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Hi @bjlotus, hi @Cairyn, there is one problem with your normals calculation. You calculate just a vertex normal in the polygon and then declare it to be the polygon normal 😉 (your variable "cross"), i.e., you assume all your polygons to be coplanar. With today's high density meshes you can probably get away with that to a certain degree, but it would not hurt to actually calculate the mean vertex normal of a polygon, a.k.a., the polygon normal to have a precise result. The problem with your "flattening" is that it is not one. Unless I have overread something here in the thread, the missing keyword would be a point-plane projection. You just translate all selected points by a fixed amount, which was if I understood that correctly only a work in progress, but obviously won't work. Things could also be written a bit more tidely and compact in a pythonic fashion, but that has very little impact on the performance and is mostly me being nitpicky 😉 I did attach a version of how I would do this at the end (there are of course many ways to do this, but maybe it will help you). Cheers, Ferdinand """'Flattens' the active polygon selection of a PolygonObject. Projects the points which are part of the active polygon selection into the mean plane of the polygon selection. """ import c4d def GetMean(collection): """Returns the mean value of collection. In Python 3.4+ we could also use statistics.mean() instead. Args: collection (iterable): An iterable of types that support addition, whose product supports multiplication. Returns: any: The mean value of collection. """ return sum(collection) * (1. / len(collection)) def GetPolygonNormal(cpoly, points): """Returns the mean of all vertex normals of a polygon. You could also use PolygonObject.CreatePhongNormals, in case you expect to always have a phong tag present and want to respect phong breaks. Args: cpoly (c4d.Cpolygon): A polygon. points (list[c4d.vector]): All the points of the object. Returns: c4d.Vector: The polygon normal. """ # The points in question. a, b, c, d = (points[cpoly.a], points[cpoly.b], points[cpoly.c], points[cpoly.d]) points = [a, b, c] if c == d else [a, b, c, d] step = len(points) - 1 # We now could do some mathematical gymnastics to figure out just two # vertices we want to use to compute the normal of the two triangles in # the quad. But this would not only be harder to read, but also most # likely slower. So we are going to be 'lazy' and just compute all vertex # normals in the polygon and then compute the mean value for them. normals = [] for i in range(step + 1): o = points[i - 1] if i > 0 else points[step] p = points[i] q = points[i + 1] if i < step else points[0] # The modulo operator is the cross product. normals.append(((p - q)) % (p - o)) # Return the normalized (with the inversion operator) mean of them. return ~GetMean(normals) def ProjectOnPlane(p, q, normal): """Projects p into the plane defined by q and normal. Args: p (c4d.Vector): The point to project. q (c4d.Vector): A point in the plane. normal (c4d.Vector): The normal of the plane (expected to be a unit vector). Returns: c4d.Vector: The projected point. """ # The distance from p to the plane. distance = (p - q) * normal # Return p minus that distance. return p - normal * distance def FlattenPolygonSelection(node): """'Flattens' the active polygon selection of a PolygonObject. Projects the points which are part of the active polygon selection into the mean plane of the polygon selection. Args: node (c4d.PolygonObject): The polygon node. Returns: bool: If the operation has been carried out or not. Raises: TypeError: When node is not a c4d.PolygonObject. """ if not isinstance(op, c4d.PolygonObject): raise TypeError("Expected a PolygonObject for 'node'.") # Get the point, polygons and polygon selection of the node. points = node.GetAllPoints() polygons = node.GetAllPolygons() polygonCount = len(polygons) baseSelect = node.GetPolygonS() # This is a list of booleans, e.g., for a PolygonObject with three # polygons and the first and third polygon being selected, it would be # [True, False, True]. polygonSelection = baseSelect.GetAll(polygonCount) # The selected polygons and the points which are part of these polygons. selectedPolygonIds = [i for i, v in enumerate(polygonSelection) if v] selectedPolygons = [polygons[i] for i in selectedPolygonIds] selectedPointIds = list({p for cpoly in selectedPolygons for p in [cpoly.a, cpoly.b, cpoly.c, cpoly.d]}) selectedPoints = [points[i] for i in selectedPointIds] # There is nothing to do for us here. if not polygonCount or not selectedPolygons: return False # The polygon normals, the mean normal and the mean point. The mean point # and the mean normal define the plane we have to project into. Your # image implied picking the bottom plane of the bounding box of the # selected vertices as the origin of the plane, you would have to do that # yourself. Not that hard to do, but I wanted to keep things short ;) polygonNormals = [GetPolygonNormal(polygons[pid], points) for pid in selectedPolygonIds] meanNormal = ~GetMean(polygonNormals) meanPoint = GetMean(selectedPoints) # Project all the selected points. for pid in selectedPointIds: points[pid] = ProjectOnPlane(points[pid], meanPoint, meanNormal) # Create an undo, write the points back into the polygon node and tell # it that we did modify it. doc.StartUndo() doc.AddUndo(c4d.UNDOTYPE_CHANGE, node) node.SetAllPoints(points) doc.EndUndo() node.Message(c4d.MSG_UPDATE) # Things went without any major hiccups :) return True def main(): """Entry point. """ if FlattenPolygonSelection(op): c4d.EventAdd() if __name__ == '__main__': main()

Hi @bjlotus, This was not me be pedantic about terminology and you are computing the mean and the normals. I was just pointing out that you were just computing the normal for one of the planes in a polygon - unless I am overlooking something here. But for quads there are two, one for each triangle in the quad. Below is an illustration of a quad which I did manually triangulate for illustration purposes. You can see the vertex normals in white (which are each equal to the normal of the triangle/plane the lie in). And two plane normals in black, one for each triangle. The actual polygon normal is then the arithmetic mean of both plane normals. So when you just pick one vertex in a quad to calculate the polygon normal, i.e., simply say one of the white normals is the polygon normal, then you assume that both tris of the quad lie in the same plane, i.e., that the quad is coplanar. Which of course can happen, but there is no guarantee. Quads are today usually quite close to being coplanar (and not that comically deformed as my example), but you will still introduce a little bit of imprecision by assuming all quads to be coplanar. Cheers, Ferdinand

Thanks @zipit for posting solution. Love to see part of code very well described how all that things go 🙂 ...

Hi @Cairyn, hm, I did not want to imply otherwise. I was just polite and said hi to everyone before waltzing in here 😉. Assuming my "hi @Cairyn" was the cause for that misunderstanding. Cheers, Ferdinand

😁 Indeed. Zbrush is the one 3d app that I have never been able to get along with. But I do appreciate its functionality.