Enrique Dumas wrote: > " canvases[canvasId].getInverseVworldProjection(leftInverseProjection, > > rightInverseProjection);" > > and why it is hard to compute it by myself ?
I'm probably the wrong person to answer this, because I don't know the minute details of the j3d implementation. I'll just answer in hand-waving terms terms and then let the j3d guys rap me over the knuckles when I say something stupid. The view frustum is basically a description of the limits of visibility in coordinate system of the virtual world. Building up this information takes quite a lot of work if you don't have everything available to you. The frustum consists of six planes, which together define a bounding box. You can roughly calculate the sides of this box using the field of view information, the aspect ratio of the screen and the clipping planes. In making these calculations you then need to know how the screen coordinates are being mapped to the world coordinates - the window eyepoint policy (and maybe the movement policy?). Each of these stuff around with the final projection information. Unfortunately it is not just a simple UVN camera model we're dealing with here. In one of our examples, the actual view frustum describes the 5 sides of a cave. Usinng the j3d API call takes that into account for us. If you don't use that call, you also then have to work out how many canvases are being used, what their physical location is (Screen3D info) and then build up your own frustum from the multiple smaller frustums. If you are doing that every frame, it's soon going to be a performance issue. Even then, I'm not entirely sure you'd get the right value anyway. Notice how many people have problems understanding how just the basic clip policy works without even thinking about multicanvas issues. There's definitely still a large amount of black-magic going on down in the bowels of the Java3D view model. -- Justin Couch http://www.vlc.com.au/~justin/ Java Architect & Bit Twiddler http://www.yumetech.com/ Author, Java 3D FAQ Maintainer http://www.j3d.org/ ------------------------------------------------------------------- "Humanism is dead. Animals think, feel; so do machines now. Neither man nor woman is the measure of all things. Every organism processes data according to its domain, its environment; you, with all your brains, would be useless in a mouse's universe..." - Greg Bear, Slant ------------------------------------------------------------------- =========================================================================== 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".
