# Asymptote: How to draw surfaces with more than four vertices without "seams?"

In Asymptote 3D, I need to draw surfaces with more than 4 vertices, but when I do, either it simply doesn't work (I can't reproduce this in a simple example, but can provide a more complicated case where this happens if it is helpful) or a seam appears, as in the example below:

``````settings.prc = false;
defaultpen(fontsize(10pt));
import three;
import graph3;
import patterns;
size(11cm,0);

currentprojection=perspective((10,-20,10));
currentlight = (3,-2,3);

render render = render(compression=Low, merge = true);

draw(surface((0,0,0) -- (1,0,0) -- (1,1,0) -- (0.5,1.5,0) -- (0,1,0) -- cycle), lightblue+opacity(0.5), render);
``````

Running this command

``````asy -noprc -render 0 -f pdf example.asy
``````

gives the following image:

Is there a way to get rid of the dark blue "seam?"

• Currently this doesn't look like a tex question - asymptote and tex are not the same thing. Please add some more detail and include a minimal working example.
– user30471
Sep 22 '14 at 21:47
• Hello, I compiled your example and I had no "seam" (in the OpenGL 3D-render, and in the final eps/png file) ? Could you precise asymptote version, system ?
– O.G.
Oct 28 '14 at 21:35
• What command do you use to render this? Also, if you are generating a "vector" PDF it seems that is natural for overlaps to appear. I found this with TikZ/pgfplots for example: tex.stackexchange.com/questions/58227/…
– alfC
Nov 13 '14 at 2:43
• @Andrew Did you notice the `asymptote` tag?
– user10274
Dec 12 '14 at 21:11

It seems that the "seam behavior" depends on the pdf viewer and the `-render` option. "Seam" problems appear with opacity and `-render=0` option: depending on the pdf viewer the superposition of a common border of the two patches creates such a behavior.

With `-noprc` and `-render=0`, we have "seam" with Okular, acroread, gv (the image is vectorised). No "seam" with evince, mupdf, zathura. I have transparency problems with evince and zathura. mupdf is fine.

With `-noprc` (so the OpenGL render is used and a bitmap image is produced) there is no "seam" at all.

To be precise, all the version are up-to-date Debian Sid.

As explain in the documentation, `-render=0` is very limited.

• Interesting, thank you. See my edited question to see the result when I get rid of "-render 0". Feb 24 '15 at 13:14
• Try the option `-glOptions=-indirect`. See the documentation asymptote.sourceforge.net/doc/three.html#three about some OpenGL driver problems. Try also `asy -V` interactive mode and keyboard `e` to export.
– O.G.
Feb 25 '15 at 20:56
• I just tried it again, and apparently `asy -noprc -f pdf example.asy` works fine suddenly. (Adding `-glOptions=-indirect` works too, but apparently is not necessary.) Perhaps system updates fixed it? Feb 27 '15 at 0:52