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

The Rocketry Forum

Help Support The Rocketry Forum:

neil_w

Yum yum rockety goodness
TRF Supporter
Joined
Jul 14, 2015
Messages
11,460
Reaction score
4,294
Location
Northern NJ
Thanks for that, I've been meaning to try out the nose cone. It looks like it is treated like a tube, but with the front shrunk down, so the decal image is distorted. It would be an interesting challenge to do something useful with it.

I will admit that decaling the launch lug didn't occur to me. :wink:
 

neil_w

Yum yum rockety goodness
TRF Supporter
Joined
Jul 14, 2015
Messages
11,460
Reaction score
4,294
Location
Northern NJ
Now let's play. We'll go back to the rear fins and set the "Repeat" option to "Sticker". This means that exactly one copy of the decal image will be placed on the target, like a, um, sticker. We start here:
dd_test_rear_single.png


Now let's try the X scaling option. By default the scaling values are 1, let's set X to 0.5 instead:
dd_test_rear_stickerx.png

This is pretty straightforward. The decal has been scaled by 0.5 in the X direction. It is pinned to the front/left of the object. Because it is a sticker, there's one copy of the decal and everywhere else shows the background.

Now we can see what the other Repeat options do. Here's "Repeat":
dd_test_rear_repeatx.png

The decal image repeats as many times as necessary to cover the target; in this case exactly two copies are needed because we set the scale to 1/2. This option generally made no difference when the scale values were set to 1, because the single instance of the decal already completely covered the target.

"Repeat and Mirror" does the same thing, but flips alternate copies:
dd_test_rear_double_mirrorx.png

This can be good for making repeating background patterns, if you don't want to do it in the paint program.

Finally, "Clamp Edge Pixels":
dd_test_rear_clampx.png

This is interesting. It shows a single instance, like "Sticker", but now the background is all red. What this option does is fill the background with the edge pixels of the decal image. This is why it is typically the best choice when using a single decal image that completely covers the target: it ensures that the edges are completely covered, and you don't get a bit of background color showing at the edges. So I've modified the first post in this thread to suggest that when using the simplified method described there, always use "Clamp Edge Pixels".

Now let's go back to "Sticker", and try scaling Y instead of X:
dd_test_rear_stickery.png

Pretty easy to understand now, although perhaps a bit surprising that the single image is pinned to the bottom rather than the top. Oh well!

So what happens when we do the same thing to the body tube wrap? Using the "Repeat" option, let's set X scale to 0.2, so we should see 5 copies of the decal in the X direction:
dd_test_bt_repeatx.png

That is a bit surprising. For the body tube, the X axis is around the circumference of the tube, rather than left to right. Oh well #2!

So if we scale Y instead, it'll do this:
dd_test_bt_stickery.png


And here it is with the "Repeat" setting:
dd_test_bt_repeaty.png

Yeah, there's some weirdness here, but once you know what it's doing it's easy enough to deal with.

I didn't show any examples on the middle fins, because they behave exactly like you'd expect. Try it out yourself if you like.
 
Last edited:

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
15,531
Reaction score
2,043
Thanks for taking the time to show us how this works. I've been trying to figure out how the controls work, and I wasn't getting very far.

I've been meaning to try out the nose cone. It looks like it is treated like a tube, but with the front shrunk down, so the decal image is distorted. It would be an interesting challenge to do something useful with it.

I will admit that decaling the launch lug didn't occur to me. :wink:

I was looking at the various missiles that were done by Jesús Manuel Recuenco Andrés in the Open Rocket Design website, and noticed that some of them had details on the nosecone. That's how I learned that it could be done (but not exactly how to use it). The LL trick was something I noticed would be needed if the Estes Wizard's wrap completely wrapped around the body tube and LL.

My first attempt with a nosecone decal was with the Estes Scion.

Now I know how to *fix* my Arapahoe E sims. Look for those to appear in my .ork file thread soon.
 
Last edited:

neil_w

Yum yum rockety goodness
TRF Supporter
Joined
Jul 14, 2015
Messages
11,460
Reaction score
4,294
Location
Northern NJ
Thanks for taking the time to show us how this works. I've been trying to figure out how the controls work, and I wasn't getting very far.
Hope I'm presenting it in a useful fashion.

