From: Daniel Karbach <daniel.karbach@localhorst.tv>
Date: Wed, 15 Jan 2014 08:40:08 +0000 (+0100)
Subject: better gravity calculation
X-Git-Url: http://git.localhorst.tv/?p=gworm.git;a=commitdiff_plain;h=e7e1f2a11255c3e0e76d86b2ea48e6d3bd5b1574

better gravity calculation
---

diff --git a/src/world/World.cpp b/src/world/World.cpp
index 206105b..53115dc 100644
--- a/src/world/World.cpp
+++ b/src/world/World.cpp
@@ -28,6 +28,8 @@ Entity &World::AddEntity(const Entity &e) {
 }
 
 
+// returns <1.37136364,1.37136734> for 1 mass at <0,0>
+/*
 Vector<float> World::ForceAt(Vector<float> p1, float m1) const {
 	Vector<float> force(0, 0);
 
@@ -48,5 +50,33 @@ Vector<float> World::ForceAt(Vector<float> p1, float m1) const {
 
 	return force;
 }
+*/
+
+// returns <1.37136674,1.37136662> for 1 mass at <0,0>
+// (should be less prone to rounding loss, i.e. more accurate)
+Vector<float> World::ForceAt(Vector<float> p1, float m1) const {
+	Vector<float> force(0, 0);
+
+	for (Vector<int> p2(0, 0); p2.y < size.y; ++p2.y) {
+		Vector<float> rowForce(0, 0);
+		for (p2.x = 0; p2.x < size.x; ++p2.x) {
+			const int i = Index(p2);
+			if (p1 == Vector<float>(p2)) continue;
+
+			const Vector<float> diff(Vector<float>(p2) - p1);
+			const Vector<float> dir(Norm(diff));
+
+			const float m2 = masses[i];
+			const float r2 = Dot(diff, diff);
+
+			const float mag = G * ((m1 * m2) / r2) * 2; // double because m2 is our reference frame
+
+			rowForce += dir * mag;
+		}
+		force += rowForce;
+	}
+
+	return force;
+}
 
 }