[Soc-2017-dev] Weekly Report #02 - Silhouette Operator

[Sebastian Witt]

**

*Week twois over, time for a small summary on the Silhouette Operator:*

*

I designated this week to get the base done. A rough operator skeleton 
is now in place, custom draw-calls for the UI and first bare minimum 
geometry generation takes place.

Here a short rundown of the different parts:


    Silhouette Operator Skeleton

After abandoning the Idea of the silhouette brush the silhouette 
operator is now starting to take shape. In this week I implemented a 
simple standard modal operator. It has currently three stages.

 1.

    Invoke, data for the silhouette gets allocated triggered by an
    alt-leftclick within sculpt-mode.

 2.

    Modal, the drawn shape while holding the keys is saved and a visual
    UI representation is updated.

 3.

    Exec, from the drawn shape 3D geometry gets generated and attached
    to the current PBVH. Afterwards data is cleaned up (more or less).

This is just a basis for the operator it will most likely get extended 
by several stages to be able to make changes after sketching a new 
shape. Similar to other operators you should be able to change the input 
values afterwards and may be able to reshape the drawn silhouette.


    Custom Draw-Calls

To get a visual feedback the operator needs a fitting UI. In this week I 
set the foundation for it by registering a custom draw call. Currently 
only a red contour is drawn but with the draw call in place this can 
easily be extended! One thing to note: The UI code uses OpenGL immediate 
draw calls which will get removed in 2.8 and will need to be ported 
later. -Shouldn’t be much of a problem though.


    Geometry Generation

The biggest challenge I faced this week was definitely the geometry 
generation. The existing sculpting system does not support topology 
changes with the exception of dyntopo. My current approach aims to make 
it possible to insert a mesh into the PBVH mesh tree system without 
rebuilding the whole tree. I am currently at the point where i can 
insert a mesh into a one-node-tree with it not crashing instantly. I 
have now got a rough idea of the PBVH structure and i think i will soon 
be able to insert into more complex topology. It is a lot of pointer 
reshuffling, buffer updating and indices magic which took longer than 
expected and I am just at the start. I may need to reevaluate my 
approach even though i am confident it will work.

The foundation for the Silhouette Operator slowly takes shape. With this 
I will soon be able to get into a more explorative workflow!

Best Regards,

Sebastian Witt

Current Branch status: 
https://developer.blender.org/rBce2671b0e29ba91e38d88858d5f5aba387d4e0c2

To try the Silhouette Operator press alt-leftclick in sculptmode and 
draw a shape. When drawn without overlap of a simple object a shape gets 
generated. (crashes most likely)

*

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