Split bmesh by material

Coding Python Support
1

I’ve got a bmesh that I’ve created from an object and I need to export it into mesh buffers seperated by material for my engine. Is there any way to split a bmesh by material like using P in edit mode does? I’ve searched around, but I could never find any good method of doing it. Does anyone know of a way to do this?

2

3DModelerMan,
Go to edit mode and select all faces and clic P separate ->by materials
simply! Return in Object mode and you have x nber objects of your original by material!
Bye bye and good blend.
Spirou4D

Edit: But what do you want to say Bmesh? NURBs?
Blender use bmesh now on all faces and it’s not different as a quad face!

3

No, I created a bmesh from an object using the from_object method of the Python API so that I could apply all modifiers and triangulate it. I want to split the temporary mesh by material.

4

I repeat my question: What is “mesh buffers” and what do you want to say “Bmesh” for you, please?

5

I’ll just post my code so it’s a little easier to get my question across. I get a bmesh from the object I’m trying to save, but I want to be able to split it up by material.

def saveMeshComponent(context, props, obj):
#Create temporary mesh with modifiers applied
bm = bmesh.new();
bm.from_object(obj, bpy.context.scene, deform=False, render=True);

bmesh.ops.triangulate(bm, faces=bm.faces);

#I'd like to be able to seperate my mesh by material here...

bm.free();
del bm;

#Create mesh component
meshComp = {
	"Range": float(obj.data.distance),
	"Cast Shadows": obj.data.shadow_method != 'NOSHADOW'
};

return meshComp;
6

You must separate your bmesh after your method “saveMeshComponent()” and apply modifiers, use the result and apply:



def execute(self, context):        if bpy.context.mode != 'EDIT':            #if not in edit mode
            bpy.ops.object.editmode_toggle()      #enters in edit mode
            bpy.ops.mesh.separate(type='MATERIAL')   #separate it by material parts
            bpy.ops.object.editmode_toggle()      #exit edit mode
        else :                                    #else
            bpy.ops.mesh.separate(type='MATERIAL')   #separate it by material parts
        
        self.report({'INFO'}, "Mesh separated")
        return{'FINISHED'}

-> “BMesh is a NON-MANIFOLD boundary representation.”
you must go out this non-manifold structure for separate them.

7

Is there any way to access the objects created by the separate operator? I want to run the operator on a temporary duplicate object, and then save the resulting split up objects and delete them when I’m done. The documentation for ops says it returns a set with the return code, but it doesn’t have anything about the accessing operator’s results.

8

Why temporary duplicate object?

>>>" it returns a set with the return code"
Open Notepad+ and go to “search and replace” and make a search in directory with “mesh.separate(type=‘MATERIAL’)” in your extern or normal/contrib add-ons and you will find all addons that use this operator. You can understand his behavior.

Prefer the normal/contrib add-ons because the coder of Blender are more accurate.

  • “meshComp = {
    “Range”: float(obj.data.distance),
    “Cast Shadows”: obj.data.shadow_method != ‘NOSHADOW’
    };”

It return a distance range(a float number) and a bool value for cast shadow AND the mesh.

9

make sure you clear object selection, then make the object you want to separate material active and selected.

after the operator call, all new objects will be selected (bpy.context.selected_objects)

10

Function bmesh.ops.split is not usable yet.
Following method maybe not efficient. It makes whole bmesh copy in material loop, then remove faces with other materials.

def split_bmesh_by_material(ob):
    # Get mesh of target object
    me = ob.data
    print ('Count of mesh faces: ', len(me.polygons))
    # we want to know how many materials assigned to this mesh  
    mat_count = len(me.materials)
    
    #Create multiple temporary bmesh with modifiers applied
    bms = []
    
    # split bms by materials
    for mat_i in range (0, mat_count):  
      bms.append(bmesh.new())
      bms[mat_i].from_object(ob, bpy.context.scene, deform=False, render=True)
      # remove faces with other materials
      for f in bms[mat_i].faces:
        if f.material_index != mat_i:
          bms[mat_i].faces.remove(f)
      
    for bm_i in range (0, mat_count):
      print ('bm ', bm_i, 'count of faces: ', len(bms[bm_i].faces))
      bmesh.ops.triangulate(bms[bm_i], faces=bms[bm_i].faces);
      print ('bm ', bm_i, 'count of triangulated faces: ', len(bms[bm_i].faces))

    # maybe do bms exporting here ...
    
    # at the end, release the memory
    for bm in bms:
      bm.free();
      
    return