia for a line segment.
 	Beveling radius is not supported.
@@ -104,7 +114,16 @@
 	cpFloat length = cpvlength(cpvsub(b, a));
 	cpVect offset = cpvmult(cpvadd(a, b), 1.0f/2.0f);
 	
-	return m*length*length/12.0f + m*cpvdot(offset, offset);
+	return m*(length*length/12.0f + cpvlengthsq(offset));
+}
+
+/**
+	Calculate the area of a fattened (capsule shaped) line segment.
+*/
+cpFloat
+cpAreaForSegment(cpVect a, cpVect b, cpFloat r)
+{
+	return 2.0f*r*(cast(cpFloat)PI*r + cpvdist(a, b));
 }
 
 /**
@@ -135,6 +154,51 @@
 }
 
 /**
+	Calculate the signed area of a polygon.
+*/
+cpFloat cpAreaForPoly(const int numVerts, const cpVect *verts)
+{
+	cpFloat area = 0.0f;
+	for(int i=0; i<numVerts; i++){
+		area += cpvcross(verts[i], verts[(i+1)%numVerts]);
+	}
+	
+	return area/2.0f;
+}
+	
+/**
+	Calculate the natural centroid of a polygon.
+*/
+cpVect cpCentroidForPoly(const int numVerts, const cpVect *verts)
+{
+	cpFloat sum = 0.0f;
+	cpVect vsum = cpvzero;
+	
+	for(int i=0; i<numVerts; i++){
+		cpVect v1 = verts[i];
+		cpVect v2 = verts[(i+1)%numVerts];
+		cpFloat cross = cpvcross(v1, v2);
+		
+		sum += cross;
+		vsum = cpvadd(vsum, cpvmult(cpvadd(v1, v2), cross));
+	}
+	
+	return cpvmult(vsum, 1.0f/(3.0f*sum));
+}
+
+/**
+	Center the polygon on the origin. (Subtracts the centroid of the polygon from each vertex)
+*/
+void cpRecenterPoly(const int numVerts, cpVect *verts)
+{
+	cpVect centroid = cpCentroidForPoly(numVerts, verts);
+	
+	for(int i=0; i<numVerts; i++){
+		verts[i] = cpvsub(verts[i], centroid);
+	}
+}
+
+/**
 	Calculate the moment of inertia for a solid box.
 */
 cpFloat