Assign face material in loop

Coding Python Support
1


I have a small script I’ve written. It creates a grid of faces, all part of a single object. What I want to do is assign a material to certain faces. I’m more interested in the viewport color, and I don’t care if it’s cycles or BI. Basically where I print the color, I need some code that looks somthing like: face.assignmat(’#ff0000’)


import bpy

def deleteOldObject():
    scene = bpy.context.scene
    for ob in scene.objects:
        if ob.type == 'MESH' and (ob.name.startswith("Cube") or ob.name.startswith("Plane")):
            ob.select = True
        else: 
            ob.select = False

    bpy.ops.object.delete()    


deleteOldObject()

xmax = 3
ymax = 7
cubescale = .2
scale = .2

verts=[]
faces=[]
facecount = 0
facecolor =[]
for x in range(0,xmax):
    for y in range(0,ymax):
        verts.append((scale + x , scale+y, 0))  
        verts.append((scale+x, -scale+y, 0))  
        verts.append((-scale+x, -scale+y, 0))  
        verts.append((-scale+x, scale+y, 0)) 
        facecount = facecount + 1
        if (x==2 and y==3):
            facecolor.append('red')
        else:
            facecolor.append('blue') 
            
for findex in range(0,facecount):
    f = ( ((findex*4)) , ((findex*4)+1) , ((findex*4)+2) , ((findex*4)+3)  )
    print(facecolor[findex])  #I WANT TO ACTUALLY CHANGE THE FACE COLOR/MATERIAL
    faces.append(f)
        
  
mesh_data = bpy.data.meshes.new("cube_mesh_data")  
mesh_data.from_pydata(verts, [], faces)  
mesh_data.update() # (calc_edges=True) not needed here  
  
cube_object = bpy.data.objects.new("Cube_Object", mesh_data)  
  
scene = bpy.context.scene    
scene.objects.link(cube_object)    
cube_object.select = True
2

If you already have the materials in the objects material slots, all you have to do is assign the faces material_index to the material you want.


obj.data.polygons[0].material_index = 2 #with obj as your object, change face[0] material to third material in object.
3

Ok, thank you. But the problem is the object is created each time the script the script runs. It has no materials.

4

Where will you have the materials then, sitting in memory?

5

I want to either create the material on the fly and then assign them to the newly created faces, or possibly borrow them from a separate object which I can keep in the scene created manually. Are you saying you can’t create material slots programmatically?

6

Yes, you can. That’s why I was asking. So which one do you want to do?

7

It doesn’t really matter. I guess I’d like to know how to create it completely with code, so something like
mat = bpy.foo.bar.mat("#ff00000,“myredmat”,"")
f.assignmat(mat)
faces.append(f)

As I mentioned before, I am much more interested in changing the viewport color.

8 

redMat = bpy.data.materials.new('redMat') #creates new material
redmat.diffuse_color = 255,0,0 changes color to red
obj.data.materials.append(redMat) # adds material to object
9

Ok, thank you very much @cmomoney. It works now. It looks a little ugly, because at the time the vertices and faces are being defined, there exists no object, so I had to create the object, add the materials, and then loop through the faces again and assign them. I appreciate your help. Here is the working code.


import bpy

def deleteOldObject():
    scene = bpy.context.scene
    for ob in scene.objects:
        if ob.type == 'MESH' and (ob.name.startswith("Cube") or ob.name.startswith("Plane")):
            ob.select = True
        else: 
            ob.select = False

    bpy.ops.object.delete()    


deleteOldObject()

xmax = 3
ymax = 7
scale = .2

verts=[]
faces=[]
facecount = 0
facecolor =[]
for x in range(0,xmax):
    for y in range(0,ymax):
        verts.append((scale + x , scale+y, 0))  
        verts.append((scale+x, -scale+y, 0))  
        verts.append((-scale+x, -scale+y, 0))  
        verts.append((-scale+x, scale+y, 0)) 
        if (x==2 and y==3):
            facecolor.append(1)  #0 IS THE INDEX OF RED
        else:
            facecolor.append(0)  #1 IS THE INDEX OF BLUE
        facecount = facecount + 1
            
for findex in range(0,facecount):
    f = ( ((findex*4)) , ((findex*4)+1) , ((findex*4)+2) , ((findex*4)+3)  )
    print(facecolor[findex])  #I WANT TO ACTUALLY CHANGE THE FACE COLOR/MATERIAL
    faces.append(f)
         
mesh_data = bpy.data.meshes.new("cube_mesh_data")  
mesh_data.from_pydata(verts, [], faces)  
mesh_data.update() # (calc_edges=True) not needed here  
  
cube_object = bpy.data.objects.new("Cube_Object", mesh_data)  
  
scene = bpy.context.scene    
scene.objects.link(cube_object)    
cube_object.select = True   

redMat = bpy.data.materials.new('redMat') #creates new material
redMat.diffuse_color = (255,0,0) #changes color to red
blueMat = bpy.data.materials.new('blueMat') #creates new material
blueMat.diffuse_color = (0,0,255) 
cube_object.data.materials.append(blueMat) 
cube_object.data.materials.append(redMat) 

for f in cube_object.data.polygons:
    f.material_index = facecolor[f.index]