[Bf-python] IPO Exposure

[Roland Hess]

I've just signed up for the bf-Python list for two reasons:

1. I found I was reading the logs frequently anyway via the .org website.
2. I've identified a (hopefully) simple and very useful expansion to 
one of the modules.

Here's a rundown of point 2. First note that I would attempt this 
myself, but I have not been able to compile cvs after at least four 
different clean attempts on various machines over the past several 
months. Therefore, I have done what I think is good detective work 
that could make this easier for someone who has the mad skillz(tm) 
that I lack.

The Problem: Currently, when using the Ipo module of the API, the 
method addBezier of the IpoCurve class creates bezier points on the 
curve object with necessarily poor handles.  Code here:

bzt->vec[0][0] = x-1;
bzt->vec[1][0] = x;
bzt->vec[2][0] = x+1;
bzt->vec[0][1] = y-1;
bzt->vec[1][1] = y;
bzt->vec[2][1] = y+1;

In this sample from the addBezier definition in the python section of 
the source, x and y are the coordinates passed to the method, and the 
+-x and y assignments create handles one unit to the lower left and 
upper right of the provided point. For smooth animation purposes, 
this is worse than useless. If a Python scripter is dealing with only 
a few IpoCurves, they have the option of selecting that curve, 
entering edit mode and hitting SHIFT-H to make nice, smoothly aligned 
Bezier handles. However, in my scripting project there might be 
hundreds, if not thousands of Ipocurves, making that approach 
prohibitive.

Once points are added via the addBezier method, there is no way to 
alter the poor handles through the Python API.

Suggested Solution: expose the functionality of the SHIFT-H editmode 
command (and other related commands) to Python. The Blender code that 
seems to handle this functionality is:

sethandles_ipo_keys    found in
blender/source/blender/src/editipo.c   and

calchandles_ipocurve   found in
blender/source/blender/blenkernel/intern ipo.c

The method could be added to the IpoCurve class, with the format: 
ipocurve.setHandlestyle(Style), with style names corresponding to the 
available functions. This would complement the already existing 
setExtrapolation() and setInterpolation() methods.

Why Someone Should Do This: I have heard from one other Python writer 
(eeshlo), who had to abandon a scripting project (updating the Icarus 
script) because of this deficiency. That stinks. Anyone who animates 
with Python needs this update. So, whoever makes this addition would 
receive the undying gratitude of all Python scripters who would like 
to generate and record animation with Python.

Thanks. And by the way, if this request was completely inappropriate 
here, please let me know and I will humbly skulk away.
-- 
Roland Hess (harkyman)
IT Manager
Reed & Witting Company
Pittsburgh, PA