POV-Ray : Newsgroups : povray.binaries.images : How does cylindrical warp work? : How does cylindrical warp work? Server Time: 18 Jun 2019 07:15:09 GMT
  How does cylindrical warp work?  
From: Cousin Ricky
Date: 4 May 2019 04:49:30
OK, so it turns out I don't understand cylindrical warp after all.

A few years ago, I introduced cylindrical textures to CoffeeMug in the 
object collection.  Looking back to see how I could adapt the code to 
work with cylinders or cones oriented in different directions, I 
realized that I had never specified any orientation for the coffee mug! 
I went back to RTFM to see how it would be done.

The orientation keyword would seem to do the trick, but the doc says 
that the default is <0, 0, 1>.  My coffee mug is vertically oriented, 
and my code works without changing the default.

I whipped up a test scene to investigate the orientation keyword.  I 
used Parse_String() to make sure that the SDL for each test case exactly 
matched the annotation text.  In these scenes, p_Test is defined as 
pigment { square scale 1/8 }.

True to the docs, orientation z matches the default, not orientation y. 
And somehow, orientation z corresponds to a cylinder with axis y.  I do 
not understand why this is; and more importantly, I have no clue how to 
get a cylindrical warp to match a cylinder of arbitrary orientation. 
How does it work?

Also, I am bemused by the cylinder illustration, which somehow works 
with a vertical cylinder and orientation y, and I am befuddled the 
spiral at the top; but since the example uses a non-default dist_exp 
(whose explanation soars way above my head), I don't know if it's relevant.

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Download 'test_cylindrical_warp1.jpg' (37 KB)
Download 'test_cylindrical_warp2.jpg' (46 KB)
Download 'test_cylindrical_warp3.jpg' (39 KB)
Download 'test_cylindrical_warp4.jpg' (48 KB)

Preview of image 'test_cylindrical_warp1.jpg'

Preview of image 'test_cylindrical_warp2.jpg'

Preview of image 'test_cylindrical_warp3.jpg'

Preview of image 'test_cylindrical_warp4.jpg'


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