How can I select only the front facing polygons of an object?

Question

I want to select the front face, but I don’t want to select the back face

bpy.ops.view3d.select_box(xmin=0,xmax=area.width,ymin=0,ymax=area.height,wait_for_input=False,mode='SET')

actual：

hope：

How to ignore the back? The backside culling is useless.

Answer 1

This will select the front-facing faces of the selected object.

Conditions :

• You must be in OBJECT mode.
• Your object must be a MESH object.
• You workspace must contain at least a 3D viewport editor.

You'll have to learn a bit about the dot product : https://en.wikipedia.org/wiki/Dot_product

import bpy
import mathutils

mesh = bpy.context.object.data  # Retrieve the mesh
normals = [p.normal for p in mesh.polygons]  # Compute polygon normals

# Compute the view direction
up = mathutils.Vector((0.0, 0.0, 1.0))
view3d_area = next(a for a in bpy.context.screen.areas if a.ui_type == 'VIEW_3D')
trans_world = (view3d_area.spaces.active.region_3d.view_matrix.inverted()).to_3x3() @ up
trans_world.normalize()

# Unselect the mesh elements
for v in mesh.vertices:
    v.select = False
for e in mesh.edges:
    e.select = False
    
for i, normal in enumerate(normals):
    # Select the front facing faces
    mesh.polygons[i].select = trans_world.dot(normal) >= 0

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