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Expose function for determining if tendons should be drawn using a catenary.

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PiperOrigin-RevId: 931170146
Change-Id: Ia3352a3e2bdc5e4df932e9d476e1e34200b62df1
This commit is contained in:
Haroon Qureshi
2026-06-12 08:44:48 -07:00
committed by Copybara-Service
parent 4bb02e299d
commit 0ea9c7cb3a
2 changed files with 61 additions and 47 deletions
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src/engine/engine_vis_visualize.c
+57 -47
View File
@@ -1083,6 +1083,61 @@ static void addSiteGeoms(const mjModel* m, mjData* d, const mjvOption* vopt,
}
int mjv_isCatenary(const mjModel* m, const mjData* d, int i, mjtNum* length) {
int has_stiffness = m->tendon_stiffness[i] ||
!mju_isZero(m->tendon_stiffnesspoly+mjNPOLY*i, mjNPOLY);
// tendon has a deadband spring
int limitedspring =
has_stiffness && // positive stiffness
m->tendon_lengthspring[2*i] == 0 && // range lower-bound is 0
m->tendon_lengthspring[2*i+1] > 0; // range upper-bound is positive
// tendon has a simple length constraint, but is currently not limited
mjtNum ten_length = d->ten_length[i];
mjtNum lower = m->tendon_range[2*i];
mjtNum upper = m->tendon_range[2*i + 1];
int limitedconstraint =
!has_stiffness && // zero stiffness
m->tendon_limited[i] == 1 && // limited length range
lower == 0 && // range lower-bound is 0
ten_length < upper; // current length is smaller than upper bound
int has_damping = m->tendon_damping[i] || !mju_isZero(m->tendon_dampingpoly+mjNPOLY*i, mjNPOLY);
// conditions for drawing a catenary
int draw_catenary =
!mjDISABLED(mjDSBL_GRAVITY) && // gravity enabled
mju_norm3(m->opt.gravity) > mjMINVAL && // gravity strictly nonzero
m->tendon_num[i] == 2 && // only two sites on the tendon
(limitedspring != limitedconstraint) && // either spring or constraint length limits
!has_damping && // no damping
m->tendon_frictionloss[i] == 0; // no frictionloss
// no actuator
if (draw_catenary) {
for (int j=0; j < m->nu; j++) {
if (m->actuator_trntype[j] == mjTRN_TENDON && m->actuator_trnid[2*j] == i) {
draw_catenary = 0;
break;
}
}
}
if (draw_catenary) {
// length of the tendon
if (limitedconstraint) {
*length = m->tendon_range[2*i+1];
} else {
*length = m->tendon_lengthspring[2*i+1];
}
}
return draw_catenary;
}
static void addSpatialTendonGeoms(const mjModel* m, mjData* d, const mjvOption* vopt, int catmask,
mjvScene* scn) {
const int category = mjCAT_DYNAMIC;
@@ -1098,45 +1153,8 @@ static void addSpatialTendonGeoms(const mjModel* m, mjData* d, const mjvOption*
continue;
}
int has_stiffness = m->tendon_stiffness[i] ||
!mju_isZero(m->tendon_stiffnesspoly+mjNPOLY*i, mjNPOLY);
// tendon has a deadband spring
int limitedspring =
has_stiffness && // positive stiffness
m->tendon_lengthspring[2*i] == 0 && // range lower-bound is 0
m->tendon_lengthspring[2*i+1] > 0; // range upper-bound is positive
// tendon has a simple length constraint, but is currently not limited
mjtNum ten_length = d->ten_length[i];
mjtNum lower = m->tendon_range[2*i];
mjtNum upper = m->tendon_range[2*i + 1];
int limitedconstraint =
!has_stiffness && // zero stiffness
m->tendon_limited[i] == 1 && // limited length range
lower == 0 && // range lower-bound is 0
ten_length < upper; // current length is smaller than upper bound
int has_damping = m->tendon_damping[i] || !mju_isZero(m->tendon_dampingpoly+mjNPOLY*i, mjNPOLY);
// conditions for drawing a catenary
int draw_catenary =
!mjDISABLED(mjDSBL_GRAVITY) && // gravity enabled
mju_norm3(m->opt.gravity) > mjMINVAL && // gravity strictly nonzero
m->tendon_num[i] == 2 && // only two sites on the tendon
(limitedspring != limitedconstraint) && // either spring or constraint length limits
!has_damping && // no damping
m->tendon_frictionloss[i] == 0; // no frictionloss
// no actuator
if (draw_catenary) {
for (int j=0; j < m->nu; j++) {
if (m->actuator_trntype[j] == mjTRN_TENDON && m->actuator_trnid[2*j] == i) {
draw_catenary = 0;
break;
}
}
}
mjtNum length;
int draw_catenary = mjv_isCatenary(m, d, i, &length);
// conditions not met: draw straight lines
if (!draw_catenary) {
@@ -1213,14 +1231,6 @@ static void addSpatialTendonGeoms(const mjModel* m, mjData* d, const mjvOption*
mju_copy3(x0, d->wrap_xpos + 3*d->ten_wrapadr[i]);
mju_copy3(x1, d->wrap_xpos + 3*d->ten_wrapadr[i] + 3);
// length of the tendon
mjtNum length;
if (limitedconstraint) {
length = m->tendon_range[2*i+1];
} else {
length = m->tendon_lengthspring[2*i+1];
}
// get number of points along catenary path (capped at 100)
int ncatenary = mjMIN(m->vis.quality.numslices + 1, 100);
mjtNum catenary[300];
src/engine/engine_vis_visualize.h
+4
View File
@@ -65,6 +65,10 @@ MJAPI void mjv_cameraFrame(mjtNum headpos[3], mjtNum forward[3], mjtNum up[3], m
MJAPI void mjv_cameraFrustum(float zver[2], float zhor[2], float zclip[2], const mjModel* m,
const mjvCamera* cam);
// determines if tendon should be rendered as a catenary curve and, if so, computes its length
MJAPI int mjv_isCatenary(const mjModel* m, const mjData* d, int i, mjtNum* length);
// computes points along a catenary curve
int mjv_catenary(const mjtNum x0[3], const mjtNum x1[3], const mjtNum gravity[3], mjtNum length,
mjtNum* catenary, int ncatenary);