I think I have two (or maybe three) more posts to go before wrapping up.
 

neil_w

Yum yum rockety goodness
TRF Supporter
Joined
Jul 14, 2015
Messages
11,460
Reaction score
4,294
Location
Northern NJ
Let's say we want to apply our original square image as a "sticker" on the forward (parallelogram) fins. The first thing we'll do is set the scale so it's square. Since those fins have a 2:1 aspect ratio, we'll cut the X scale to half of the Y scale to return it to square:
dd_test_front_sticker1.png

However, the sticker remains pinned to the lower left corner of the bounding box. So let's see what the X and Y offsets do. Set both of them to -0.5 and get this:
dd_test_front_sticker2.png

The first thing to notice is that the negative offsets moved the sticker in a useful direction, to the right (X) and away from the BT (Y). Positive offsets would have moved the sticker in the opposite directions, which are generally not that useful, so *usually* you'll use the negative values. You'll also note that a negative value of X offset moves the decal in the *opposite* direction of a negative offset of a component when building the rocket. Oh well!

Anyway, the value of an offset represents a distance equal to a fraction of the size of the component along that access. So, for X, -0.5 puts the left edge of the decal exactly halfway back on the fin. Likewise, for Y, -0.5 puts the bottom edge of the decal exactly halfway up on the fin.

If we wanted to center the sticker on the fin, we'd have to figure out the right values, either by trial and error or by measurement and calculation. Here's the final result:
dd_test_front_sticker3.png


On to body tubes. Let's set the X scale to 0.5, so the sticker extends exactly halfway around the BT, and Y scale to 0.2, so it's small and manageable (it's *not* a square at this point, though; more precise calculation would be needed to achieve that). Initially it looks like this:

dd_test_bt_sticker1.png

Now let's set X offset to 0.25 and see what happens:
dd_test_bt_sticker2.png

+0.25 has rotated the decal exactly one quarter of the way around the BT, "upwards". So we can guess what -0.25 would do:
dd_test_bt_sticker3.png

This is one instance (the only one?) where positive and negative offsets are potentially equally useful.

Y offsets behave as you would expect; here it is with Y offset = -0.5 (yes, we're back to negatives now):
dd_test_bt_sticker4.png

The decal is moved exactly halfway back on the BT, just like on the fins (although on the fins that was the X axis).

We've now covered everything necessary to do about 99.9% of all decal work you'd want to do. To me, the simple approach described at the beginning of this thread, and the guiding principle of not touching the controls, still looks a lot more inviting than fiddling with the offset and scale controls. But if you ever find yourself needing to adjust something in OR and you just don't want to muck around in the image editor, you know what to do.

Last post in this series will cover rotation.
 
Last edited:

ewg1967

Well-Known Member
Joined
May 26, 2014
Messages
124
Reaction score
0
Really, what I want most from it right now is for it to be stable on the Mac. It's a crazy crash-fest right now.
I've noticed that on my Mac with El Capitan 10.11.3 I can not apply decals at all. It will either render the model as totally black with a black background or either crash. On my old Mac running 10.9.5 I can add decals just fine. Both have the latest version of Java (8 update 73). Very frustrating!
 

neil_w

Yum yum rockety goodness
TRF Supporter
Joined
Jul 14, 2015
Messages
11,460
Reaction score
4,294
Location
Northern NJ
I've noticed that on my Mac with El Capitan 10.11.3 I can not apply decals at all. It will either render the model as totally black with a black background or either crash. On my old Mac running 10.9.5 I can add decals just fine. Both have the latest version of Java (8 update 73). Very frustrating!
I'm on Yosemite still and thankfully haven't had that particular problem... in fact I think I've isolated it (mostly) to one thing: switching from one of the 3D views to a non-3D view (side or back). That is a 100% repeatable crasher for me. So I've worked around it for now by simply never using the 3D views. Instead, I keep a photo studio window open on the side. It's not awesome to work that way but it beats the crashing.
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
15,531
Reaction score
2,043
I've got to say... I've been having some fun with what I've learned from this thread.







Mind you, I'm not done yet, I've got to go teach a lesson so it'll be several hours before I'm ready to upload the new updated file. (Read: I'm all hot and bothered... Why should I be alone?)
 
