diff options
Diffstat (limited to 'src/fdgl.hpp')
| -rw-r--r-- | src/fdgl.hpp | 47 |
1 files changed, 34 insertions, 13 deletions
diff --git a/src/fdgl.hpp b/src/fdgl.hpp index 42b3538..084ebed 100644 --- a/src/fdgl.hpp +++ b/src/fdgl.hpp @@ -16,9 +16,8 @@ #include <float.h> #include <math.h> -static const double SPRING_K = 16.0; -static const double CHARGE_KE = 40000.0; -static const double AREA_WEIGHT = 0.5; +static const double SPRING_K = 10.0; +static const double CHARGE_KE = 50000000.0; struct Region { Vector pos; @@ -52,6 +51,13 @@ vec_mult(const Vector& a, const Vector& b) return a.x * b.x + a.y * b.y; } +/** Magnitude. */ +inline double +vec_mag(const Vector& vec) +{ + return sqrt(vec.x * vec.x + vec.y * vec.y); +} + /** Reciprocal of magnitude. */ inline double vec_rmag(const Vector& vec) @@ -64,9 +70,9 @@ inline Vector spring_force(const Vector& a, const Vector& b, double length, double k) { const Vector vec = vec_sub(b, a); - const double rmag = vec_rmag(vec); - const double displacement = length - (1.0 / rmag); - return vec_mult(vec, rmag * k * displacement * 0.5); + const double mag = vec_mag(vec); + const double displacement = length - mag; + return vec_mult(vec, k * displacement * 0.5 / mag); } /** Spring force with a directional force to align with flow direction. */ @@ -80,14 +86,29 @@ edge_force(const Vector& dir, return vec_add(dir, spring_force(hpos, tpos, length, k)); } -/** Modified Coulomb's law */ +/** Constant tide force, does not vary with distance. */ +inline Vector +tide_force(const Vector& a, const Vector& b, double power) +{ + static const double G = 0.0000000000667; + const Vector vec = vec_sub(a, b); + const double mag = vec_mag(vec); + return vec_mult(vec, G * power / mag); +} + +/** + Repelling charge force. + + Many FDGL algorithms use charge according to Coulomb's law, but here we use + an inverse cube (not squared) law so influence drops off more rapidly with + distance. This, in conjunction with a tide, keeps the layout compact. +*/ inline Vector repel_force(const Region& a, const Region& b) { - const Vector vec = vec_mult(vec_sub(a.pos, b.pos), 4.0); - const double rmag = vec_rmag(vec); - const Vector a_weight = vec_mult(a.area, AREA_WEIGHT); - const Vector b_weight = vec_mult(b.area, AREA_WEIGHT); - const Vector force = vec_mult(vec, rmag * rmag * rmag * CHARGE_KE * 0.5); - return vec_mult(force, vec_mult(a_weight, b_weight)); + const Vector vec = vec_sub(a.pos, b.pos); + const double mag = vec_mag(vec); + const Vector force = vec_mult( + vec, (CHARGE_KE * 0.5 / (mag * mag * mag * mag * mag))); + return vec_mult(force, vec_mult(a.area, b.area)); } |