POV-Ray : Newsgroups : povray.programming : first colum and last row active?? : Re: first colum and last row active?? Server Time: 19 Aug 2019 14:43:48 GMT
  Re: first colum and last row active??  
From: Aidy
Date: 27 Feb 2011 16:05:00
Le_Forgeron <jgr### [at] freefr> wrote:
> Le 27/02/2011 13:51, Aidy nous fit lire :
> > Le_Forgeron <jgr### [at] freefr> wrote:
> >> Le 26/02/2011 20:23, Aidy nous fit lire :
> >>> Hiya,
> >>>
> >>> I'm working on a project using porvay, and am currently looking through the
> >>> "Start_Adaptive_Tracing" method and inside the loop (over columns then rows)
> >>> there are two for loops which are commented as setting the last row inactive and
> >>> setting the first column inactive.
> >>>
> >>> I was just wondering what these actually do as I'm a little confused by them?
>
> > It's the release available on the main site, so version 3.6.2, June 2009.
> > The file I'm currently looking in is render.cpp in the Start_Adaptive_Tracing
> > method.
> > I'm getting confused at line 1535, which should be :
> >
> > for (xx = 0; xx < sub_pixel_size * Frame.Screen_Width + 1; xx++)
> >
>
> Remember that rendering in 3.6.2 was always from top-left corner, by
> full line, left to right first.
>
> In Adaptative tracing, the Block is 2^k subpixels, arranged as a square.
> subpixels on square lines are shared between squares.
>
> Last_Row is the storage of the subpixels from the previous line (there
> is no point in computing them again).
> On the same way, at the end of a block, the right side of the square
> become the left side of the new square.
>
> So far so good... but there is two caveat:
>  * on the first line, there is no previous line, so the .active of
> Last_Row is turned to false, to avoid the usage of bogus values.
>  * on each start of a new line, the block must be started afresh (you
> cannot reuse the right side for the new left side).
>
> Hope this helps.

Thanks for the response that makes sense.

Of the last row, which parts of it will relate to which pixel of the current row
being worked on?
I'm trying to convert the code to run in parallel and am finding this bit a
little confusing.

Thanks
Adrian


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