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-   -   Question about postScale while linking two objects (https://forum.worldviz.com/showthread.php?t=5203)

mape2k 10-24-2014 08:49 AM

Question about postScale while linking two objects
 
Hello all,

here is what I want to achieve:

Link an object (destination) to the viewpoint (source), so that it moves with the viewpoint BUT at a different speed. E.g. if the viewpoint moves 10m, the linked object should only move 2m.

I managed to do that with the postScale command. However, the scaling is also applied to the inital offset of the destination object. This is a problem, because I want to destination object to start out at a certain offset, independent of the speed scaling.

I tried to manually set a transformation matrix but failed so far. I included a small sample script. Here, the pigeon starts out at an offset of [3,0,3] from the viewport. I want it to move with the viewport, but at a different speed.
If I apply a postScale, the pigeon will NOT start out at an offset of [3,0,3], but at the offset multiplied by the scale.

Code:

import viz

model = viz.add('pit.osgb')

pigeon = viz.addAvatar('pigeon.cfg')
pigeon.setScale(3,3,3)


# with linking
pigeonlink = viz.link(viz.MainView, pigeon, offset = [3,0,3], mask = viz.LINK_POS)

postScale = pigeonlink.postScale([0.8,0,0.8], target = viz.LINK_POS_OP)

viz.setMultiSample(8)
viz.fov(90)
viz.go()

Thanks for your help in advance!

farshizzo 10-24-2014 08:58 AM

I think you need to apply the offset after the scale. Try the following:
Code:

pigeonlink = viz.link(viz.MainView, pigeon, mask = viz.LINK_POS)
pigeonlink.postScale([0.8,0,0.8], target = viz.LINK_POS_OP)
pigeonlink.postTrans([3,0,3], target = viz.LINK_POS_OP)


mape2k 10-24-2014 09:20 AM

That worked wonderfully, thanks!

I the meantime, I also managed to fix it by manually correcting the offset by the scaling factor * initial offset.

Your solution is much more elegant, thanks again!

mape2k 10-24-2014 09:38 AM

EDIT: fixed.


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