[Quick question]How to select a group cells in a mesh?

[ZiguoAtGitHub]

Hi Marcomusy and other masters
I create a mesh with Mesh([verts,cells]], which includes a large number ploygons. How can I select a group of ploygons and hide them?
Thank you all!

[marcomusy]

Hi,
What do you mean by "select"? You need to be more specific.

[ZiguoAtGitHub]

I look in vedo's doc. maybe the meaning of "select" is same as "extract" ,:)

[ZiguoAtGitHub]

Dear Marco,@marcomusy
I should explain my problem more clearly with the following codes:

"""Manually build a mesh from points and faces"""
from vedo import Mesh, show

verts = [(50,50,50), (70,40,50), (50,40,80), (80,70,50)]
faces = [(0,1,2), (2,1,3), (1,0,3)]
''' (the first triangle face is formed by vertex 0, 1 and 2)
Build the polygonal Mesh object:'''
mesh = Mesh([verts, faces])
mesh.backcolor('violet').linecolor('tomato').linewidth(2)
labs = mesh.labels('id').c('black')
#-----------------------------------------------------

My problem is: How to show the first triangle only, but keep the codes above the dashed line UNCHANGED

show(mesh, labs, __doc__, viewup='z', axes=1).close()

Please let me know if you can not get my point. Thank you again.

BTW:
If I create each mesh for every single triangle, I can specify the first mesh on and off for the other two.
But for a large number triangles, the speed for plot will be decreased dramatically. I already tried.

[marcomusy]

PS: note that if you have defined some color mapping you can retrieve the current RGBA values and mask the faces you like by setting to zero the fourth column, eg:

from vedo import Mesh, show

verts = [(50,50,50), (70,40,50), (50,40,80), (80,70,50)]
faces = [(0,1,2), (2,1,3), (1,0,3)]

mesh = Mesh([verts, faces])
mesh.cmap("jet", mesh.cell_centers()[:,2], on="cells")
#-----------------------------------------------------

print(mesh.retrieve_rgb(on="cells", alpha=True))

# mesh.cell_individual_colors([...])

show(mesh, axes=1)

[ZiguoAtGitHub]

Hi Marco,
First of all, thank you for your kindly reply of every question!

I am not good at asking questions, especially on web. Sorry about that.

In fact, I want to control every individual cell in a mesh, its color, its visibility and etc.
The lazy way I had tried is creating independent mesh for every triangle. It works well for very smaller numbers of triangles. When the number of triangles increases to over 10k, the plotting speed will be decreased severely as I noted previously.

Another doable method is calling plt.clear(), then creating new meshes and plot them every time. It also works.
But there is one little unpleasant problem: when I change to plot new meshes the plot window will be blank for several seconds.
Is this the best way? Would you like to give some hints for me?

I have no idea about whether vedo can provides more flexibility on individual cell in a mesh or not.
If not, I am very looking forward for that.

Thank you again!
🙂

[ZiguoAtGitHub]

Dear Marco,
Please forget the above question about the second method. I improve the codes the problem is gone.
🙂

[marcomusy]

Note that function will change name in the next release from
mesh.retrieve_rgb(on="cells", alpha=True)
to
mesh.get_rgba("cells")

[ZiguoAtGitHub]

OK. Thanks.