From: Francois Fleuret <francois@fleuret.org>
Date: Sat, 1 Apr 2017 21:09:31 +0000 (+0200)
Subject: Fixed a major bug in the border forces, and changed the dissipation model to max... 
X-Git-Url: https://fleuret.org/cgi-bin/gitweb/gitweb.cgi?p=flatland.git;a=commitdiff_plain;h=33bfa28983025c2387388e0e5f7d7bdd0ceb0f8a

Fixed a major bug in the border forces, and changed the dissipation model to max-speed one.
---

diff --git a/polygon.cc b/polygon.cc
index ba629c5..353486e 100644
--- a/polygon.cc
+++ b/polygon.cc
@@ -31,7 +31,7 @@ using namespace std;
 
 static const scalar_t dl = 20.0;
 static const scalar_t repulsion_constant = 0.2;
-static const scalar_t dissipation = 0.5;
+static const scalar_t speed_max = 1e2;
 
 Polygon::Polygon(scalar_t mass,
                  scalar_t red, scalar_t green, scalar_t blue,
@@ -306,17 +306,18 @@ void Polygon::initialize(int nb_polygons) {
 }
 
 bool Polygon::update(scalar_t dt) {
+  scalar_t speed = sqrt(_dcenter_x * _dcenter_x + _dcenter_y * _dcenter_y);
+  scalar_t speed_target = speed_max - exp(-speed / speed_max) * speed_max;
+
+  _dcenter_x = speed_target * _dcenter_x / speed;
+  _dcenter_y = speed_target * _dcenter_y / speed;
+
   if(!_nailed) {
     _center_x += _dcenter_x * dt;
     _center_y += _dcenter_y * dt;
     _theta += _dtheta * dt;
   }
 
-  scalar_t d = exp(log(dissipation) * dt);
-  _dcenter_x *= d;
-  _dcenter_y *= d;
-  _dtheta *= d;
-
   scalar_t vx = cos(_theta), vy = sin(_theta);
 
   for(int n = 0; n < _nb_vertices; n++) {
@@ -366,11 +367,15 @@ void Polygon::apply_border_forces(scalar_t dt,
       scalar_t x = _x[v] * (1 - s) + _x[vp] * s;
       scalar_t y = _y[v] * (1 - s) + _y[vp] * s;
       scalar_t vx = 0, vy = 0;
-      if(x < xmin) vx = xmin - x;
+      if(x < xmin) vx = x - xmin;
       else if(x > xmax) vx = x - xmax;
-      if(y < ymin) vy = ymin - y;
+      if(y < ymin) vy = y - ymin;
       else if(y > ymax) vy = y - ymax;
-      apply_force(dt, x, y, - dl * vx * repulsion_constant, - dl * vy * repulsion_constant);
+      if(vx != 0 || vy != 0) {
+        // cerr << "apply_border_forces vx = " << vx << " vy = " << vy << endl;
+        apply_force(dt, x, y,
+                    - dl * vx * repulsion_constant, - dl * vy * repulsion_constant);
+      }
     }
   }
 }