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Incorrect modifier stack evaluation after Decimate-Planar modifier.
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System Information
Win7 / GTX460

Blender Version
Broken: blender-2.77.0-git.7ac126e-AMD64

Short description of error
Modifiers used after Decimate with Planar option behave wrong. Seems like part of decimation work after those modifiers which should not happen. Using Smooth after Decimate should only deform mesh but topology changes randomly.

Exact steps for others to reproduce the error

Modify Repeat value in Smooth modifier. Topology of mesh changes. Note that same value can result completely different topology.
Modify Factor value in Cast modifier. Topology changes despite modifier is disabled.
Turn of Smooth modifier and enable Cast modifier.
Change Factor value. Topology is jiggling.



Event Timeline

Bartosz Moniewski (monio) updated the task description. (Show Details)
Bartosz Moniewski (monio) raised the priority of this task from to Needs Triage by Developer.
Bartosz Moniewski (monio) set Type to Bug.

Just in case: I have applied Boolean modifier in the provided file and then tried to change the values of Smooth and Cast modifiers and noticed that their topology doesn't jiggle like it does with Boolean modifier in the stack. Don't know if that will help with anything but still.

Didn't tested that. Thanks.
On 2.76 jiggling still happen but only on boolean intersection.
Both in 2.76 and current master Decimation set to Collapse works fine, topology stays intact.

Boolean modifier (Carve) doesn't give us back *ordered* results.
That means every refresh, the geometry may be completely re-arranged.

Whats happening here is the decimate method has many edges which have the same cost of removing, so the boolean modifier causes unpredictable results.

We have had similar reports before, and since this isn't something we can resolve easily (and may replace carve anyway),
closing this report.