Hi Nick,
In the past I made some mistakes with mirrorring myself, so I
learned that simply mirroring triangles don't work well. I's just
a matter of disturbing your counterclockwise vertex sequence. I
would like to explain it with an example below:
Let's assume you created just one traingle at the right as follows:
CenterLine
1
|
/ \
|
/ \
| --------
|
2 0
now you mirror it to the left:
1 CenterLine
1
/ \ |
/ \
/ \ |
/ \
------
--------
0 2
2 0
You will notice that the nice counterclockwise direction at the
left is converted to clockwise at the right.
So, in my opinion you should not mirror the traingles but the
original coordinates. if so, you could mirror them using some
clever loop and create the traingles for the right after
mirroring.
Hope this helps,
Dirk
----- Original Message -----
From: "Nick Stark" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, June 09, 2003 10:53 PM
Subject: Re: [JAVA3D] Inverted Normals Question
> Thanks for your response, Alessandro.
>
> I am actually mirroring a coordinate system change transform. Here is one
> of the transforms I am trying to mirror.
> 0.997564, -0.069755, -0.000462, -0.000000,
> 0.067070, 0.957300, 0.281208, -0.006913,
> -0.019174, -0.280554, 0.959647, -0.04314,
> 0.000000, 0.000000, 0.000000, 1.000000
>
> And I multiplied this transform by the following (a scale of -1.0 applied
> to the x coordinates):
> -1.0, 0.0, 0.0, 0.0,
> 0.0, 1.0, 0.0, 0.0,
> 0.0, 0.0, 1.0, 0.0,
> 0.0, 0.0, 0.0, 1.0
>
> I'm not applying this transform to a shape, though...it is a bit more
> complex. To summarize, I need to mirror a coordinate system change
> (similar to one shown above), and use this transform in a series of
> transforms that are multiplied together. The product of this series of
> transforms is then used to transform a shape. Any ideas on how to mirror
> the transform without screwing up the normals?
>
> Thanks for your help,
> Nick
>
>
>
>
>
> Maybe this is a bug.
> How do you do this mirroring ??
> transform3D.setScale(-1) ? ( I guess the Java3D develop. team never
> imagined a negative scaling hehehehe )
> If so, may you can try another way as reverting X axis of the shapes, as
> below :
>
> private void mirrorShapeXAxis(Shape3D sh)
> {
> Appearance app = sh.getAppearance();
> if (app != null)
> {
> PolygonAttributes polyA = new PolygonAttributes();
> polyA.setCullFace(polyA.CULL_FRONT);
> app.setPolygonAttributes(polyA);
> }
>
> GeometryInfo gi = new GeometryInfo((GeometryArray)sh.getGeometry());
> Point3f[] coords = gi.getCoordinates();
>
> // mirror in X axis
> for(int i=0; i<coords.length;i++)
> {
> coords[i].x = - coords[i].x;
> }
> gi.setCoordinates(coords);
> // it reverse the normals - not mirror like
> //NormalGenerator ng = new NormalGenerator();
> //ng.generateNormals(gi);
> //gi.recomputeIndices();
>
> sh.setGeometry(gi.getGeometryArray());
> }
>
>
> Please report if it works or not.
>
> Alessandro
>
>
>
>
> ----- Original Message -----
> From: "Nick Stark" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Monday, June 09, 2003 10:09 AM
> Subject: [JAVA3D] Inverted Normals Question
>
> > Hi -
> >
> > I have a set of objects, all of whose normals are initially correct (all
> > lighting looks as it should).
> >
> > However, I apply a mirror transform to some of the objects, and when
> > viewing the new objects, it appears that the normals have been inverted
> on
> > the geometry. The lights still look correct for the objects that were
> not
> > mirrored, but the objects that are mirrored have dark faces and bright
> > backsides. The objects have not moved to such a position where this
> should
> > be the case, though. Is there some issue with the 3D API or is this a
> > problem that any of you have encountered before?
> >
> > Thanks for any help.
> >
> > Nick
> >
> >
>
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>
>
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