This modifier is currently under development. This repository should be considered unstable.

This modifier will transform 3-D geometry into 2-D billboards (planes) orientated to face a reference object. There are a few possible uses which come to mind at this stage in development: as an alternative to wireframe/skin for creating geometry that can be rendered from edge-only meshes; or as a method for simplifying complex geometry to a single plane-texture pair.

Throughout development, I will be documenting my progress incrementally in this README file so that this project might be useful for anyone interested in attempting to implement their own Blender modifier (or, at the very least, remind me of how to implement a modifier next time I forget).

From http://wiki.blender.org/index.php/Dev:Doc/Tools/Git

git clone git://git.blender.org/blender.git
cd blender
git submodule update --init --recursive
git submodule foreach git checkout master
git submodule foreach git pull --rebase origin master

I wanted to keep my modifier development branch separate from my main blender branch. I also wanted the new branch to only include an initial snapshot of the blender development branch and squashed merges in order to keep things as clean as possible.

The new branch was created as an orphan (initialised with the contents of master).

git checkout master
git checkout --orphan billboard
git commit -m "Blender merge 0"

The new branch was then linked to the remote GitHub repository and the contents pushed.

git remote add github https://github.com/ilent2/Blender-Billboard-Modifier.git
git fetch github
git push [-f] github billboard:master

Finally, to merge in new changes from the Blender master branch I would use the commands:

git merge --squash master
git commit -m "Blender merge <N>"

The next task in developing this modifier was to create place holders for the modifier implementation. My initial guide was the slightly outdated tutorial at http://wiki.blender.org/index.php/User:Enjalot/Creating_a_custom_modifier . The easiest approach is to find a modifier that is similar to the modifier we intend to develop and running grep on the Blender source tree with terms related to the modifier.

The changes needed to implement a new operator are divided into four categories:

• modifier implementation
• makesdna entries (modifier data structure)
• makesrna entries (RNA structure, UI text, description, icon name, ...)
• Declaration and drawing of an icon
• Python bl_ui user interface code

A full summary of changes can be found in the commit ilent2@f182cdc910c477079a434cd31186337cee29a147

The basic idea of this modifier is to create a plane orientated towards a reference object for each edge in a mesh. The length of the plane is controlled by the edge length and the width by a thickness parameter in the modifier UI. At a later stage it might be possible to handle faces, vertices or even curves.

This initial prototype requires the addition of two UI properties. We declare these new properties inside the BillboardData structure in DNA_modifier_types.h.

/* Billboard Modifier */
typedef struct BillboardModifierData {
  ModifierData modifier;

  // The two new properties offset and object
  float offset, pad;
  struct Object *object;

} BillboardModifierData;

Notice the addition of the padding variable. Blender DNA must be aligned, there are a couple of pages which describe this, a quick Google returned this page http://wiki.blender.org/index.php/Dev:Source/Data_Structures/DNAStructs .

The new RNA entries for the offset and object where copied from the Wireframe and Mirror modifier RNA declarations respectively. The Mirror modifier uses a reference object in roughly the same way as our modifier. The offset property is just a float so there is not too much to declaring this property.

In our main modifier source file, we have implemented a rough version of the modifier (probably not very efficient nor very clean and orderly). The other addition to the main source file are the updateDepgraph and foreachObjectLink functions. These two functions where pretty much copied verbatim from the mirror modifier source code. The first function allows the modifier to respond to changes to the reference object in real time. The second function seems to be related to loading and linking.

ilent2@4e7da3523c7d1e8be12597a1fbcd4360ed802b90