[visionegg] Re: map singratings on cylinder
- From: Andrew Straw <astraw@xxxxxxxxxxx>
- To: visionegg@xxxxxxxxxxxxx
- Date: Thu, 20 Dec 2007 15:23:35 +0100
Hi Kaspar,
I think the simplest way for now would be to approximate the cylindrical
projection you need with N perspective projections in adjacent
Viewports. For example, the left 100 pixels of your screen would be set
up with one viewport, the next 100 pixels with another, and so on. All
the viewports would be viewing the same Stimulus instance(s) and
displaying on the same screen, just viewing different angles. You should
be able to adjust the value of N to get acceptable projection error, and
the rendering speed shouldn't be too bad. By the way - do you have
optics that focus on such a screen? I'd be interested in hearing about
them...
As far as SinGrating3D -- it should be working, but I noticed that it's
not used in any of the demos, so it could have been broken for a long
time without me noticing. I'll check on this. And I do think
SinGrating3D is what you want to use with any kind of trick like the
above. The initial suggestion I have is to make sure that the camera is
actually looking at the stimulus. In the process of checking
SinGrating3D, I'll create a demo, so hopefully this will be working in
the next day or so...
Ultimately, the better approach to doing this type of this is what
OpenSceneGraph does with their osgDistortion demo. Namely, render the
image to a texture, and then distort that texture before sending the
image to the display. I'm currently investigating these ideas, but I
have no real implementation timeline that anyone should depend on.
Cheers!
Andrew
Kaspar Müller wrote:
Hi!
I would like to project singratings on a round screen, therefore I
need to correct the distortion in such a way that the grating-bars
have the same width everywhere.
I tried to map singratings on a cylinder, but somehow the projections
don't work. singrating3d doesn't work at all (is this class not
supported anymore? I didn't find it in the visionegg library
reference), and for singrating2d I didn't find out how to do it. I
tried to change vertex coordinates in the gratings class, and I also
tried to work with projections, but neither worked.
Unfortunately, I can't use the spheregrating class, since (1) I need
colors, and (2) I need the projection the other way round (at the
sides of the screen, the grating has to be narrower than in the center).
The mapping function for the horizontal coordinates should be
x'=R*tan(x/R), where R is the radius of the screen, x is the position
where the ray would hit a flat screen and x' is the horizontal
coordinate on the screen.
Any idea how I could manage this?
Thanks, Kaspar
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