Merge pull request #102 from BIackthorn/feature-voxel-intersect

Implemented voxel-mesh intersection

xlb/operator/boundary_masker/mesh_boundary_masker.py

@@ -59,6 +59,94 @@ def index_to_position(index: wp.vec3i):
             pos = ijk + wp.vec3(0.5, 0.5, 0.5)  # cell center
             return pos
 
+        # Function to precompute useful values per triangle, assuming spacing is (1,1,1)
+        # inputs: verts: triangle vertices, normal: triangle unit normal
+        # outputs: dist1, dist2, normal_edge0, normal_edge1, dist_edge
+        @wp.func
+        def pre_compute(
+            verts: wp.mat33f,  # triangle vertices
+            normal: wp.vec3f,  # triangle normal
+        ):
+            corner = wp.vec3f(float(normal[0] > 0.0), float(normal[1] > 0.0), float(normal[2] > 0.0))
+
+            dist1 = wp.dot(normal, corner - verts[0])
+            dist2 = wp.dot(normal, wp.vec3f(1.0, 1.0, 1.0) - corner - verts[0])
+
+            edges = wp.transpose(wp.mat33(verts[1] - verts[0], verts[2] - verts[1], verts[0] - verts[2]))
+            normal_edge0 = wp.mat33f(0.0)
+            normal_edge1 = wp.mat33f(0.0)
+            dist_edge = wp.mat33f(0.0)
+
+            for axis0 in range(0, 3):
+                axis2 = (axis0 + 2) % 3
+
+                sgn = 1.0
+                if normal[axis2] < 0.0:
+                    sgn = -1.0
+
+                for i in range(0, 3):
+                    normal_edge0[i][axis0] = -1.0 * sgn * edges[i][axis0]
+                    normal_edge1[i][axis0] = sgn * edges[i][axis0]
+
+                    dist_edge[i][axis0] = (
+                        -1.0 * (normal_edge0[i][axis0] * verts[i][axis0] + normal_edge1[i][axis0] * verts[i][axis0])
+                        + wp.max(0.0, normal_edge0[i][axis0])
+                        + wp.max(0.0, normal_edge1[i][axis0])
+                    )
+
+            return dist1, dist2, normal_edge0, normal_edge1, dist_edge
+
+        # Check whether this triangle intersects the unit cube at position low
+        #  inputs: low: position of the cube, normal: triangle unit normal, dist1, dist2, normal_edge0, normal_edge1, dist_edge: precomputed values
+        #  outputs: True if intersection, False otherwise
+        #  reference: Fast parallel surface and solid voxelization on GPUs, M. Schwarz, H-P. Siedel, https://dl.acm.org/doi/10.1145/1882261.1866201
+        @wp.func
+        def triangle_box_intersect(
+            low: wp.vec3f,
+            normal: wp.vec3f,
+            dist1: wp.float32,
+            dist2: wp.float32,
+            normal_edge0: wp.mat33f,
+            normal_edge1: wp.mat33f,
+            dist_edge: wp.mat33f,
+        ):
+            if (wp.length(normal) > 0.0) and (wp.dot(normal, low) + dist1) * (wp.dot(normal, low) + dist2) <= 0.0:
+                intersect = True
+                #  Loop over primary axis for projection
+                for ax0 in range(0, 3):
+                    ax1 = (ax0 + 1) % 3
+                    for i in range(0, 3):
+                        intersect = intersect and (normal_edge0[i][ax0] * low[ax0] + normal_edge1[i][ax0] * low[ax1] + dist_edge[i][ax0] >= 0.0)
+
+                return intersect
+            else:
+                return False
+
+        # Check whether the unit voxel at position low intersects the warp mesh, assumes mesh has valid normals
+        #  inputs: mesh_id: mesh id, low: position of the voxel
+        #  outputs: True if intersection, False otherwise
+        @wp.func
+        def mesh_voxel_intersect(mesh_id: wp.uint64, low: wp.vec3):
+            query = wp.mesh_query_aabb(mesh_id, low, low + wp.vec3f(1.0, 1.0, 1.0))
+
+            for f in query:
+                v0 = wp.mesh_eval_position(mesh_id, f, 1.0, 0.0)
+                v1 = wp.mesh_eval_position(mesh_id, f, 0.0, 1.0)
+                v2 = wp.mesh_eval_position(mesh_id, f, 0.0, 0.0)
+                normal = wp.mesh_eval_face_normal(mesh_id, f)
+
+                v = wp.transpose(wp.mat33f(v0, v1, v2))
+
+                # TODO: run this on triangles in advance
+                dist1, dist2, normal_edge0, normal_edge1, dist_edge = pre_compute(verts=v, normal=normal)
+
+                if triangle_box_intersect(
+                    low=low, normal=normal, dist1=dist1, dist2=dist2, normal_edge0=normal_edge0, normal_edge1=normal_edge1, dist_edge=dist_edge
+                ):
+                    return True
+
+            return False
+
         # Construct the warp kernel
         # Do voxelization mesh query (warp.mesh_query_aabb) to find solid voxels
         #  - this gives an approximate 1 voxel thick surface around mesh
@@ -79,20 +167,16 @@ def kernel(
             pos_bc_cell = index_to_position(index)
             half = wp.vec3(0.5, 0.5, 0.5)
 
-            vox_query = wp.mesh_query_aabb(mesh_id, pos_bc_cell - half, pos_bc_cell + half)
-            face = wp.int32(0)
-            if wp.mesh_query_aabb_next(vox_query, face):
+            if mesh_voxel_intersect(mesh_id=mesh_id, low=pos_bc_cell - half):
                 # Make solid voxel
                 bc_mask[0, index[0], index[1], index[2]] = wp.uint8(255)
             else:
                 # Find the fractional distance to the mesh in each direction
                 for l in range(1, _q):
                     _dir = wp.vec3f(_c_float[0, l], _c_float[1, l], _c_float[2, l])
 
-                    # Check to see if this neighbor is solid
-                    vox_query_dir = wp.mesh_query_aabb(mesh_id, pos_bc_cell + _dir - half, pos_bc_cell + _dir + half)
-                    face = wp.int32(0)
-                    if wp.mesh_query_aabb_next(vox_query_dir, face):
+                    # Check to see if this neighbor is solid - this is super inefficient TODO: make it way better
+                    if mesh_voxel_intersect(mesh_id=mesh_id, low=pos_bc_cell + _dir - half):
                         # We know we have a solid neighbor
                         # Set the boundary id and missing_mask
                         bc_mask[0, index[0], index[1], index[2]] = wp.uint8(id_number)
@@ -109,9 +193,9 @@ def warp_implementation(
     ):
         assert bc.mesh_vertices is not None, f'Please provide the mesh vertices for {bc.__class__.__name__} BC using keyword "mesh_vertices"!'
         assert bc.indices is None, f"Please use IndicesBoundaryMasker operator if {bc.__class__.__name__} is imposed on known indices of the grid!"
-        assert (
-            bc.mesh_vertices.shape[1] == self.velocity_set.d
-        ), "Mesh points must be reshaped into an array (N, 3) where N indicates number of points!"
+        assert bc.mesh_vertices.shape[1] == self.velocity_set.d, (
+            "Mesh points must be reshaped into an array (N, 3) where N indicates number of points!"
+        )
         mesh_vertices = bc.mesh_vertices
         id_number = bc.id