[yt-users] Unexpected behavior with camera.draw_domain and camera.draw_grids

[Sam Skillman]

Hi Noel,

Thanks for bringing this up.  I'm afraid I messed up (or really never had
it right to begin with!) how rgba channels are blended when using
grey_opacity=True renders.  I've posted a PR here:
https://bitbucket.org/yt_analysis/yt/pull-request/553/fix-for-grey_opacity-grid-line-drawing/diffthat
resolves this problem for me.  I don't expect it to take too long to
be reviewed and pulled in to the main repository, but if you are in a hurry
feel free to pull down the changes and test it out yourself. If you aren't
familiar on how to do that, please let me know.

Best,
Sam

BTW, very nice volume rendering!


On Tue, Jul 9, 2013 at 4:53 PM, Noel Scudder <noel.scudder at stonybrook.edu>wrote:

> Hi yt users,
>
> I'm having a lot of trouble recreating a volume rendering I did a couple
> of weeks ago. Specifically, when I try to add
> a boundary box to my snapshot through draw_domain() or grids through
> draw_grids(), the transfer function rendering fades very significantly,
> regardless of alpha value, and it did not behave this way before.
> However, it does not fade for cam.draw_box(... , ... , np.array([0.1, 0.1,
> 0.1, 0.2]) . Since draw_domain is basically just a call to draw_box, I took
> a look in camera.py and did a bit of testing, and the only difference is
> that the color array is np.array([1.0,1.0,1.0,alpha]) (where alpha=0.2) for
> draw_domain, and that is what seemed to be causing so much fade in the case
> of draw_domain. I didn't experience this problem before. Also, I don't know
> much about how this color stuff works, but I was under the impression that
> only the alpha value determined how bright the box is compared to the
> rendering underneath. Furthermore, when I decrease the alpha value, the box
> fades, but so does the rendering underneath, which should not be the case
> (?).
>
> I see the same behavior when doing draw_grids. Here is the image I created
> a couple of weeks ago: http://i.imgur.com/R0uhz2D.png
> And here is the image that the same script (very nearly) creates now:
> http://i.imgur.com/xcTmCMC.png
> The rendering underneath the grids is nearly invisible in the second one.
> If I stack another draw_grids onto the image after this, for a different
> level range, the rendering goes completely invisible, and the first set of
> grids almost does-- again, even with alpha values of ~0.05.
>
> For reference, here is the script I'm using:
>
> -----------------------
> from yt.mods import *
> pf = load("plt_derr_perr_grav_00020")
> field = "pressure"
> [variable definitions, cut out for clarity]
>
> pf.h
> pf.field_info[field].take_log=True
>
> tf = ColorTransferFunction((mi-1, ma+1), nbins=1.0e6)
>
> tf.sample_colormap(np.log10(2.0e21), 0.006, col_bounds=[mi,ma],
>                    alpha=[55.0], colormap="RdBu_r")
>
> tf.add_layers(6, mi=di, ma=da,
>               col_bounds=[pu,da],
>               alpha=26*na.ones(6,dtype='float64'), colormap="RdBu_r")
>
> [more layers, cut out for clarity]
>
> tf.grey_opacity=True
>
>
> c = [5.0e9, 5.0e9, 5.0e9]
> L = [0.15, 1.0, 0.4]
> W = (pf.domain_right_edge - pf.domain_left_edge)*1.25
> Nvec = 768
>
> cam = pf.h.camera(c, L, W, (Nvec,Nvec), transfer_function = tf,
>                   fields=[field], pf=pf, no_ghost=False)
> im = cam.snapshot(clip_ratio=6.0)
>
>
> im.add_background_color('black', inline=True)
> cam.draw_box(im, np.array([3.0e9, 4.0e9, 4.0e9]),
>              np.array([7.0e9, 6.0e9, 6.0e9]), np.array([0.1, 0.1, 0.1,
> 0.2]))
>
> nim = cam.draw_grids(im, alpha=0.08, min_level=1)
>
> nim.write_png('v1.png')
> -----------------------
>
> Am I doing something wrong or missing something obvious? Was the behavior
> of draw_grids and draw_domain changed with the new update? Thanks for your
> help!
>
> -Noel Scudder
>
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