利用者:Chingachgook/Gsoc2009/Diary

Learning the basics of COLLADA

May 8th

In COLLADA, primitives can be presented in 2 forms: polygons as <polygons> and <polylist> and triangles as <triangles> <trifans> and <tristrips>. Ignoring line primitives for now.

Since Blender allows only quadrilaterals and triangles, I will need to find out how to convert polygons to triangles or quads or a combination of these.

In case vertex normals are missing in a COLLADA file, they should be generated.

In COLLADA all coordinates are right-handed by definition - this is good since Blender uses right-handed too :-).

May 12th

How to determine if a MFace is a quad or triangle? According to exotic.c, if a face is quad then face->v4 is non-zero.

Now I know how to use addvertlist, addfacelist functions - progress!

Arystan introduced me to operator basics and menus based on operators.

May 17th

COLLADA DOM

There are two ways to work with COLLADA DOM: dae* classes and dom* classes. dae* classes provide a generic string interface to data. dom* classes, in contrast, provide direct access to data, i.e. floats are stored as floats. Although dae* classes are easier to learn than dom* classes (there's only a single daeElement class vs. tens of dom* classes), to keep code compact and efficient, I'll use dom* classes as much as possible.

May 18th

Studying a few build systems that Blender uses: make and scons.

Build with make succeded, but only release and with a few hacks. Debug build failed. Maybe later.

Built with scons before, very easy. Documentation on how to add a new library/module is available in the source tree in doc/blender-scons-dev.txt. Thanks jesterKing!

May 24th

Studying OpenCollada.

May 25th

• Coding environment prepared.
• Added "Collada Export" menu, the code is in wm_operators.c for now.

May 27th

Studying OpenCollada. It differs strongly from Collada DOM.

May 30th

Order of elements inside <Collada> (doesn't matter?) borrowed from examples in collada spec:

• asset
  • required tags: created, modified - create with StreamWriter::appendTextElement
  • up_axis(y up by default) - z up in Blender
• library_visual_scenes
• scene - is necessary for programs that allow only one scene
• library_geometries
• other

TODO:

• don't forget unit measurement conversions
• parenting

May 31st

Can not create <created> and <modified> with Asset class.

June 3d

prepareToAppendValues() calls another function prepareBaseToAppendValues() which creates the following

• **<float(or any other type)_array id = "" count = count * stride>
  At this step I have to insert data into <float_array> with appendValues().
  Next I close <float_array> and add the following
  **<technique_common>
  ***<accessor source = "" = "" stride = "">
  ****<param name = "" type = ""/>
  ****...
  ***</accessor>
  **</technique_common>
  *

with finish()

Now I know how to create <created> <modified>. It seems that add() method creates them automatically - cool =)

June 5th

Very basic geometry exporter is almost ready!
What is left:

• add blender's api

June 9th

Texcoords(UVs?) should be stored in <source>

Notes for personal reference

• COLLADA floats are actually C++ doubles
• COLLADA skinning and accessors
• How armatures work - will be very helpful on phase-2 of this project
  

Documentation

• COLLADA 1.5 specification