Posts Tagged ‘UE4’

City scanner scene – Breakdown pt2

October 13, 2016


This is part 2 of the breakdown for my recent scene Half-Life 2 scanner scene (part 1 here).

This time, I’m going to focus on the Houdini web setup.

Although it took me a while to get a very subtle result in the end, it was a fun continuing learning experience, and I’m sure I’ll re-use a bunch of this stuff!

Go go Gadget webs!

I saw a bunch of really great photos of spider webs in tunnels (which you can find yourself by googling “tunnel cobwebs concrete” :)).

I figured it would be a fun time to take my tunnel into Houdini, and generate a bunch of animated hanging webby things, and bring them back into UE4.

This fun time ended up looking like a seahorse:


I will break this mess a bit 🙂

Web starting points


I import the geometry for the tunnel and rails, and scatter a bunch of points over it, setting their colour to red.

On the right hand side of the seahorse is a set of nodes for creating hanging webs, which is just some straight down line primitives, with a few attributes like noise and thickness added to them.
I’ll come back to these later:


In the top middle of the seahorse, I have a point vop apply two layers of noise to the colour attribute, and also blend the colour out aggressively below the rails, because I only wanted webs in the top half of the tunnel.

The web source points look like this:


From these points, I ray cast out back to the original geometry.

Ray casting straight out of these points would be a little boring, though, so I made another point vop that randomizes the normals a little first:


After this, I have a few nodes that delete most of the points generated from the pipe connections: they have a high vertex density, compared to every other bit of mesh, so when I first ran the thing, I had a thousand webs on the pipe connections.
I also delete really small webs, because they look lame.

We are now at seahorse upper left.

Arcy Strangs.


Not sure what I was thinking when naming this network box, but I’m rolling with it.

So anyway, the ray cast created a “dist” attribute for distance from the point to the ray hit, in the direction of the normal.

So my “copy1” node takes a line primitive, copies it onto the ray points, sets the length of the line to the “dist” attribute (my word, stamping is such a useful tool in Houdini).


Before the copy, I set the vertex red channel from black to red along the length of the line, just for convenience.

Previous up the chain, I found the longest of all the ray casts, and saved it off in a detail attribute. This is very easy to do by just using Attribute Promote, using Maximum as the Promotion Method.

So, I now define a maximum amount of “droop” I want for the webs, a bit of random droop, and then I use those values to move each point of each web down in Y a bit.


I use sample that ramp parameter up there using the web length, and then multiply that over the droop, so that each end of the web remains fastened in place.
And I don’t really care if webs intersect with the rails, because that’s just how I roll…

Fasten your seatbelts, we are entering seahorse spine.

Cross web connecty things


For each of the webs in the previous section, I create some webs bridging between them.
Here’s the network for that.


I use Connect Adjacent Pieces, using Adjacent Pieces from Points, letting the node connect just about everything up.

I use a carve node to cut the spline up, then randomly sort the primitives.

At this point, I decided that I only want two connecting pieces per named web, and I got lazy so I wrote vex for this:

string CurrentGroupName = "";

string PickedPieces[];
int PieceCount[];

int MaxPerPiece = 2;
int success = 0;

addprimattrib(geoself(), "toDelete", 0, "int");

for (int i = 0; i < nprimitives(geoself()); i ++)
    string CurrentName = primattrib(geoself(), "name", i, success);

    int FindIndex = find(PickedPieces, CurrentName);
    if (FindIndex < 0)
        push(PickedPieces, CurrentName);        
        push(PieceCount, 1);
        int CurrentPieceCount = PieceCount[FindIndex];
        if (CurrentPieceCount >= MaxPerPiece)
            setprimattrib(geoself(), "toDelete", i, 1, "set");
            PieceCount[FindIndex] = CurrentPieceCount + 1;
    setprimattrib(geoself(), "name", i, CurrentName);

So that just creates an attribute on a connecting piece called “toDelete”, and you can probably guess what I do with that…

The rest of the network is the same sort of droop calculations I mentioned before.

One thing I haven’t mentioned up to this point, though, is that each web has a “Primitive ID” attribute. This is used to offset the animation on the webs in UE4, and the ID had to get transferred down the chain of webs to make sure they don’t split apart when one web meets another.

At this point, I add a bunch of extra hanging webs off these arcy webs, and here we are:


Then I dump a polywire in, and we’re pretty much good to go!

Well… Ok. There’s the entire seahorse tail section.

For some reason, Polywire didn’t want to generate UVs laid out along the web length.

I ended up using a foreach node on each web, stacking the web sections up vertically in UV space, using a vertex vop, then welding with a threshold:


Since I have the position, 0-1, along the current web, I could use that to shift the UV sections up before welding.

With that done on every web, my UVs look like this:


Which is fine.
When I import the meshes into UE4, I just let the engine pack them.

Seriously, though… These are the sorts of meshes that I really wish I could just bake lighting to vertex colours in UE4 instead of a lightmap.
It would look better, and have saved me lots and lots of pain…

And here we are, swing amount in red vertex channel, primitive offset (id) in green:


Web contact meshes

I wanted to stamp some sort of mesh / decal on the wall underneath the hanging meshes.
If you have a look back at the top of the seahorse, you might notice an OUT_WebHits node which contains all the original ray hits.

I’m not going to break this down completely, but I take the scatter points, bring in the tunnel geometry, and use the scatter points to fracture the tunnel.

I take that, copy point colour onto the mesh, and subdivide it:


Delete all the non red bits, push the mesh out along normals with some noise, polyreduce, done 🙂


I could have done much more interesting things with this, but then life is full of regrets isn’t it?

