Re: texture map irregularities OR pimento problems

["Rick Towler" <rtowler(at)u.washington.edu>]

Update: On another machine with the same graphics adapter but different
driver revision the first case renders exactly like the software renderer.
Which is good, I guess (but this is actually farther away from what I want).
I still don't understand why I can't see the inside of the green orb in the
first case.

-Rick


"Rick Towler" <rtowler@u.washington.edu> wrote in message
9gtvnl$q08$1@nntp6.u.washington.edu">news:9gtvnl$q08$1@nntp6.u.washington.edu...
> I have been experimenting using the alpha channel to represent confidence
in
> a data set.  I produce a polygon object representing the data and then
> texture map the polygon accordingly.  But, I have run into an issue that I
> can't resolve.
>
> I have attached a simple example (requires at least IDL 5 something and 24
> bit display).  I create 2 orb objects, one green (the olive) and one red
> (the pimento).
>
> At first I place the olive in front of the pimento, then I make the near
> surface of the olive transparent.  Rendering in hardware for the most part
> works except between the last opaque vertices and the first transparent
> vertices I get a white (background color) ring where you can actually see
> thru the entire olive to the pimento behind it.  If your imagination is
> failing I'll remind you that we are just supposed to be looking into the
> inside of the olive, we shouldn't actually see the pimento thru the olive.
> Rendering in software, things get even more wacky.  I don't see the inside
> of my olive at all.  Xray vision I guess.  What is interesting to note is
> that this ring I get when rendering in hardware renders just like the all
of
> the transparent vertices in software.
>
>
> I then flip the pimento and the hole in my olive.  The pimento now is in
> front of the olive and the "hole" is created on the back side of the green
> orb.  Now when I rotate the olive around so I can see in my hole, things
> look pretty good.  The astute observer will notice that the ring is still
> there (you will see a little red pimple if viewed from the right angle)
but
> otherwise things look good.  In software mode, things seem to work.
>
>
> What is going on in the first case?  Why does software rendering fail to
> render the inside of the olive?  What am I missing?
>
> I would be happy to provide images upon request.
>
> -Rick Towler
>
>
> ;pimento example
>
> container = obj_new('IDL_Container')
>
> ;create a rainbow texture map with varying alpha
> palette = obj_new('IDLgrPalette')
> palette -> LoadCT, 13
> container->add, palette
>
> imagedata = bytarr(4, 256, 256, /nozero)
> for a = 0, 255 do begin
>     for nc=0,255 do begin
>         imagedata[0:2,a,nc] = palette -> GetRGB(nc)
>         imagedata[3,a,nc] = a
>     endfor
> endfor
> texmap = obj_new('IDLgrImage', imagedata, interleave=0, $
>         blend_function=[3,4], /interpolate)
> container-> add, texmap
>
>
> ;a model to stick things in
> model = obj_new('idlgrmodel')
> container -> add, model
>
>
> ;some reference orbs
> pimento = obj_new('Orb', pos=[0,0,-3.0], radius=1.0, color=[255,0,0],
> density=2.0)
> container-> add, pimento
>
>
> ;something to texmap
> olive = obj_new('Orb', pos=[0,0,0], radius=2.0, color=[255,255,255],
> density=2.0)
> container-> add, olive
>
>
> ;add atoms from back to front
> model -> add, [pimento, olive]
>
> ;get the olive's vertex data
> olive -> getproperty, data=vtex
>
>
> ;calculate an array of latitudes for each vertex point
> vtex_dims = size(vtex, /dimensions)
> latitude = fltarr(vtex_dims[1])
> nf = sqrt(total(vtex^2,1))
> for n = 0, vtex_dims[1] - 1 do begin
>     vtex_norm = vtex[*,n] / nf[n]
>     latitude[n] = acos(vtex_norm[2] / sqrt(total(vtex_norm^2.))) * !RADEG
> endfor
>
>
> ;set the texture coordinates
> ;create a "bowl" by making the positive z verticies with latitudes
> ;less than 45 deg transparent.  The result is an orb with a hole in
> ;the side.
> texcoords = fltarr(2,vtex_dims[1], /nozero)
> texcoords[1,*] = .65  ;pick a nice green color for our olive
> texcoords[0,*] = 0.99
> ;set the opacities to ~0.0 at lats lt 45.
> i = where(latitude lt 45.)
> texcoords[0,i] = 0.01
>
>
> ;set some properties
> ;note that you have to set reject=0 since by default orbs set it to 1
> olive -> setproperty, texture_map=texmap, texture_coord=texcoords, $
>     /texture_interp, /zero_opacity_skip, reject=0
>
>
> ;take a look at what we got
> xobjview, model, /block
>
>
> ;now flip this whole deal in the z direction
>
> ;move our pimento
> pimento -> setproperty, pos=[0,0,3.0]
>
>
> ;cut the top off of the other side of the bowl where
> ;latitude is gt 180. - 45.
> texcoords[0,*] = 0.99
> i = where(latitude gt 180. - 45.)
> texcoords[0,i] = 0.01
>
> olive -> setproperty, texture_coord=texcoords
>
>
> xobjview, model, /block
>
> ;cleanup
> obj_destroy, container
>
> end
>
>