Last edited:

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
15,531
Reaction score
2,043
Beautiful work as always!
Thanks!

I couldn't have done it without your help! I think I have a pretty good grasp of how decals work in OR now thanks to your efforts.
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
15,531
Reaction score
2,043
Ok, new trick for aligning decals on the body tube in OR.



You might not realize it, but the decals for the Cherokee D were carefully aligned using my MK1 eyeballs. Mind you, the eyeballs haven't been calibrated in some time, and may be out of calibration. However, for the Cherokee D, it's fine.

The decals for the Velociraptor are a different subject.



That fin can decal would likely show it's out of alignment pretty easy, and eyeballing it isn't. So, how to do this and make it look GOOD?

After creating the long diamond shape and applying it to the body tube paint and decal test image I crudely drew Roman numerals ahead of them, and after applying that to the .ork file, I could see how they needed to be adjusted in relationship from each other. If "3" was too close to "1" I could edit the image to move it away from "1". That was all fine and dandy, but verifying the centerline between the fins was a problem. The solution? Fins.

I made a trio of fins that were rotated to be centered between the actual fins. These alignment fins are .001" thick, .25" high, and the full length of the fin can. With those to guide me, I could easily tell if any of the decals were not centered properly.

After I was happy with their locations, I deleted the alignment fins, and the Roman numerals, then saved the file. Sure, I can't zoom in on it and tell 100% if they are exactly centered, but they're a lot closer than they were just using the eyeball method.

HTH
Jim

Oh, and about the Velociraptor. The "VELOCIRAPTOR" decal splits between the O" and the "C" on the actual prototype seen at Tammie's Hobbies in Beaverton, and not between the "C" and the "I" like I have here. The actual widths of the prototype's black and silver bands have yet to be determined, but as there's no painting guide with specific dimensions, it's up to the individual builder to choose how wide they want them.
 
Last edited:

manixFan

Not a rocket scientist
Joined
Feb 15, 2009
Messages
2,004
Reaction score
980
Location
TX
I've noticed that on my Mac with El Capitan 10.11.3 I can not apply decals at all. It will either render the model as totally black with a black background or either crash. On my old Mac running 10.9.5 I can add decals just fine. Both have the latest version of Java (8 update 73). Very frustrating!
See this thread about OR crashing on the Mac:

https://www.rocketryforum.com/showthread.php?133080-Help!-OpenRocket-keeps-quitting-unexpectedly

Great set of instructions in this thread and thanks to everyone else who chipped in.


Tony
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
15,531
Reaction score
2,043
Something I just discovered about fin decals... So you have a fin decal, and it refuses to "sit right", you play with the adjustments for hours, days, weeks... and you still can't get it to ever look right. Something to ask yourself...

Do I have fin tabs? :facepalm:

SURPRISE!!! Those stupid tabs are your problem... Adjust your decal's "height" by the height of the fin tab. Voila! It finally works...

Any guesses on how I discovered this? :facepalm:

In the images below, you can see the difference that factoring in the fin tab can do... The image on the left and fins on the left reflect the correct exposed dimensions of the decal, whereas the right side fins and right side image are what happens when you don't factor the tab in. If you want you can download the .ork file and test it yourself.





While the graphic files for both sets of fins have the same height for the yellow and red bands, the black band was altered to reflect the fin tab.

View attachment Fin Frustration.ork
 
Last edited:

Tobor

Get your peanuts....
TRF Supporter
Joined
Oct 8, 2016
Messages
2,000
Reaction score
601
...Really, what I want most from it right now is for it to be stable on the Mac. It's a crazy crash-fest right now.
Hey Neil, I think I might have two possible solutions to your issue.

First up, VirtualBox (Link). Note: I have quite a bit of "End User" experience with VBox, on Micro$oft hosts. (Dollar sign is an Ode to Redmond's greed)
Basically, you install VBox on your computer (aka "The Host") and use it to run virtual sessions (aka "The Guest") of other OS's. For the Host computer, VBox can run on OS X, Linux, Solaris and M$ Windows.

There are two big caveats in using VBox;
1) You will need an ISO image of the Guest OS.
2) the Host computer must have enough system resources to support both the Host and Guest operating systems. This means multi-core CPU's, a lot of RAM and copious amounts of hard drive space. eg. Installing Win7 requires a minimum of 4 Gigs RAM and 25Gigs HDD/SSD storage, but can run a tad sluggishly with that config.

