Decals in OpenRocket: a not-so-quick and fairly complete tutorial

[K'Tesh]

Ok. If I want to print the decals, how would I do that?

Unless the full decal set is hidden in the .ork file, you shouldn't rely on OR for the decals. Yes, I've only just started hiding them in my .ork files. However, the high DPI images of the decals can sometimes exceed the file size possible for OR to manage (or at least share here).

The best way to print the decals is to get a good scan of them (from JimZ's site, or found here on TRF), or a clean file with a simple (say white) background, and print it from that. OR basically creates wraps for the entire part being decaled, and as you can see in Neil's post above they have to be mirrored to be displayed properly if they appear on fins, ruining them for printing and using on an actual rocket.

 

[neil_w]

Unless the full decal set is hidden in the .ork file, you shouldn't rely on OR for the decals. Yes, I've only just started hiding them in my .ork files. However, the high DPI images of the decals can sometimes exceed the file size possible for OR to manage (or at least share here).

The best way to print the decals is to get a good scan of them (from JimZ's site, or found here on TRF), or a clean file with a simple (say white) background, and print it from that. OR basically creates wraps for the entire part being decaled, and as you can see in Neil's post above they have to be mirrored to be displayed properly if they appear on fins, ruining them for printing and using on an actual rocket.

This is correct. I usually use 100 DPI images for my ORK files, and then redo everything at 300 dpi for printing. You *can* use 300 DPI images for your ORK file if you want, though. It does bloat the ORK file and also it causes OR to use a lot more memory when displaying. But it does work.

 

[neil_w]

Tube Decals, Inside and Out

Much like fins gained the ability to have different appearances on each side, tubes (body tubes, inner tubes, and tube fins) have gained the ability to have different appearances for inside and outside.

Let's use this decal on a 1" long x 4" diameter ring:

By default that decal is applied to both outside and inside. It looks like this:

Note that the ring is rotated 180 degrees so you can see what's inside. On the inside, the decal is not mirrored (text is still correct), but it points exactly backwards instead of forwards.

Let's tell OR to use different appearances for inside and out, and then assign the same texture for the inside:

Well, it looks exactly the same as before. So now there are two ways to get that oriented correctly. One is to create a new decal image, rotated 180 degrees. Simpler, though, is to use the "Rotation" control in the Appearance tab to do it for you:

And now, we've got the inside and the outside of the ring under control. To be honest, decals on the inside of tubes are pretty uncommon, but it's good to know how it works anyway. It *is* pretty common to have a different color on the inside of a tube (especially for tube fins and pods), and it is good that it is now possible.

There is one neat trick we can play with these tube decals, which will be covered in the next post.

 

[neil_w]

Stupid Transparency Tricks

This trick was already posted in a separate thread, but I wanted to put it here as well for reference, since it's fundamentally a decal trick.

It turns out that the non-transparent parts of decal images are always rendered opaque, even if the underlying component is not. This becomes useful for visually representing tubes that are not cut square, and some other stuff as well.

Let's take this decal. The triangle up top that is showing white here is actually transparent in the PNG image.


Now let's take a completely transparent tube and apply this decal:

It's hard to see what's going on here because the decal is showing on the inside as well, rotated 180 degrees. So let's do what we did in the previous post: use separate appearances inside and out, set *both* to fully transparent (Opacity = 0), and then use the same decal on the inside, rotated 180 degrees:

The red part is the transparent part at the front of the tube, showing red because the component is selected. Here it is unselected:

That's cool. As noted, you can't get rid of that little ring at the front, it's out of our control for now. This sort of thing looks best when the wall thickness of the tube is zero, so it's not quite right as far as simulation goes. You need to fiddle and fudge as necessary.

Might as well finish up where we're going with that tube. Let's use this decal instead for the inside:

Same exact shape, just a different color. And the result is:

I think we can agree that's pretty cool. Whether it is *useful* or not... well, sometimes cool is enough.

You can achieve all kinds of crazy visuals with transparent decals. This render has elaborately cut tube fins, and a transparent nose cone with a decal that makes it look like the nose it in two separate pieces. ORK is attached:

One final caution on this trick: the rendering engine here is pretty simple, and does not handle multiple transparent objects layered on top of one another. A transparent object will occlude another transparent object behind it. You can see the effect on the top tube fin above: it is blocking the next tube fin behind it, even though in theory it should show it through the transparency. So, unfortunately, you can't create elaborate layerings of transparent objects. That doesn't really diminish the fun you can have goofing around with this, though. Enjoy!

 

[kjhambrick]

Thanks @neil_w and @K'Tesh for all the .docs.

Still studying all thread but what fun !

-- kjh