Javelin missile launcher

[chilly crag]

I think it would be cool to have a realistic Javelin missile launcher in the game.

I do not know how to do the lock-on and projectile animations and custom particle effects.

The real-world Javelins lock onto a target or point, ejects the missile out, then the missile fires straight up into the sky and flies down onto the locked location/target.
How difficult would this implementation be?

[chilly crag]

I managed to get the projectile to go up and then follow any actor that has a specific tag. The issue now is I cannot figure out ray-casting.
My plan is to create an empty actor with the relevant tag at the ray-cast hit of where the player is aiming, but I am having issues with implementing ray-casting

[graceful willow]

loving the arm break when reloading! 😂

[chilly crag]

It's using the RPG-7's reloading animation, so it's a little busted 😆

[soft wave]

Looks amazing! I'm sure you have resource material but you could try delay the rocket ignition and speed up the rocket by about 50-75% on its downwards ark.

[vagrant spear]

Hey you did it! What sort of trouble are you having with the ray cast exactly?

Also I'm curious do you have an ADS?

[slim elk]

Hey, I would love to help in making the missile behave more "realistically". What FGM-148 Javelin launcher variation is it and what is the name of the primary missile fired in your showcase?

Also your trajectory should look more like this than a Parabola.

[chilly crag]

I'd have to delay the projectile_movement component. I'm not 100% sure how yet

[chilly crag]

I think I figured out the raycast issue

[chilly crag]

I'm working on trying to get a working scope for the javelin

[chilly crag]

I'm not sure of the variation. I just loved the one used in Battlefield and CODMW, the one that locks on, ejects the missile, launches upward, and then strikes the locked target from above.

[chilly crag]

Interesting. Could you elaborate a bit?

[vagrant spear]

Huzzah!

[slim elk]

Sorry, Figure 4 is what the motion of the missile should look like, with height of the missile on the Y-axis and range on the X-axis. Without making it overly complex and simulating the flight path, you could just draw this graph with Bezier curves and then scale it up based on distance. This would also allow for the iconic deployment look of the FGM-148 Javelin launcher.

[chilly crag]

Ok, cool. Not sure how to do that, but I'll consider it. Thanks

[slim elk]

How are you currently doing the trajectories.

[chilly crag]

Honestly, the projectile velocity is doing most of the work. I just force the projectile upwards for a few seconds before acquiring the target and then moving towards it

[slim elk]

Also, here is a really good video of a showcase of the screen and controls of the FGM-148 Javelin launcher: https://www.youtube.com/watch?v=plrYVkZsWp4

[chilly crag]

Cool. Thanks. If I get the scope to actually work, I'll use this as reference of how the screen UI must look

[slim elk]

Great!

[chilly crag]

Current state of project:
Struggling to get the scope of the javelin to look right. Something with the material color is giving me problems.
(See images)

Future concerns:

1. I use the player character blueprint for the lock-on system, which I am worried will give the lock-on functionality to any player from any faction.
2. Ray-casting sometimes hits the player and doesn't lock-on at the range you always want. (I think the ray-cast is bound to the player and hits anything in front at ground level)
3. Animations (I am not good with making custom animations)
4. Usability by bots (I have no idea if bots will be able to use the javelin, due to requiring a lock-on first)
5. The same actor is used as the lock-on object, which means that all players' lock-ons might confuse the projectiles, if there are too many on the map.

[vagrant spear]

Is the crosshair image on a transparent background

[chilly crag]

Yes. I used the chroma key in UE4 to make the material background invisible. This same method worked with UI materials I made for screens

[vagrant spear]

Hmmm that is curious how it ended up like that

[placid meadow]

@chilly crag, I think I have a little something for you! 🎁

[chilly crag]

That looks very nice. How did you do it?

[placid meadow]

👀 You'll see

[vagrant spear]

👀

[past patio]

awsome guys

[chilly crag]

Well thanks for just boasting about your achievement on my mod project channel 😂

[proud crow]

What vehicle mod you using?

[placid meadow]

https://drive.google.com/file/d/1JkGD6F3oz8K_T24ltNitWd7XC4tnHabc/view?usp=sharing

FGM148_Mod_Source.zip

Just drop in the same folder next to your mod and you can see how I did everything in the test map

This includes just enough for you to get started on the overylay, I made all of the elements by hand, but you're free to use them.

The thermal post process material instance, in MaterialLibrary/MI_FLIR_FGM148, is applied to the scope weapon, but that's a child of the old scope weapon so you should just use the new scope component and apply the post process material there.