The other option is Wine (No, not the kind you drink). Wine, now known as WineHQ (Link), creates a compatibility layer and translates Windows API calls into native OS calls in real time. Note: I have only used Wine on Ubuntu and LinuxMint boxes, so I know almost nothing about it's machinations within OS X.

If you are interested in trying VBox, just let me know. I can start a new "How-To" thread of installation and use.
 

neil_w

Yum yum rockety goodness
TRF Supporter
Joined
Jul 14, 2015
Messages
11,460
Reaction score
4,294
Location
Northern NJ
Thanks, but no longer an issue since I learned how to get rid of the 3D view crasher. I have used virtual box but am not a big fan for various reasons.


Sent from my iPad using Rocketry Forum
 

neil_w

Yum yum rockety goodness
TRF Supporter
Joined
Jul 14, 2015
Messages
11,460
Reaction score
4,294
Location
Northern NJ
A follow-up tip on transparency

Normally, I would prefer to apply the base color to the component normally, and then apply a decal image only where the actual decal would be, using transparency as necessary. However, I've found that fades to not look as good when implemented with a transparent decal image.

Look at the following image. In the top sample, the decal is full coverage: a blue fade and white background, covering the entire component. Looks good.

1600270742623.png

In the bottom sample, The decal is just the blue part, fading to transparent, and showing the white body tube underneath. Note how the light part of the fade looks greyish rather than pure blue. I've also found that sometimes (can't seem to reproduce it right now though) the transparent decals will show "edges" where there aren't any, and look bad.

Therefore, I've taken to having my decals be solid color covering the entire component whenever there are fades and such. Looks better in general. Solid stuff with sharp edges like test or roll patterns can work either way.
 
Last edited:

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
311
Reaction score
53
Hi everyone,

I am making a brief post here just as a method of indexing this apparently tremendously useful thread, which I intend to study in detail.

Stanley
 

neil_w

Yum yum rockety goodness
TRF Supporter
Joined
Jul 14, 2015
Messages
11,460
Reaction score
4,294
Location
Northern NJ
Nose Cones and Transitions

Nose Cones and Transitions behave just like body tubes, except... not quite. You're still starting with a rectangular image, but the image is warped to fit the surface. Consider the following decal image:
checkers.png


Here it is, applied to three components: a nose cone, a body tube, and a transition. All have the same length as circumference, so on the body tube the squares stay square:
1615043012398.png


Just by looking, you can see how the image is being warped to shape the surface on the nose cone and transition. This has implications:
  1. The decal image appears in OR differently than if you printed it and applied it to the rocket
  2. Trying to get a particular image to appear undistorted requires that you reverse-distort your image
Item 2 is very hard to describe properly, so I'll just illustrate with a couple of examples.

Here's a transition on Biohazard as rendered in OR. The pinstripes have constant width:
1615043942466.png

To achieve that, I created this decal image:
transition_wrap.png

The ratio of line thickness at top and bottom of the image is equal to the ratio of the top and bottom diameter of the transition. This one was pretty easy.

Nose cones with their compound curves are harder, and I rarely try to get them perfect. Here's the rendered nose cone from Plasma Dart II:
1615044929407.png

Here's the decal image:
pdii_nose_decal.png

Note that in the image, the tapered stripes have straight edges, but when mapped to the curved nose in OR they came out... well, curved. Trying to get them straight on the rendered nose was simply not worth the trouble. As it turned out, I liked the look of the curves, so I made the decals slightly curved. Here's a pic of the finished nose, which ended up pretty close to the OR render:
1615044893792.png

So that's all I can think of to say about noses and transitions. They are a pain in the neck, no doubt about it. Familiarity with more sophisticated paint and/or drawing apps is definitely a plus.
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
15,531
Reaction score
2,043
Here's something for those of you who are interested in metallic finishes... Only works (as is) for round components (nosecones, body tubes) and not things like fins. After applying them, you may need to rotate them (x axis) to get the desired look.

Chrome:
1615527267696.png

Copper:
1615527072184.png


Gold/Brass:
1615527211587.png


Here's a sample of what's possible now...

1615527527164.png
 
Last edited:
Top