Manuel Massing wrote:
Hello David,
I saw few months ago some posts about asymetric frustum for a screen wall.
I got
a similar installation so I will have three displays, each of them with
asymetric frustum (the point of view is not centered on the screens). I
will have these parameters :
LeftScreen_Left_FOV
[...]
RightScreen_Bottom_FOV
Well, as Curt stated already, that depends on how these displays should
be aligned.
Assuming you want to simply combine three coplanar, untilted views (e.g. for a
multi-projector configuration on a single projection screen), and if these
parameters are angles relative to the viewing direction, it should
work as follows:
-create a symmetric frustum with FOV of
hor_fov = 2*max(-LeftScreen_Left_FOV, RightScreen_Right_FOV)
vert_fov = 2*max(-CenterScreen_Top_FOV,
Center_Screen_Bottom_FOV)
-calculate the viewport coefficients [in range 0..1] by
LS_l_coeff = 0.5 + 0.5*tan(LS_Left_FOV)/tan(hor_fov)
LS_r_coeff = 0.5 + 0.5*tan(LS_Right_FOV)/tan(hor_fov)
LS_t_coeff = 0.5 + 0.5*tan(LS_Top_FOV)/tan(vert_fov)
LS_b_coeff = 0.5 + 0.5*tan(LS_Bottom_FOV)/tan(vert_fov)
etc.
These can then be set via the property system, i believe. Curt will surely
be able to enlighten you on this.
That's the basic idea. You specify a larger "virtual" screen that has a
symmetric frustum and then each display get's assigned a portion of the
larger display. I realize this is probably not an industry standard way
to do it, and this approach probably can't cover every possible screen
configuration, but I needed something quick a few months ago, and this
approach meshed pretty well with the existing code.
I shold point out that there is some subtle wierdness depending on the
size of your display so for example, let's say you have 5 forward
displays. The center 3 are all parallel so they need to act as a single
larger fov display. If you want to assign 30 degrees field of view to
each of them, you would naturally pick a 90 degree field of view for the
center 3 and give each display 1/3 of that. However, you can't just
give the 2 edge displays an symmetric 30 degrees and have them match
up. There is some subtle aspect ratio stuff going on there that causes
problems. So what you'd need to do is setup the side channels as a 90
degree fov virtual display and give them 1/3rd of that, then they should
match up with the center channels.
At some point it would probably make sense to clean up the view pipeline
to handle this better, but time and priorities are always the big problem.
Regards,
Curt.
--
Curtis Olson http://www.flightgear.org/~curt
HumanFIRST Program http://www.humanfirst.umn.edu/
FlightGear Project http://www.flightgear.org
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