Overlay WBP, textures, and audio are all included

BP_HDPlayerCharacter_ATGM is necessary to set these properties on the character meshes, that's the only modification necessary to make in character though

The thermal material uses custom stencil value as a the base temperature value, and applies others parts of the buffer to make it look more realistic

[placid meadow]

In the material instance you can set the Resolution Y value to a higher value if you don't like the pixelated effect as much, or you can disable the Use FLIR Resolution option altogether, but I think it adds a lot of realism

There is also a Use FLIR Color Gradient, instead of a simple color this use a texture gradient (included) as a look-up table

You can also use the 3Color option and set a 3 color gradient

[placid meadow]

White hot / black hot polarity

Primary FLIR controls for gain / contrast

[chilly crag]

Cool, thanks so much @placid meadow

[placid meadow]

Just one sec, update to fix a few things in the FLIR material

Made a few parameter changes to make things less confusing 😄

Okay, there you go
https://drive.google.com/file/d/1JkGD6F3oz8K_T24ltNitWd7XC4tnHabc/view?usp=share_link

Feel free to ping me any time if you have questions

[chilly crag]

Thanks so much. I'll have a look at it when I get a chance

[past patio]

this is awsome

you guys are so good at this

will you guys release this as a source code or a packaged mod?

[chilly crag]

I want to release it as a mod, but the devs can then freely use and implement it in the base game.

There are still a number of issues to sort out before this weapon can work in a game, especially in PvP

[chilly crag]

I stated the issues here 👆

[placid meadow]

2. Ray-casting sometimes hits the player and doesn't lock-on at the range you always want. (I think the ray-cast is bound to the player and hits anything in front at ground level)

What are you using this for specifically? Line of sight check?

If it is for line of sight from the launcher to the target, use this instead

This is a very consistent function

For performance I do something like this

First check if distance is within some threshold (very cheap)
Check if player is on screen even if they are occluded (fairly cheap)
Light of sight check (more expensive, but very accurate)

Is On Screen function

[chilly crag]

Thanks. I'll look into this, because I think I am doing the raycast wrong, by using the player object/actor as starting point. The lock-on currently doesn't properly lock where you aim, it just draws a straight line along the ground until it hits anything

[placid meadow]

Yeah, for both the lock-on by the launcher and the missile line of sight check will work better

You can modify the Is On Screen function to check if the actor is within a smaller area on screen, so a lock-on box basically, if it is within that area then you check line of sight

For the missile I might do an off angle check from the missile's forward vector

That is, if you plan to simulate the seeker at all

[chilly crag]

I'll get to that later, maybe 😅

[placid meadow]

Did you already implement a DIRECT / TOP attack mode select?

[chilly crag]

Another main issue I worry about is the lock-on method when other players/bots are in-game with Javelins. I currently spawn an actor with a specific tag, and that's how the projectile knows where to go. The issue is that I need to separate everyone's actors so their missiles only fly to their own actors...

[chilly crag]

I see this as a "bells-and-whistles" item, so not yet 😅

[placid meadow]

Don't use tag, you should pass a reference of the target actor to the missile / projectile

Your concern is absolutely valid, it will get the first actor index with that tag, and tags have other issues

So when you spawn the target, just pass the actor object to a custom event on the Projectile, something like SetTarget(Actor)

Then, when the Projectile initializes On BeginPlay, it should just check if target is set yet, as it won't be for a few miliseconds

The Javelin actually doesn't seek until after the boost / climb phase anyway, so you'll only need the target after motor burnout

[chilly crag]

I should add that I spawn a prefab that contains the actor. I couldn't find a SpawnActor method

[placid meadow]

Search for "Spawn Actor From Class", then in the class select Actor or a custom actor

If you want to track a moving target, you should attack Actor to Target Actor

[sacred furnace]

Would most likely be cleaner to have the var exposed if you're spawning the actor when setting the target ref

[chilly crag]

Ah ok, can't believe I missed that

[placid meadow]

After attaching your actor to the target actor, you can get the actor bounds origin and set world location so that the actor the projectile is locked on to hits the center of the target, not the origin which could technically be anywhere

If you check Only Colliding Components, than it will calculate the bound from active collision meshes only, this could be useful if there was some component that made the actual bounds much bigger

Now your missile should be able to lock on to a moving target's center of collision bounds

Then you just pass the reference to the projectile via a custom event, which will happen after it has initialized anyway, and that function will set its own target variable

In your seeker you would probably have to use a line trace by channel (visibility) with complex collision enabled, tracing from the missile seeker to the target

That is again if you want to be able to break lock or any such functionality

[chilly crag]

That's pretty useful, thanks. Will work especially well with vehicles later

[placid meadow]

Depending on speed though you would have to lead the target's velocity vector, so it gets complicated fast

[placid meadow]

I would say that even for a fairly basic implementation of the Javelin this will be necessary. Being able to select between DIRECT / TOP attack is fairly fundamental.

TOP attack has a much lower minimum range limit, because of the climb phase of the flight profile, it is used against armor at a considerable distance away.

