Yamyam: 1版をインポートしました

2018-06-28T21:16:06Z

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2016年3月5日 (土) 19:41にwiki>TheBusyTypistによる

2016-03-05T19:41:31Z

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= Overview =

Name: Ounan Ding

E-mail: ounanding@gmail.com

IRC: TheBusyTypist

GitHub: https://github.com/thebusytypist

Blog: http://blender.linearconstraints.net

There is a PDF version of this proposal, which has better typesetting:
https://github.com/thebusytypist/gsoc-2016-doc/raw/master/proposals/mesh-undo-memory/mesh-undo-memory.pdf

= Synopsis =

I propose to optimize the memory usage of mesh undo.

= Benefits to Blender =

This project will reduce the memory usage and makes editing on detailed meshes
easier.

Moreover, I will also take this chance to write or
to improve the documentation on Blender operator system
and operation history mechanism.

= Deliverables =

This project allows artists edit larger mesh object
before hitting the memory limitation.
The modification on the source code will be transparent
to the artists.

= Project Details =

In this section I will first review the current implementation of
mesh undo mechanism, and discuss the potential issues of it.
After that I propose several optimization ideas and estimate
a preliminary project schedule.

== Review of Current Implementation ==

In Blender, all operations on mesh object are encapsulated as
Blender Operators.
And whenever an Operator is successfully executed,
a snapshot of the current state will be captured and stored
into the operation history.

I have a blog post[http://blender.linearconstraints.net/2016/02/28/notes-on-undo.html] on the details of the undo mechanism.
Generally speaking,
the operation history is stored in a list ''undobase''.
And current state, which is a ''UndoElem'' structure,
is pushed into the operation history.

''UndoElem'' contains several function pointers to be filled
by specific object types.
These functions handles how current state is retrieved, duplicated
to the operation history,
and how it is restored and release on an undo command given by user.
In fact, this is the polymorphism in C style.

For mesh data, the override functions are provided in
''editmesh_utils.c''.
The current strategy is
that the whole mesh data get duplicated and restored on the undo command,
which requires a lot of memory for a very detailed mesh object.

== Design ==

According to our analysis on the current implementation,
we can see that
the general optimization direction is to avoid doing the complete duplication.

Moreover, each Operator itself has the best knowledge of how will it modify the
mesh data
and how will the result mesh data be different than the input one.
So we want to allow programmer customize the undo strategy
for different Operators
in order to achieve the optimal memory usage.

Concretely, I propose following design:

* The set of function pointers in ''UndoElem'' will be move to ''wmOperatorType'', where the programmer defines a ''wmOperator''. Thus the programmer can provide a custom undo strategy for specific Operator. We call this set of functions as "undo functions".

* We pass the undo functions through ''ED_undo_push'', to ''undo_push_mesh'', where the ''UndoElem'' gets assembled. Thus the custom undo strategy can be dispatched dynamically.

* We also have a code path that when no custom undo strategy is provided by an Operator, we fall back to the default behavior: make a complete replica and restore the memory on undo command.

After we refactor the Operator/undo system,
we can consider the specific undo strategies now.

For Operators which exhibit locality in their behavior,
we can store the delta data only.
This will reduce the memory usage dramatically.

= Project Schedule =

In the first two weeks I will refactor on the Operator/undo system,
which is proposed above.
In this stage only default undo strategy is used.
We will perform tests to ensure nothing is broken in the refactoring.
The memory usage will also be recorded as the baseline for later benchmarking.

After that I start to implement the specific undo strategies for individual
Operators.
We also propose new strategies while we are proceeding.
We will iterate rapidly in this second stage.

= Bio =

Currently I am a master student from University of California, Riverside.
In my previous job
I was in charge of a particle system editor with fully undo/redo support.
I run a blog[http://http://blender.linearconstraints.net]
on Blender development. I have some articles about Blender operator
and operation history system there.

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利用者:TheBusyTypist/GSoC2016-Mesh-Undo-Memory - 版の履歴

Yamyam: 1版 をインポートしました

2016年3月5日 (土) 19:41にwiki>TheBusyTypistによる

Yamyam: 1版をインポートしました