The Persistence of Vision Raytracer (POV-Ray).

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Attached to Project: POV-Ray
Opened by Grimbert Jérôme - 2010-03-29
Last edited by William F Pokorny - 2017-03-20

FS#91 - Slope pattern applied to object is not transformed afterhand

There is an big issue with the slope pattern: when the object it is applied to is instanced (again) with a transformation (in particular a rotation, as a translation would not impact.. but a shear might), the colours of the surfaces are changed.

object { p translate -5*x }
object { p rotate 220*y+20*x    translate 3*x }       

Nobody would expect the object to be different in appearance.
If slope {} is replaced with wood, all is fine. (as for others textures, i guess)

IMHO, the slope vector need to be adjusted for the later transformation(s) (so as to compensate the issue of using the Perturbed Normal vector).

This should not impact the AOI/FACING (experimental) patterns, as AOI definition is pretty clear about duplicating & transform if you think about it a bit, as well as FACING: for these two, it is expected to either use the ray(current point of view) or a fixed 3D point as reference. At the limit, discussion about moving the 3D point of FACING might also be opened to interpretation.

AOI/FACING are in task #19

Grimbert Jérôme commented on Tuesday, 30 March 2010, 13:47 GMT

The reason for closing might then question the interest for a separate “AIM” pattern (as per #19) which would update the vector so as to keep the values for transformations applied afterhand.

Christoph Lipka commented on Tuesday, 30 March 2010, 13:51 GMT

Reopened the task as a low-severity feature request rather than a critical definite bug.

[For the records, the task had been closed due to the behavior not being a bug, but rather intentional.]

Christoph Lipka commented on Tuesday, 30 March 2010, 14:15 GMT

An implementation of the requested feature would require pretty extensive changes, as the transformation information that would be required is not passed to the code actually evaluating the pattern. Passing the information all the way through may be a bit heavyweight. Furthermore, it would be necessary to "reverse-engineer" the transformation the object has suffered after the texture/normal/whatever has been applied, from (a) the total transformation applied to the object and (b) the total transformation applied to the texture, which is the transformations currently stored by POV-Ray.

William F Pokorny commented on Monday, 20 March 2017, 13:36 GMT

Now tracked on github as issue #254.


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