DIRECT still climbs, but much less so and can arm the warhead and hit a much closer target

[placid meadow]

I think the most difficult aspect of this will be for bots but there might be a nice work around to make it work like indirect fire mode, instead of a RPG which is essentially a ballistic projectile

Something cool about the NLAW, it only fires in DIRECT mode, where it does not have a passive seeker at all, but tries to fly a perfectly straight line to the aim point, and has a magnetic fuse to detonate over the target

This is why the NLAW does not need TOP attack mode to kill armor, because the warhead flies over and the shaped charge is aimed down

Crazy weapons, but for the FGM-148, DIRECT / TOP attack modes are essential

[past patio]

NLAW has a pretty complex inertial guidance tho

to make it realistic of course

[placid meadow]

Absolutely. In games you can basically set gravity to very low just add a little up/down/left/right random movement during flight, which simplifies it

Javelin is a beast to simulate 😄

(exp: 8+ years in military simulation 😅)

[past patio]

yeah javelin is fucked up

the tricky thing I see in modelling the NLAW 100% correctly is that the inertial navigation fir the NLAW can be set to follow a angoular velocity for a moving target

but idk if that is actually hard or not to model as I am a mod noob

[placid meadow]

Constant angle rate guidance isn't too hard

[past patio]

even when that angle rate has to be picked on the spot based on the movement of the sight?

[placid meadow]

Yep, not hard if you don't fully simulate the missile as an aerodynamic projectile, once you add aerodynamics everything gets hard though

Most games just simulate missiles as basic kinematic objects, no actual physics

[past patio]

yeah fair

not very much added value in that much level of modelling especially for such weapons

[unique grotto]

@visual ice

[visual ice]

Nice 😄

[chilly crag]

This is a bit complex for me to figure out how to use it in my setup. I might need some guidance or an explanation, please 😬 . This is my current ray-cast setup to spawn the prefab where your character is looking. You will probably see the flaw (the fact that it is raycasting from the character itself)

And this is what makes the projectile lock on and fly upwards

I'm still a bit new to blueprint logic, sorry

[visual ice]

Does it account for a moving target?

Pretty nice. I've often thought you just need to use splines to make missile locking reliable

[chilly crag]

No, this is very basic.
It's basically: When projectile is spawned, fly up for X seconds, then find actor with tag "Homing" and fly to it.

It MIGHT work on a moving target, but it may not be very accurate or effective

[visual ice]

Bonus points if it homes in on where it thinks the vehicle WILL be 😄

[slim elk]

No offence to Jantakobi but understanding Polynomials(Quadratic, Cubic and Quartic) enough to write your own solution for them is a long and daunting task.

[slim elk]

Quadratics is easy. However Quartics are an absolute beast to solve with very few solutions/resources on the internet.

[placid meadow]

I don't know, I absolutely suck at math and was able to implement a quartic solver to calculate the ballistic trajectory for intercepts between two moving objects. I can't stress enough how bad I am at math. 😄

@chilly crag Bluedrake said your Javelin will support direct and top attack modes in a video, so now you have to implement it! 🤣

[chilly crag]

And it sounded like he gave ME credit for the thermal scope screen, and that it is already implemented. Sorry about that 😂

[visual ice]

Proportional Navigation (pronav) algorithm is more realistic and "easier"

The missile just tries to keep you in the same area of its view

[slim elk]

My solution that I made a few years ago was based on an "optimized" quartic solver a research paper implemented, from 2010. It was backed up by fairly good accuracy and numerical stability. What resources did you use and what solution did you implement, I would love to have a look?

[slim elk]

Yea, that seems like the way to go.

[visual ice]

You can't be that bad at math if you have the tolerance to even copy someone else's implementation for a quartic solver lmao

Quartic equation, for anyone curious

not a joke^

I think it's also expensive to calculate. At least every frame/tick

You don't need the mathematically perfect aim orientation. But I get the desire for it

Battlefield does "pure pursuit"

which is basic bitch missile tech

[slim elk]

The analytical algorithm for efficiently solving Quartics looks a lot closer to the below images. However, the stability of the below solution is unknown.

[slim elk]

However, complexity depends on the accuracy and stability of the solver. Most can't be implemented with just a basic understanding of mathematics.

[chilly crag]

It kind of almost does work with a moving target 😶

[placid meadow]

You absolutely would not implement are quartic solver for missile guidance in a game, that's the wrong solution to begin with

Pure pursuit would be for a SAM, while a ATGM could use a fairly simple PID loop with simple lead estimation only if the target velocity vector is above some minimum threshold

The key for Javelin will be the flight profile, which consists of climb, glide, terminal phases, where the angle of each is defined by the attack mode

Climb phases is unguided, while glide and terminal are guided but with different PIDs

[past patio]

absolutely correct

SAMs needs to take an interception path becouse they need to deal with much higher velocities

[placid meadow]

Terminal needs different PIDs than glide because as the missile closes distance with the target any amount of off angle will increase exponentially. Glide PIDs are tuned for low anglular deviation, while terminal PIDs are tuned for high angular deviation.

[chilly crag]

But won't this target-interception only be required for high-speed targets, such as jets?

[placid meadow]

Still required for a moving vehicle, it just needs to lead the target though, nothing like actual missile guidance

[placid meadow]

@chilly crag are you still working on this? Let me know if you're stuck or something

[chilly crag]

@placid meadow I got stuck at this point and I'm not proficient enough with blueprints to figure out what you suggested. I also don't have enough time to work on the project now

[placid meadow]

Ah no worries, if you don't mind sharing your files someone else might be interested in picking up where you left off 🙂