Lightmap unwrap improvements - performance improvement #113720

Sebastian Witt · 2023-10-14T14:47:29+02:00

Sebastian Witt commented

2023-10-14 14:47:29 +02:00

This is the second part of two improvements i want to propose to the lightmap unwrap functionality.
The first part can be found here: #113716

In this i tried to improve the performance of triangle unwrapping. On meshes with high triangle counts this was very slow since the original algorithm iterates over all triangles and then calculates the edge length distance to each other triangle in every iteration resulting in ~n^2 complexity.

The proposed solution replaces this search by representing the 3 edge lengths of each triangle as 3d points and searching with a kd-tree.

On a mesh with ~20k Tris the old method runs in 40s while the new method takes 0.23s with a difference of <0.001%.

Testing:
To test the functionality it is not enough to compare the exact result of the old method with the new method since equal triangles might get mapped differently since the kd-tree doesn't reproduce the same order as with the iterative method.

The measures i took is the area of the resulting uvmap should be close to the original method and should only contain overlapping elements if the original method also produces an overlapping result. (There might be another bug related to tris)

My testing script is attached. It loads the original "uvcalc_lightmap.py" and a new "uvcalc_lightmap_kd.py" and runs the unwrap function on the currently selected object.

Sidenote:
To put the importance of this into perspective, the resulting lightmaps of high triangle count meshes is rarely usable since each tri is uvmapped as an island thus takes away a lot of space with added margins.
Regardless of that i think blender shouldn't freeze for ages if i unwrap such a mesh without thinking whether it will be useful.

Any feedback, tips, general thoughts or possible improvements to style etc. is very welcome!

This is the second part of two improvements i want to propose to the lightmap unwrap functionality. The first part can be found here: #113716 In this i tried to improve the performance of triangle unwrapping. On meshes with high triangle counts this was very slow since the original algorithm iterates over all triangles and then calculates the edge length distance to each other triangle in every iteration resulting in ~n^2 complexity. The proposed solution replaces this search by representing the 3 edge lengths of each triangle as 3d points and searching with a kd-tree. On a mesh with ~20k Tris the old method runs in 40s while the new method takes 0.23s with a difference of <0.001%. Testing: To test the functionality it is not enough to compare the exact result of the old method with the new method since equal triangles might get mapped differently since the kd-tree doesn't reproduce the same order as with the iterative method. The measures i took is the area of the resulting uvmap should be close to the original method and should only contain overlapping elements if the original method also produces an overlapping result. (There might be another bug related to tris) My testing script is attached. It loads the original "uvcalc_lightmap.py" and a new "uvcalc_lightmap_kd.py" and runs the unwrap function on the currently selected object. Sidenote: To put the importance of this into perspective, the resulting lightmaps of high triangle count meshes is rarely usable since each tri is uvmapped as an island thus takes away a lot of space with added margins. Regardless of that i think blender shouldn't freeze for ages if i unwrap such a mesh without thinking whether it will be useful. _Any feedback, tips, general thoughts or possible improvements to style etc. is very welcome!_

uvunwrap_test_objs.blend

21 MiB

uv_unwrap_test.py

2.9 KiB

❤️ 2 🚀 3

Sebastian Witt added 1 commit 2023-10-14 14:47:41 +02:00

3b10904975 improved lightmap pack performance

Sebastian Witt referenced this pull request

2023-10-14 15:00:14 +02:00

Lightmap unwrap improvements - prevent division by zero #113716

Sebastian Witt requested review from Campbell Barton 2023-10-17 16:50:41 +02:00

Iliya Katushenock added this to the Modeling project 2023-11-30 17:01:32 +01:00

Iliya Katushenock added the

 @ -320,1 +345,3 @@
                 pretty_faces.append(prettyface((tri1, tri_lengths.pop(best_tri_index))))
                 if i % 100 == 0:
                     wm.progress_update(i)
                     print(f"Unwrap progress {int((100 * pairs_added / num_tri_pairs))}%")

 @ -311,2 +333,2 @@
                 best_tri_index = -1
                 best_tri_diff = 100000000.0
                 # look in threshold vicinity to add all similar/equal tris in one go
                 if False and dist < tri_equality_threshold:

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Lightmap unwrap improvements - performance improvement #113720

Pull request closed