[Bf-committers] Blender success story, a couple of potential bugs and a feature request.

[Jonathan Merritt]

Hi Everyone,

I recently put Blender to use on an animation that was shown at 
Equitana, which is a big commercial horse show that was held here in 
Melbourne over the last weekend.  I gave Blender a big plug, pointing 
out that the animation would not have been possible without the efforts 
of Free Software programmers all over the world.  Here's a single frame:
    http://www.warpax.com/temp/forelimb-frame.png
The animation showed a moving horse limb (animated with real kinematics 
data that I pulled out of a refereed publication), and illustrated the 
function of one of the ligaments of the limb in storing elastic energy.  
I'm reluctant to post the full animation at this stage, since there are 
a few things that need to be fixed, and among them are the bugs listed 
below.

The limb is an animated armature (animated by rotation and location 
keyframes, not by an IK solver).  It has a basic animation that is set 
to repeat by having a cyclic extend mode.  In order to control the speed 
of the animation, the armature object has a Time IPO curve, whose slope 
varies through the animation to slow the limb down for a while before 
moving it back up to full speed.

I discovered that the rendering of objects parented by the "Use 
Armature" method seems to have a bug after the first frame, when motion 
blur is used.  The following is an example:
    http://www.warpax.com/temp/forelimb-ghost.png
Here, the ligament at the back of the bones is rendered in entirely the 
wrong place for just *one* of the motion blur frames (the others may be 
out of place as well, but I can't tell).  Note that this bug *does not* 
show up in the *first* rendered frame, only in subsequent frames, and 
does not appear in Blender itself when an animation is played using 
Alt-AKEY.  Hence, you can't observe the bug by rendering a single frame 
- it will only appear in the second frame of a rendered animation.

Also, the amount of blur applied to the animation does not seem to 
respect the relative progression of time indicated by the Time IPO 
curve.  Hence, even when I slowed the Time IPO curve to a complete halt 
(ie: horizontal line in the IPO window), the rendered objects were still 
being motion-blurred.  Is this the desired behaviour?

Finally, an option to render a flat mirror reflection map (as opposed to 
a cube-face environment map) would be really wonderful.  In this 
instance, with a heavily set-up scene, I was able to reflect things 
manually only by painstakingly selecting everything except the bone mesh 
objects and reflecting them in the ground plane.  This was quite a 
hassle, considering the simplicity of the effect from a technical point 
of view.

Jonathan Merritt.
PhD Student in Equine Biomechanics,
Faculty of Veterinary Science,
The University of Melbourne.