Back to UE4

So, export all that stuff out, bring it into UE4.

Fun story, first export I did was accidentally over 1 million vertices, and the mesh still rendered in less than half a millisecond on a GeForce 970.
We are living in the future, people.


Most of this material is setting up the swinging animation for the webs, using World Position Offset.

There’s two sets of parameters for everything: One for when the web is “idle”, one for when it is being affected by the Scanner being near it.

To pass the position of the scanner into the material, I have to set up a Dynamic Material Instance, so this is all handled in the web blueprint (which doesn’t do much else).

It also passes in a neutral wind direction for when the webs are idle, which I set from the forward vector of an arrow component, just to make things easy:


So now I have the scanner position, for each vertex in each web I get the distance between it, and the scanner, and use that to lerp between the idle and the “windy” settings.

All of these values are offset by the position id that I put in the green channel, so that not all of the webs are moving at exactly the same time.

Still to come…

Animation approach from Modo to blueprints, lighting rig for the scanner, all the fun stuff! 🙂

Crumbling tiger, hidden canyon

January 9, 2016

In the world of Shangri-La, Far Cry 4, lots of things crumble and dissolve into powder.

For example, my buddy Tiges here:


Or, as Max Scoville hilariously put it, the tiger turns into cocaine… NSFW I guess… That gave me a huge chuckle when I first saw it.

I was not responsible for the lovely powder effects in the game, we had a crack team (see what I did there) of Tricia Penman, Craig Alguire and John Lee for all that fancy stuff.
The VFX were such a huge part of the visuals Shangri-La, the team did an incredible job.

What I needed to work out was a decent enough way of getting the tiger body to dissolve away.
Nothing too fancy, since it happens very quickly for the most part.


I threw together a quick prototype in Unity3d using some of the included library content from Modo:


I’m just using a painted greyscale mask as the alpha, then thresholding through it (like using the Threshold adjustment layer in Photoshop, basically).

There’s a falloff around the edge of the alpha, and I’m applying a scrolling tiled firey texture in that area.

I won’t go into it too much, as it’s a technique as old as time itself, and there are lots of great tutorials out there on how to set it up in Unity / UE4, etc.

As it turns out, there was already some poster burning tech that I could use, and it worked almost exactly the same way, so I didn’t need to do the shader work in the end:

You mentioned canyons?

I actually used World Machine to create the detail in the maps.
In the end, I needed to make about 30 greyscale maps for the dissolving effects on various assets.


I’ll use my Vortigaunt fellow as an example, since I’ve been slack at using him for anything else or finishing him (typical!).

First up, for most of the assets, I painted a very rough greyscale mask in Modo:


Then, I take that into World Machine, and use it as a height map.
And run erosion on it:


I then take the flow map out of World Machine, and back into Photoshop.
Overlay the flow map on top of the original rough greyscale mask, add a bit of noise to it.
With a quick setup in UE4, I have something like this:


Sure, doesn’t look amazing, but for ten minutes work it is what it is 🙂

You could spend more time painting the mask on some of them (which I did for the more important ones), but in the end, you only see it for a few dozen frames, so many of them I left exactly how they are.

Better-er, more automated, etc

Now that I have the Houdini bug, I would probably generate the rough mask in Houdini rather than painting it.


  • Set the colour for the vertices I want the fade to start at
  • Use a solver to spread the values out from these vertices each frame (or do it in texture space, maybe).
  • Give the spread some variation based off the roughness and normals of the surface (maybe).
  • Maybe do the “erosion” stuff in Houdini as well, since it doesn’t really need to be erosion, just some arbitrary added stringy detail.

Again, though, not worth spending too much time on it for such a simple effect.
A better thing to explore would be trying to fill the interior of the objects with some sort of volumetric effect, or some such 🙂
(Which is usually where I’d go talk to a graphics programmer)

Other Examples

I ended up doing this for almost all of the characters, which exception of a few specific ones (SPOILERS), like the giant chicken that you fight.
That one, and a few others, were handled by Nils Meyer and Steve Fabok, from memory.

So aside from those, and my mate Tiges up there, here’s a few other examples.

Bell Chains


Hard to see, but the chain links fade out 1 by 1, starting from the bottom.

This was tricky, because the particular material we were using didn’t support 2 UV channels, and the chain links are all mapped to the same texture space (which makes total sense).

Luckily, the material *did* support changing UV tiling for the Mask vs the other textures.

So we could stack all of the UV shells of the links on top of each other in UV space, like so:


So then the mask fades from 0 –> 1 in V.
In the material, if we had 15 links, then we need to tile V 15 times for Diffuse, Normal, Roughness, etc, leaving the mask texture tiled once.

Edwin Chan was working on the assets for these, and I could have just made him manually set that up in Max, but it would have been a bit of a pain, and I’d already asked him to do all sorts of annoying setup on the prayer wheels…

There were 3-4 different bell chain setups, and each of those had multiple LODs for each platform, so I wrote a Maxscript that would pack all the UVs into the correct range.

Quite a lot of work for such a quick effect, but originally the timing was a lot slower, so at that point it was worth it 🙂

Bow gems


Although I never really got this as on-concept as I would have liked, I’m pretty happy with how these turned out.

Amusingly, the emissive material didn’t support the alpha thresh-holding effect.

So there are two layers of mesh: the glowy one and the non-glowy one.
It’s actually the non-glowy layer that fades out!
The glowy stuff is always there, slightly smaller, hidden below the surface.

Dodgy, but got the job done 😛