star-cad

commit 632e64b00f456d80a36c384f6334d6a49d5be1a4
parent db7bfdf1058db9ac8b05308281a218fdd679ac20
Author: Christophe Coustet <christophe.coustet@meso-star.com>
Date:   Tue, 29 Jul 2025 13:47:24 +0200

Change the way get_centerofmass works

Now returns the true center of mass as a single point. Used to return a
list of centers, one by geometry's component.
The signature was changed accordingly.

Diffstat:
M
src/scad.h
 | 
6
++----
M
src/scad_geometry.c
 | 
41
++++++++++++++++++++++++++++++++---------

2 files changed, 34 insertions(+), 13 deletions(-)
diff --git a/src/scad.h b/src/scad.h
@@ -386,13 +386,11 @@ scad_geometry_get_mass
   (struct scad_geometry* geometry,
    double* mass);
 
-/* Get the center of mass of the various components of geometry `geometry'.
- * Note that `center' must be allocated by the caller with enough room for (at
- * least) 3 times the count of geom (scad_geometry_get_count) doubles. */
+/* Get the center of mass of geometry `geometry' in `center'. */
 SCAD_API res_T
 scad_geometry_get_centerofmass
   (struct scad_geometry* geometry,
-   double* center);
+   double center[3]);
 
 /* Get the `closest' point on geometry `geometry' from point `from'.
  * Return the `closest' point and its `distance'.
diff --git a/src/scad_geometry.c b/src/scad_geometry.c
@@ -807,10 +807,13 @@ error:
 res_T
 scad_geometry_get_centerofmass
   (struct scad_geometry* geom,
-   double* center)
+   double center[3])
 {
   res_T res = RES_OK;
-  size_t i = 0;
+  double *centers = NULL, *masses = NULL;
+  size_t i = 0, count;
+  struct mem_allocator* allocator;
+  int ierr;
 
   if(!geom || !center) {
     res = RES_BAD_ARG;
@@ -819,19 +822,39 @@ scad_geometry_get_centerofmass
 
   ERR(check_device(FUNC_NAME));
 
-  for(i = 0; i < geom->gmsh_dimTags_n; i += 2) {
-    double x, y, z;
-    int ierr = 0;
+  ASSERT(geom->gmsh_dimTags_n % 2 == 0);
+  count = geom->gmsh_dimTags_n / 2;
+  if(count == 1) {
     int dim = geom->gmsh_dimTags[i];
     int tag = geom->gmsh_dimTags[i + 1];
-    gmshModelOccGetCenterOfMass(dim, tag, &x, &y, &z, &ierr);
+    gmshModelOccGetCenterOfMass(dim, tag, center, center+1, center+2, &ierr);
     ERR(gmsh_err_to_res_T(ierr));
-    center[3*i] = x;
-    center[3*i + 1] = y;
-    center[3*i + 2] = z;
+  } else {
+    double c[3] = { 0, 0, 0 }, tmp[3], m = 0;
+    allocator = get_device()->allocator;
+    centers = MEM_ALLOC(allocator, count * 3 * sizeof(*centers));
+    masses = MEM_ALLOC(allocator, count * sizeof(*masses));
+    if(!centers || !masses) {
+      res = RES_MEM_ERR;
+      goto error;
+    }
+    for(i = 0; i < count; i++) {
+      int dim = geom->gmsh_dimTags[2*i];
+      int tag = geom->gmsh_dimTags[2*i + 1];
+      gmshModelOccGetCenterOfMass(dim, tag,
+          centers+3*i, centers+3*i+1, centers+3*i+2, &ierr);
+      ERR(gmsh_err_to_res_T(ierr));
+      gmshModelOccGetMass(dim, tag, masses+i, &ierr);
+      ERR(gmsh_err_to_res_T(ierr));
+      d3_add(c, c, d3_muld(tmp, centers+3*i, masses[i]));
+      m += masses[i];
+    }
+    d3_muld(center, c, 1/m);
   }
 
 exit:
+  if(centers) MEM_RM(allocator, centers);
+  if(masses) MEM_RM(allocator, masses);
   return res;
 error:
   goto exit;