Re: NURB patch documentation error

[James W. W. <ja...@wr...>]

Bruce Director <ba...@ds...> wrote:

>Last year, in the process of working with Yotam Gingold on a NURB 
>bug, I thought that the row and column definitions were reversed. 
>I had provided an example where there were 3 "rows" and 58 
>"columns", but in order to render the NURB curve correctly I had to 
>set numRows to 58 and numColumns to 3.  Here is his answer:
>
>>I re-read the QD3D documentation regarding rows and columns, and I believe
>>what you think is "reversed" is actually correct.  To QD3D, your model's
>>controlPoints[0-2] are the first row, [3-5] are the second row, and so on.
>>Thus there are 58 rows and 3 columns.  It is good to know then that QD3D
>>is "correct".

That discussion doesn't say anything about what's u and what's v, so 
I don't see how it sheds any light on my argument.

>I think my misunderstanding had to do with thinking the 2-D array of 
>control points was stored as a 1-D array in column major order 
>instead of row major order.

I am aware that the array is stored in row major order, so if I have 
a misunderstanding, that's not it.

Let's consider the code in Geom Test, createGeomNURBPatch.  Since 
uKnots is an array of 8 values, and uOrder is 4, there should be 4 
control points on the u axis.  Similarly, vKnots has 6 values, and 
vOrder is 3, so there should be 3 control points on the v axis. 
However, numRows is 3 and numColumns is 4, which according to the 
documentation means that there are 3 control points in the u 
direction and 4 control points in the v direction.
-- 
   James W. Walker, ScriptPerfection Enterprises, Inc.
   <http://www.write-brain.com/>