i'm actually use the "hardware method", with two clips planes in fact the front clip and the back clip of a camera locate just on the cut plane. works only with parallel projection (see my code bellow)
but the result is not very nice the cross section obtained is a dotted line... there are some gaps in the cross - section i join also the response of Mark Hood when i submit the problem to the list. If anyone have a better solution or any tricks to improve my cross section,i will be interested. regards Renaud the response of Mark Hood from Sun (june 2002) : The front and back clip planes are not really intended to solve this sort of problem (generating polygonal cross-sections). This clipping is done in hardware and is very system-dependent (although I am able to see the same result as you). It involves how the hardware triangle rasterizer is implemented. Triangles really have no depth; mathematically they are infinitely thin. Usually viewing a complete triangle edge-on will cause it to disappear unless special edge attributes are applied. Clipping away the front and back in an attempt to get a single pixel depth will mostly result in undefined behavior. You'll notice that the gaps are most prominent when the cylinder faces are edge-on to the camera. This problem is probably best solved mathematically. ----------------------------------------------- my code : Transform3D location = new Transform3D(); location.set(new Vector3f(.0f,.0f,.0f)); cameraD_.setlocation(location); cameraD_. ... .setViewPlatformBehavior(orbitBehavior); cameraD_. .. .setProjectionPolicy(View.PARALLEL_PROJECTION); cameraD_. ... .setBackClipDistance(0.0008); cameraD_. ... .setFrontClipDistance(0.00); //the cut plane Box BoxObj = new Box(3f, 3f, 0.01f, ap2); PlatformGeometry pg = new PlatformGeometry(); Transform3D translation = new Transform3D(); translation.setTranslation(new Vector3f(0.0f,0.0f,-0.001f)); TransformGroup translate = new TransformGroup(); translate.setTransform(translation); translate.addChild(BoxObj); pg.addChild(translate); cameraD_. ... .setPlatformGeometry(pg); --- "Raj N. Vaidya" <[EMAIL PROTECTED]> a écrit : > Well, a couple of ways that I could think of.... > > In software, you can generate a contour line through > the elements of > your GeometryArray - tris/quads. The contour line is > the locus of points > where the signed normal distance of the vertices > from the cutting plane > is equal to zero. In the case of a sphere, you will > get a circle - possibly > a great circle depending upon where you cut the > sphere. > > In "hardware", I think you may be able to use 2 > appropriately > oriented parallel ModelClip planes to achieve the > effect. This would > produce a ring actually, but if the distance between > the clip planes is > small enough it will look like a line contour. > Haven't tried it, > but looks like it would work. > > > Regards > > Vaidya > > > >On Wed, 9 Oct 2002 07:50:48 -0700, Scholl, Ed > <[EMAIL PROTECTED]> wrote: > > >Hello- > >Can anyone give me some pointers to draw the 2D > outline obtained from the > >intersection of a cutting plane with my 3D world? > i.e. if I specify a > >cutting plane that intersects with a sphere, I want > to display the resulting > >circle. > > > >-Ed > > > > > ========================================================================== ___________________________________________________________ Do You Yahoo!? -- Une adresse @yahoo.fr gratuite et en français ! Yahoo! Mail : http://fr.mail.yahoo.com =========================================================================== To unsubscribe, send email to [EMAIL PROTECTED] and include in the body of the message "signoff JAVA3D-INTEREST". For general help, send email to [EMAIL PROTECTED] and include in the body of the message "help".
