From 1312df7fdcf9fceff63cf82bf97d6101c2c52215 Mon Sep 17 00:00:00 2001
From: Juan Linietsky <reduzio@gmail.com>
Date: Mon, 14 Dec 2015 09:06:53 -0300
Subject: [PATCH] implement point cloud function using convex hull for
 ConvexPolygonShape2D, fixes #2848

---
 core/math/geometry.h                        | 31 +++++++++++++++++++++
 scene/resources/convex_polygon_shape_2d.cpp |  6 +++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/core/math/geometry.h b/core/math/geometry.h
index b438b41d61e0..821489567603 100644
--- a/core/math/geometry.h
+++ b/core/math/geometry.h
@@ -886,7 +886,38 @@ class Geometry {
 	}
 
 
+	static double vec2_cross(const Point2 &O, const Point2 &A, const Point2 &B)
+	{
+		return (double)(A.x - O.x) * (B.y - O.y) - (double)(A.y - O.y) * (B.x - O.x);
+	}
+
+	// Returns a list of points on the convex hull in counter-clockwise order.
+	// Note: the last point in the returned list is the same as the first one.
+	static Vector<Point2> convex_hull_2d(Vector<Point2> P)
+	{
+		int n = P.size(), k = 0;
+		Vector<Point2> H;
+		H.resize(2*n);
+
+		// Sort points lexicographically
+		P.sort();
+
 
+		// Build lower hull
+		for (int i = 0; i < n; ++i) {
+			while (k >= 2 && vec2_cross(H[k-2], H[k-1], P[i]) <= 0) k--;
+			H[k++] = P[i];
+		}
+
+		// Build upper hull
+		for (int i = n-2, t = k+1; i >= 0; i--) {
+			while (k >= t && vec2_cross(H[k-2], H[k-1], P[i]) <= 0) k--;
+			H[k++] = P[i];
+		}
+
+		H.resize(k);
+		return H;
+	}
 
 	static MeshData build_convex_mesh(const DVector<Plane> &p_planes);
 	static DVector<Plane> build_sphere_planes(float p_radius, int p_lats, int p_lons, Vector3::Axis p_axis=Vector3::AXIS_Z);
diff --git a/scene/resources/convex_polygon_shape_2d.cpp b/scene/resources/convex_polygon_shape_2d.cpp
index a1137ba61449..86cf818ac355 100644
--- a/scene/resources/convex_polygon_shape_2d.cpp
+++ b/scene/resources/convex_polygon_shape_2d.cpp
@@ -30,6 +30,8 @@
 
 #include "servers/physics_2d_server.h"
 #include "servers/visual_server.h"
+#include "geometry.h"
+
 void ConvexPolygonShape2D::_update_shape() {
 
 	Physics2DServer::get_singleton()->shape_set_data(get_rid(),points);
@@ -40,7 +42,9 @@ void ConvexPolygonShape2D::_update_shape() {
 void ConvexPolygonShape2D::set_point_cloud(const Vector<Vector2>& p_points) {
 
 
-
+	Vector<Point2> hull=Geometry::convex_hull_2d(p_points);
+	ERR_FAIL_COND(hull.size()<3);
+	set_points(hull);
 }
 
 void ConvexPolygonShape2D::set_points(const Vector<Vector2>& p_points) {