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Selecting Fluid>Mesh>"Use Speed Vectors" deletes all existing cache without warning
Closed, ResolvedPublic

Description

System Information
Operating system: Ubuntu 18.04
Graphics card: Irrelevant

Blender Version
Broken: 2.83 ff7a30d92884 18 May 2020

Short description of error

In the "modular cache" fluid workflow, to a certain extent it is expected that (1) fluid, (2) mesh, (3) particles can be set up and baked at separate stages.

However, *Fluid > Mesh > Use speed vectors* probably requires a special kind of "fluid" cache with speed vectors enabled. Therefore, clicking on "Use Speed Vectors" immediately, and without a warning, deletes the baked cache. This potentially loses hours of compute work.

Exact steps for others to reproduce the error

  • Open this basic setup

  • Bake the Data, then select "Use Speed Vectors". The baked data is gone.

Possible solutions

Assuming that a new bake of the data is actually needed in order to have speed vectors available, there are two possible solutions and possibly others:

  1. When the user selects "Use Speed Vectors", instead of deleting the cache, just disable ("grey out") the Bake Mesh button and add a message under it that says _"⚠️ Baking the Mesh with speed vectors requires a fresh Data bake"_. This way the user will decide whether they want to free and re-bake, or just give up speed vectors.
  1. (my preferred option) Add a "generate speed vectors" in the Data Bake section, with a tooltip saying "Needed for mesh motion blur" or similar. If the user hasn't generated the speed vectors, the Mesh>"Use speed vectors" checkbox will be disabled, with a tooltip explaining why.
  1. (this sounds like a temporary solution though) Add a much more aggressive message to the current tooltip: "WARNING: if you check this box, your data bake will be lost"