Modifier: Mirror learns to bisect on plane

D3966 by @kioku w/ edits.

This adds bisect and flip options to mirror modifier.

1 files changed, 94 insertions, 6 deletions

diff --git a/source/blender/modifiers/intern/MOD_mirror.c b/source/blender/modifiers/intern/MOD_mirror.c
index d4e02a437d7..df08122aebf 100644
--- a/source/blender/modifiers/intern/MOD_mirror.c
+++ b/source/blender/modifiers/intern/MOD_mirror.c
@@ -45,6 +45,9 @@
 #include "BKE_modifier.h"
 #include "BKE_deform.h"
 
+#include "bmesh.h"
+#include "bmesh_tools.h"
+
 #include "MEM_guardedalloc.h"
 
 #include "DEG_depsgraph_build.h"
@@ -78,21 +81,90 @@ static void updateDepsgraph(ModifierData *md, const ModifierUpdateDepsgraphConte
 	DEG_add_object_relation(ctx->node, ctx->object, DEG_OB_COMP_TRANSFORM, "Mirror Modifier");
 }
 
-static Mesh *doMirrorOnAxis(
+static Mesh *doBiscetOnMirrorPlane(
         MirrorModifierData *mmd,
         Object *ob,
         const Mesh *mesh,
-        int axis)
+        int axis,
+        float mirrormat[4][4])
+{
+	bool do_flip_axis = (
+	        (axis == 0 && mmd->flag & MOD_MIR_FLIP_AXIS_X) ||
+	        (axis == 1 && mmd->flag & MOD_MIR_FLIP_AXIS_Y) ||
+	        (axis == 2 && mmd->flag & MOD_MIR_FLIP_AXIS_Z));
+
+	const float bisect_distance = 0.001;
+
+	Mesh *result;
+	BMesh *bm;
+	BMIter viter;
+	BMVert *v, *v_next;
+
+	bm = BKE_mesh_to_bmesh_ex(
+		mesh,
+		&(struct BMeshCreateParams){0},
+		&(struct BMeshFromMeshParams){
+			.calc_face_normal = true,
+			.cd_mask_extra = CD_MASK_ORIGINDEX,
+		});
+
+	/* prepare data for bisecting */
+	float plane[4];
+	float plane_co[3] = {0, 0, 0};
+	float plane_no[3];
+	copy_v3_v3(plane_no, mirrormat[axis]);
+
+	if (mmd->mirror_ob) {
+		float tmp[4][4];
+		invert_m4_m4(tmp, ob->obmat);
+		mul_m4_m4m4(tmp, tmp, mmd->mirror_ob->obmat);
+
+		copy_v3_v3(plane_no, tmp[axis]);
+		copy_v3_v3(plane_co, tmp[3]);
+	}
+
+	plane_from_point_normal_v3(plane, plane_co, plane_no);
+
+	BM_mesh_bisect_plane(bm, plane, false, false, 0, 0, bisect_distance);
+
+	/* Plane definitions for vert killing. */
+	float plane_offset[4];
+	copy_v3_v3(plane_offset, plane);
+	plane_offset[3] = plane[3] - bisect_distance;
+
+	if (do_flip_axis) {
+		negate_v3(plane_offset);
+	}
+
+	/* Delete verts across the mirror plane. */
+	BM_ITER_MESH_MUTABLE(v, v_next, &viter, bm, BM_VERTS_OF_MESH) {
+		if (plane_point_side_v3(plane_offset, v->co) > 0.0f) {
+			BM_vert_kill(bm, v);
+		}
+	}
+
+	result = BKE_mesh_from_bmesh_for_eval_nomain(bm, 0);
+	BM_mesh_free(bm);
+
+	return result;
+}
+
+static Mesh *doMirrorOnAxis(
+	MirrorModifierData *mmd,
+	Object *ob,
+	const Mesh *mesh,
+	int axis)
 {
 	const float tolerance_sq = mmd->tolerance * mmd->tolerance;
 	const bool do_vtargetmap = (mmd->flag & MOD_MIR_NO_MERGE) == 0;
 	int tot_vtargetmap = 0;  /* total merge vertices */
 
+	const bool do_bisect = (
+	        (axis == 0 && mmd->flag & MOD_MIR_BISECT_AXIS_X) ||
+	        (axis == 1 && mmd->flag & MOD_MIR_BISECT_AXIS_Y) ||
+	        (axis == 2 && mmd->flag & MOD_MIR_BISECT_AXIS_Z));
+
 	Mesh *result;
-	const int maxVerts = mesh->totvert;
-	const int maxEdges = mesh->totedge;
-	const int maxLoops = mesh->totloop;
-	const int maxPolys = mesh->totpoly;
 	MVert *mv, *mv_prev;
 	MEdge *me;
 	MLoop *ml;
@@ -125,6 +197,18 @@ static Mesh *doMirrorOnAxis(
 		mul_m4_m4m4(mtx, itmp, mtx);
 	}
 
+
+	Mesh *mesh_bisect = NULL;
+	if (do_bisect) {
+		mesh_bisect = doBiscetOnMirrorPlane(mmd, ob, mesh, axis, mtx);
+		mesh = mesh_bisect;
+	}
+
+	const int maxVerts = mesh->totvert;
+	const int maxEdges = mesh->totedge;
+	const int maxLoops = mesh->totloop;
+	const int maxPolys = mesh->totpoly;
+
 	result = BKE_mesh_new_nomain_from_template(
 	        mesh, maxVerts * 2, maxEdges * 2, 0, maxLoops * 2, maxPolys * 2);
 
@@ -290,6 +374,10 @@ static Mesh *doMirrorOnAxis(
 		MEM_freeN(vtargetmap);
 	}
 
+	if (mesh_bisect != NULL) {
+		BKE_id_free(NULL, mesh_bisect);
+	}
+
 	return result;
 }