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Cloth: allow forces to act parallel to cloth.

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Currently all force effectors can only act on cloth when the force is
perpendicular to the surface. This makes sense for wind, but not for
other forces; and the user may want even wind to have some friction.

This changes effector code to output two force vectors - although
you of course can pass the same pointer for both. The force is split
between the two outputs based on a new per-effector setting.

Differential Revision: https://developer.blender.org/D8017
This commit is contained in:
Alexander Gavrilov
2020-06-12 21:33:38 +03:00
parent f382109f38
commit 9e70129952
16 changed files with 155 additions and 36 deletions
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63
source/blender/physics/intern/implicit_blender.c
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@@ -1469,22 +1469,71 @@ void BPH_mass_spring_force_face_wind(
Implicit_Data *data, int v1, int v2, int v3, const float (*winvec)[3])
{
const float effector_scale = 0.02f;
int vs[3] = {v1, v2, v3};
float win[3], nor[3], area;
float factor;
float factor, base_force;
float force[3];
/* calculate face normal and area */
area = calc_nor_area_tri(nor, data->X[v1], data->X[v2], data->X[v3]);
/* The force is calculated and split up evenly for each of the three face verts */
factor = effector_scale * area / 3.0f;
world_to_root_v3(data, v1, win, winvec[v1]);
madd_v3_v3fl(data->F[v1], nor, factor * dot_v3v3(win, nor));
/* Calculate wind pressure at each vertex by projecting the wind field on the normal. */
for (int i = 0; i < 3; i++) {
world_to_root_v3(data, vs[i], win, winvec[vs[i]]);
world_to_root_v3(data, v2, win, winvec[v2]);
madd_v3_v3fl(data->F[v2], nor, factor * dot_v3v3(win, nor));
force[i] = dot_v3v3(win, nor);
}
world_to_root_v3(data, v3, win, winvec[v3]);
madd_v3_v3fl(data->F[v3], nor, factor * dot_v3v3(win, nor));
/* Compute per-vertex force values from local pressures.
* From integrating the pressure over the triangle and deriving
* equivalent vertex forces, it follows that:
*
* force[idx] = (sum(pressure) + pressure[idx]) * area / 12
*
* Effectively, 1/4 of the pressure acts just on its vertex,
* while 3/4 is split evenly over all three.
*/
mul_v3_fl(force, factor / 4.0f);
base_force = force[0] + force[1] + force[2];
/* add pressure to each of the face verts */
madd_v3_v3fl(data->F[v1], nor, base_force + force[0]);
madd_v3_v3fl(data->F[v2], nor, base_force + force[1]);
madd_v3_v3fl(data->F[v3], nor, base_force + force[2]);
}
void BPH_mass_spring_force_face_extern(
Implicit_Data *data, int v1, int v2, int v3, const float (*forcevec)[3])
{
const float effector_scale = 0.02f;
int vs[3] = {v1, v2, v3};
float nor[3], area;
float factor, base_force[3];
float force[3][3];
/* calculate face normal and area */
area = calc_nor_area_tri(nor, data->X[v1], data->X[v2], data->X[v3]);
/* The force is calculated and split up evenly for each of the three face verts */
factor = effector_scale * area / 3.0f;
/* Compute common and per-vertex force vectors from the original inputs. */
zero_v3(base_force);
for (int i = 0; i < 3; i++) {
world_to_root_v3(data, vs[i], force[i], forcevec[vs[i]]);
mul_v3_fl(force[i], factor / 4.0f);
add_v3_v3(base_force, force[i]);
}
/* Apply the common and vertex components to all vertices. */
for (int i = 0; i < 3; i++) {
add_v3_v3(force[i], base_force);
add_v3_v3(data->F[vs[i]], force[i]);
}
}
float BPH_tri_tetra_volume_signed_6x(Implicit_Data *data, int v1, int v2, int v3)