/* Builds the pressure right hand side as the negative divergence */
void buildRhs() {
double scale = 1.0/_hx;
for (int y = 0, idx = 0; y < _h; y++) {
for (int x = 0; x < _w; x++, idx++) {
_r[idx] = -scale*(_u->at(x + 1, y) - _u->at(x, y) +
_v->at(x, y + 1) - _v->at(x, y));
}
}
}
/* Applies the computed pressure to the velocity field */
void applyPressure(double timestep) {
double scale = timestep/(_density*_hx);
for (int y = 0, idx = 0; y < _h; y++) {
for (int x = 0; x < _w; x++, idx++) {
_u->at(x, y ) -= scale*_p[idx];
_u->at(x + 1, y ) += scale*_p[idx];
_v->at(x, y ) -= scale*_p[idx];
_v->at(x, y + 1) += scale*_p[idx];
}
}
for (int y = 0; y < _h; y++)
_u->at(0, y) = _u->at(_w, y) = 0.0;
for (int x = 0; x < _w; x++)
_v->at(x, 0) = _v->at(x, _h) = 0.0;
}