Yep, it is... you can do this using several strategies... the naive on is to
simple define a constant
value for the x variation and the y variation in pixels related to world..
(e.g 1 pixel variation = 10 world units).
The other and more interesting strategy would be to calculate the x and y
pixel derivative related to world space. You can do this by simple
converting an unit segment at world x axis from world to screen (using
worldToScreen method) (do the same for y). The length in pixels of the
converted segment (in screen space obviously) is the derivative of world
space within screen space at the current camera space position (will need to
recalculate the derivatives for x and y after every camera move).
once your z axis is constant, it should be enough ;]
hope it helps...
Pablo
On Wed, Jul 9, 2008 at 12:24 AM, Jung Lee <[EMAIL PROTECTED]> wrote:
> Thank you always, Pablo.
> I am trying to drag and drop objects in a scene with mouse movements.
> Given mouse coordinates (x,y), a picked object would be translated
> into mapped world coordinates from the mouse coordinates. For example,
> I want kind of gluunproject function in OpenGL.
> If every screen pixels couldn't map into world coordinates, is
> possible to map the nearest? Z axis is constant in my application, and
> not changed. for example, i need to simply translate mouse(x,y) ->
> world(x',y',0). is it possible?
>
>
>
>
>
>
>
>
> On Sun, Jul 6, 2008 at 12:07 PM, Pablo Carneiro Elias
> <[EMAIL PROTECTED]> wrote:
> >
> > complementing thetha is azimuth and zenith is the other angle...
> >
> >
> > On Sun, Jul 6, 2008 at 1:05 PM, Pablo Carneiro Elias <
> [EMAIL PROTECTED]>
> > wrote:
> >>
> >> Jung,
> >> the mapping from world to screen is always possible within the camera's
> >> frustum, but the inverse is not true. It means that not every pixel of
> the
> >> screen has a map into world coordinates. Even if a point within the
> screen
> >> coordinates has a world mapping point, you can't actually know exactly
> which
> >> point it is if you don't constrain the Z value of the point in world.
> Thats
> >> because infinity points in world can map to a same point within the
> screen
> >> coordinate. So, if you're trying to make some sort of "Arcball" or
> Trackball
> >> feature using screen coordinates I can say that you don't need to
> convert
> >> those screen point into world points.. you just need a map from screen
> space
> >> to a open ball in R^3 using (centered at origin 0,0,0), for example,
> >> spherical coordinates (two angles)....
> >>
> >> to map from x,y into two angles (azimuth and zenith) you can do
> something
> >> like this:
> >>
> >>
> >> azimuth = ( 2*( x / screen_width ) - 1 ) * PI
> >> zenith = ( 2*( y / screen_height ) - 1 ) * (PI / 2)
> >>
> >> I've just came up with this mapping now, the're are many ways to build a
> >> trackball feature, thats just only an idea... to map the two angles
> above
> >> into a world vector within the open ball you can use:
> >>
> >> where r is an arbitrary ray of the ball (the biggest the ray the
> smallest
> >> is the rotation sensitivity)
> >>
> >>
> >> Hope it helps....
> >>
> >> On Sat, Jul 5, 2008 at 3:06 AM, Jung Lee <[EMAIL PROTECTED]> wrote:
> >>>
> >>> Dear OpenSG Users,
> >>>
> >>> I found most of the solutions for my problems with OpenSG in this user
> >>> forum! Thank you!
> >>> However, there is one thing still couldn't find a way - how to convert
> >>> 2D mouse coordinates into OpenSG world coordinates. Pablo helped me
> >>> understand it, but I couldn't implement it yet. I found there was one
> >>> method which translate the world coordinates into screen coordinates
> >>> in OpenSG (getWorldtoScreen). My questions is that there exists sort
> >>> of getScreentoWorld function in OpenSG. If not, how can I convert
> >>> mouse's x,y coordinates into world coordinates (x, y, z)?
> >>>
> >>> Thank you always!
> >>>
> >>> Jung
> >>>
> >>>
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