How to make disintegration or dissolve effect from center of the object with texture or geometry nodes?

Question

I need to make dissolving effect on simple plane, from the object center. I tried to make it with material shader by using gradient map but in my case it doesn't work as I need because the effect seems like clockwise appearance. Also used a Build Modifier but can't control the started point of it, in my case i need that dissolve effect starts from center not from the sides or up/down. Think it could be done with Geometry Nodes...

Maybe someone know the solution, thanks in advance! I provide the blend file

Answer 1

Since you mention the Build modifier and the problem being the order of this modifier is not satisfying, you should be happy to learn the order of the modifier is the indices of the faces, which can be easily sorted by their distance from the 3D cursor:

(make sure you're in 3 Face Selection Mode and your faces are selected)

Now your build modifier (in reversed order) works as expected:

If you're unhappy with how easy it was, you can apply some additional tricks…

Advanced sorting using Python

(run in Edit Mode)

import bmesh
from bpy import context as C
from math import atan2

me = C.object.data
bm = bmesh.from_edit_mesh(C.object.data)
coords = [f.calc_center_median().yx for f in bm.faces]
distances_to_center = (co.length for co in coords)
angles = (atan2(*co) for co in coords)
combined = zip(angles, distances_to_center, bm.faces[:])
sorted_by_angle_and_distance = sorted(combined, key=lambda x:x[0]+x[1]*20)
for i, (angle, _, face) in enumerate(sorted_by_angle_and_distance):
    face.index = i
bm.faces.sort()
bmesh.update_edit_mesh(me)

Varying animation speed

Since the Build modifier has a constant speed in faces per frame, as it approaches the center of the circle, it seems to speed up, because there's just less faces per each ring as you get closer to the center (at least if your topology is a grid, rather than something like this). Consider setting the animation length to the number of faces, and the starting frame to a custom driver - for an explanation how to do so see this thread:

Build animation modifier build up and then reverse

Answer 2

Since you use geometry-nodes here, I'll try to answer this question with Geometry Nodes, of course:

Just use the nodes Scene Time and Map Range to define the time range and effect ratio. From Min and From Max corresponds to the values you used for the build modifier. The values for To Min and To Max define the area of effect or the distance of an object starting from the center.

If you reverse these values in the mapping, the effect also reverses in the opposite direction.

As soon as the distance of a face is below this resulting value, it may remain, and if not, it should be deleted.