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Differential D3655 Diff 11714 source/blender/physics/intern/implicit_blender.c

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source/blender/physics/intern/implicit_blender.c

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} }
bool BPH_mass_spring_force_spring_linear(Implicit_Data *data, int i, int j, float restlen, bool BPH_mass_spring_force_spring_linear(Implicit_Data *data, int i, int j, float restlen,
float stiffness, float damping, bool no_compress, float clamp_force) float stiffness_tension, float damping_tension,
float stiffness_compression, float damping_compression,
bool resist_compress, bool new_compress, float clamp_force)
{ {
float extent[3], length, dir[3], vel[3]; float extent[3], length, dir[3], vel[3];
float f[3], dfdx[3][3], dfdv[3][3];
float damping = 0;
// calculate elonglation // calculate elonglation
spring_length(data, i, j, extent, dir, &length, vel); spring_length(data, i, j, extent, dir, &length, vel);
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/* This code computes not only the force, but also its derivative. /* This code computes not only the force, but also its derivative.
Zero derivative effectively disables the spring for the implicit solver. Zero derivative effectively disables the spring for the implicit solver.
Thus length > restlen makes cloth unconstrained at the start of simulation. */ Thus length > restlen makes cloth unconstrained at the start of simulation. */
if ((length >= restlen && length > 0) || no_compress) { if ((length >= restlen && length > 0) || resist_compress) {
float stretch_force, f[3], dfdx[3][3], dfdv[3][3]; float stretch_force;
damping = damping_tension;
stretch_force = stiffness * (length - restlen); stretch_force = stiffness_tension * (length - restlen);
if (clamp_force > 0.0f && stretch_force > clamp_force) { if (clamp_force > 0.0f && stretch_force > clamp_force) {
stretch_force = clamp_force; stretch_force = clamp_force;
} }
mul_v3_v3fl(f, dir, stretch_force); mul_v3_v3fl(f, dir, stretch_force);
// Ascher & Boxman, p.21: Damping only during elonglation dfdx_spring(dfdx, dir, length, restlen, stiffness_tension);
// something wrong with it... }
madd_v3_v3fl(f, dir, damping * dot_v3v3(vel, dir)); else if (new_compress) {
/* this is based on the Choi and Ko bending model, which works surprisingly well for compression. */
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Code style: comments start with capital letter and end with a dot.

brecht: Code style: comments start with capital letter and end with a dot.
float kb = stiffness_compression;
float cb = kb; /* cb equal to kb seems to work, but a factor can be added if necessary */
dfdx_spring(dfdx, dir, length, restlen, stiffness); damping = damping_compression;
dfdv_damp(dfdv, dir, damping);
apply_spring(data, i, j, f, dfdx, dfdv); mul_v3_v3fl(f, dir, fbstar(length, restlen, kb, cb));
return true; outerproduct(dfdx, dir, dir);
mul_m3_fl(dfdx, fbstar_jacobi(length, restlen, kb, cb));
} }
else { else {
return false; return false;
} }
madd_v3_v3fl(f, dir, damping * dot_v3v3(vel, dir));
dfdv_damp(dfdv, dir, damping);
apply_spring(data, i, j, f, dfdx, dfdv);
return true;
} }
/* See "Stable but Responsive Cloth" (Choi, Ko 2005) *//* See "Stable but Responsive Cloth" (Choi, Ko 2005) */
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