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List:       mesa3d-dev
Subject:    [Mesa3d-dev] Further progress on trimmed nurbs in display list with
From:       ruediger janecke <ruediger.janecke () cadvice ! de>
Date:       2008-04-21 16:45:45
Message-ID: 480CC4B9.2040002 () cadvice ! de
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Dear mesa3d-team,
working on the problem of the "trimmed nurbs in the display list with
example 'trim.c' " -
however "trim.c" was modified the use the display list -,
I was able to finalize the correction (a recommendation of a fix).

Picture #1 shows "trim.c NOT using the display list" with the mesa-OGL 7.0:
everything OK.
Picture #2 shows "trim.c using the display list" with the mesa-OGL 7.0:
the triangles along the trimcurves are missing.
Picture #3 shows the same object with my partial fix:
there is a "cut" (some of the triangles are still not displayed)
Picture #4 shows the the same object with my complete fix:
"trim.c NOT using the display list" looks the same as
"trim.c using the display list".

Give me some more time for code verification, code clean up and tests.
If there are any questions or remarks, pls. let me know.
It was a pleasure to me, to make a contribution to this great piece
of software.
With kind regards,
Ruediger Janecke




My last mail (from 04/15/2008 04:06 PM)
ruediger janecke wrote:
> Dear mesa3d-team,
> 
> as promised, I'm working on the problem of trimmed nurbs-surfaces
> in the display list with the red book example "trim.c" - the latter
> so far modified, that the display list is used.
> 
> Just as an introduction, the first picture shows the original "trim.c".
> The 2. picture shows "trim.c" using the display list: there is a lot
> of missing things (triangle like surfaces) along the trimming curves.
> 
> I found out, there are sequences of opcodes on the display list,
> which seem not being used.
> Such a typical sequence of opcodes is:
> | EXT_0 | EVAL_C2 | EVAL_C2 | EVAL_C2 | END |
> Interpreting those sequences, I received the result of picture #3.
> 
> You may notice the "cut" on the left, very low part of the surface.
> To identify the reason, I just output the supplementary triangle
> surface onto the screen (picture # 4): what can be seen, is that
> the lower left part differs from the lower right part.
> That is the reason of the mentioned "cut".
> For some reason, there are either missing or wrong supplementary
> triangle surfaces in the lower-left region of the part.
> 
> To find out more about it, what is going on there:
>  From the information of the display list, I generated
> STL-format-like (triangle) surfaces just from the u/v-parameters and
> converted the STL-file to IGES to be able to display the u/v-surfaces
> in "CADVICE.View" and then to obtain information about them by
> clicking on the surfaces in the "defect"  area  (picture # 5).
> I found surfaces without any extension in v (y).
> Those surfaces are the lines with the little yellow squares
> (controlpoints).
> The picture also shows, that the left side is diffent from the right
> side.
> Through the "id" of the surfaces on the IGES-file, I found the
> "coordinates" (u/v) of the surfaces and could compare them with the
> information on the display list.
> This seems to proof the suggested code fix to display the obove
> mentioned sequences of opcodes, BUT leaves open the question of the
> "cut" produced by the line-like "triangele" surfaces.
> 
> I believe, the information on the display list is so far correct,
> but there is (also) another problem, when triangle surfaces along
> trimming curves are written to the display list.
> Again, everything described here, just happens in conjunction with
> the display list.
> 
> I will continue working on this and will let you know progress and my
> suggestion of code fix.
> Give me a few weeks.
> If there are any questions or comments, pls. let me know.
> Kind regards,
> Ruediger
> 
> 

["trim_direct_on_screen_ok.jpg" (image/jpeg)]
["trim_w_display_list_not_ok.jpg" (image/jpeg)]
["trim_w_display_list_w_fix_not_yet_ok.jpg" (image/jpeg)]
["trim_w_display_list_w_fix_now_ok.jpg" (image/jpeg)]

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