OK, I'm with you now. Another way might be to just draw the images in 3d as I suggested, turn off depth testing (so the sprites draw over the background), and scale the size by the inverse of Z to prevent them shrinking. That would put more of the maths into QC rather than JS/math patches, which could be faster (useful when you're doing lots of points in an iterator).
Chris 2009/11/3 Sune Watts <[email protected]>: > Hiya Chris > > Allright, I dug into the maths and seem to have solved it. I'll share it > here, as I feel it is useful. > > QC file is attached this email. > > To project a 3d point onto space, use this formula and z-axis scale factor: > > > var scaleFactor = 0.58; > screenX = obX * (1 / ( 1 + (-obZ * scaleFactor) )); > screenY = obY * (1 / ( 1 + (-obZ * scaleFactor) )); > > --- > I need it for a top layer of 2d overlays and pointers that do not scale, but > accurately follow a moving 3d scene. > > > All the best > Sune Watts > --- > > > On Tue, Nov 3, 2009 at 1:34 PM, Chris Wood <[email protected]> wrote: >> >> If you really want to do it manually, you'll need to learn some maths. >> You need to calculate the distance of a point on a sphere from the >> camera (the camera position in QC is (0,0,-1) if I remember right) to >> determine size and perspective transform. >> >> I don't understand why you need to convert though - if you have the >> xyz position, why not just tell QC to draw your image at that xyz >> position? >> >> You could also use the 3D transform patch perhaps? >> >> Chris >> >> >> 2009/11/3 Sune Watts <[email protected]>: >> > Sorry if I was unclear: >> > >> > How to translate an (x, y, z) point into (x, y) screen coordinates -- >> > >> > For example, you have a rotating globe and want to know the screen >> > coordinates of a certain city on the globe. >> > >> > >> > Best regards >> > Sune Watts >> > >> > >> > --- >> > >> > >> > On Tue, Nov 3, 2009 at 11:02 AM, Chris Wood <[email protected]> wrote: >> >> >> >> QC supports 3D space already. There's 2 ways to show a 2D image: >> >> Billboard (this is best for overlays and the like, and is 2D based) >> >> and Sprite (this is similar to billboard, but exists in full 3D space >> >> so you can move it on Z, and rotate on all 3 axis. >> >> >> >> Most likely, sprite will cover your needs. >> >> >> >> Chris >> >> >> >> >> >> 2009/11/3 Sune Watts <[email protected]>: >> >> > Hello all; >> >> > >> >> > I need to pin a 2D billboard onto a (moving) point in 3D space. >> >> > >> >> > I haven't been able to find any info on the z-axis scaling QC >> >> > employs. >> >> > >> >> > Has anybody got a handle on mathematically converting a point in 3D >> >> > space to >> >> > 2D screen space? >> >> > >> >> > >> >> > All the best >> >> > -SW >> >> > >> >> > _______________________________________________ >> >> > Do not post admin requests to the list. They will be ignored. >> >> > Quartzcomposer-dev mailing list >> >> > ([email protected]) >> >> > Help/Unsubscribe/Update your Subscription: >> >> > >> >> > >> >> > http://lists.apple.com/mailman/options/quartzcomposer-dev/psonice%40gmail.com >> >> > >> >> > This email sent to [email protected] >> >> > >> > >> > >> > _______________________________________________ >> > Do not post admin requests to the list. They will be ignored. >> > Quartzcomposer-dev mailing list >> > ([email protected]) >> > Help/Unsubscribe/Update your Subscription: >> > >> > http://lists.apple.com/mailman/options/quartzcomposer-dev/psonice%40gmail.com >> > >> > This email sent to [email protected] >> > > > > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Quartzcomposer-dev mailing list ([email protected]) > Help/Unsubscribe/Update your Subscription: > http://lists.apple.com/mailman/options/quartzcomposer-dev/psonice%40gmail.com > > This email sent to [email protected] > _______________________________________________ Do not post admin requests to the list. They will be ignored. Quartzcomposer-dev mailing list ([email protected]) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/quartzcomposer-dev/archive%40mail-archive.com This email sent to [email protected]
