Normally culling of polygons with non-camera facing normals is an optimisation and can be turned off. Is this not possible in the 3d render libraries we're using?
Regards, Bevan On 1 Oct. 2020, 06:23, at 06:23, Cirilo Bernardo <cirilo.berna...@gmail.com> wrote: >Hi Mario, > > I never thought of a good way to manage the doubling of the vertices / >viewing from both sides. Since this is a problem of IGES as well as >VRML models (especially models not produced via MCAD) and it >makes no sense to me to complicate KiCad or the 3D viewer, maybe >one way to fix this would be to mark a bad model file by putting a >'_' at the end of the name, for example 'broken-model_.igs". Files >with that tag will be assumed to have bad normals and the vertices >will be doubled, otherwise normals are assumed to be good. > >Cirilo > > >On Thu, Oct 1, 2020 at 12:36 AM Mário Luzeiro <mrluze...@ua.pt> wrote: >> >> Thanks Cirilo! >> It has been small additions but resulted in good improvements... >> >> > results in a doubling of the triangular surfaces >> >> Could an option be added to this? ( both exporter and 3D-Viewer ) >> >> I didn't know / don't remember this condition, but I have an idea of >some inverted models cases too... >> >> Mario >> >> ________________________________________ >> From: Kicad-developers ><kicad-developers-bounces+mrluzeiro=ua...@lists.launchpad.net> on >behalf of Cirilo Bernardo <cirilo.berna...@gmail.com> >> Sent: 29 September 2020 04:51 >> To: KiCad Developers >> Subject: [Kicad-developers] Thanks for all the new work on the 3D >rendering. >> >> I see the latest changes from Mario Luzeiro and Oleg Endo. Wow .. >the >> 3D viewer has improved so much since Mario and I rewrote the code 6+ >> years ago. I'm very glad to see people continuing to make >> improvements. If anyone has time and wants a challenge there are 2 >> items I'm not very happy with in the 3D system. One is due to our >> early support for VRML only models as well as IGES models, and the >> second issue is due to mistakes I made in interpreting the VRML >> specification. >> >> 1. Legacy issue: the import of a VRML model (including those exported >> by kicad) or an IGES model results in a doubling of the triangular >> surfaces. So if you import a box described by 12 triangles that is >> double to 24 and if you export the model and import it again you get >> 48 triangles, and so on. The reason is that every facet is rendered >> from *both* sides and there is no algorithm for decimating the >> triangle data. The reason triangles were rendered from both sides is >> that many (well, *most*) VRML models which we used before the 3D >> overhaul were defective and the viewing normals were not guaranteed >to >> be correct (a facet described as viewable from the wrong side). IGES >> models also suffer this problem because the specification does not >> provide a requirement of a 'right-hand rule' to determine the Inner >> side vs Outer side of a surface and various CAD packages seemed to >> either use a right-hand rule, left-hand rule, or no rule. The >> triangle bloating problem will obviously have disastrous consequences >> for rendering time. As an alternative to decimating the triangles, >> any VRML model exported by KiCad could be specially tagged (similar >to >> how PDF uses some special comments) so that the importer does not >> double the triangles. The advantage of this would be that the VRML >> models generated from solid models via scripts could also be tagged >> and the doubleg could be avoided altogether where appropriate. >> >> 2. Incorrect interpretation of VRML spec. This is really a fairly >> minor issue and I don't believe there is any evidence that it has an >> impact on VRML models generated from solid models via >> OpenCascade/FreeCAD. Unfortunately I can't remember the exact >problem >> now, but at least one of the VRML groups are not correctly >implemented >> and as a result cannot be correctly referenced by more than 1 other >> group. Fixing the implementation could produce a more efficient >> exported model in some use cases. >> >> Cirilo >> >> _______________________________________________ >> Mailing list: https://launchpad.net/~kicad-developers >> Post to : kicad-developers@lists.launchpad.net >> Unsubscribe : https://launchpad.net/~kicad-developers >> More help : https://help.launchpad.net/ListHelp > >_______________________________________________ >Mailing list: https://launchpad.net/~kicad-developers >Post to : kicad-developers@lists.launchpad.net >Unsubscribe : https://launchpad.net/~kicad-developers >More help : https://help.launchpad.net/ListHelp
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