Simulate a Ghost Rider transformation

Rss Bot · October 4, 2017

Ghost Rider shone as one of the new characters in Marvel's Agents of SHIELD. When Ghost Rider appears you know there are going to be some really cool Ghost Rider transformation scenes, where you'll see a living breathing dude turn into a fiery skeleton.

There are some interesting things that happen when Ghost Rider transforms and we'll be breaking all of them down in the same way as his skin changes: piece by piece.

22 mighty Maya tutorials to try today

The first thing that happens is that his skin starts to boil. You can see bubbles appearing, in a similar way to when you heat some plastic. Then, the skin starts to break off in patches; it's really interesting to see these cracks as they start appearing. Eventually, the skin starts flying off, thanks to environmental factors like wind. From below, his skull starts showing but there's a very neat and sort of controlled chaos in the way his skin cracks.

Let's take a look at how we can achieve these effects using Maya and a spot of After Effects.

You can download the files for this tutorial here. And to view images at a larger size, simply hit the expand icon in the top-right corner of the image.

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01. Prepare the footage

Try to use a tripod when you shoot your footage...

Before we jump into a 3D program – Autodesk's Maya, in this case – it's worth preparing for the shot. You need to capture good footage. The display is up to you but make sure you stabilise the footage or shoot it on a tripod. Get some sudden movements from the actor as well as slow ones, for when the fire is inside the character's head and burning him when he's human, before slowly turning into the Rider.

02. Stabilise the footage

...otherwise, stabilise it afterwards

If you don't happen to have a tripod to shoot on, it isn't the end of the world. There are some useful compositing tricks that you can use in order to stabilise the footage. First of all, import your footage into Adobe After Effects, create a new composition, drag the footage into this composition and then right-click on the footage in the timeline.

You'll see a Warp Stabilizer VFX button appear. Click it, and then in the properties of the effect, simply change Smooth Motion to No Motion. Do this only if your footage is suffering from camera shake.

03. Sort the geometry

Find a pair of models to match your footage

You'll need two models. First, a human base to simulate. This won't contribute to the final composite but it's what we'll burn. Second is the skeleton. Get both of these models, fit the skull inside the head as well as you can and clean the geometry. Weed out any holes. In Maya's modeling module, go to Mesh in the toolbar and find Reduce. This helps cut poly from the geometry.

04. Skinning geometry

Create some joints to match your model, then skin it

Make some joints based on the actor model and skin it. In my case, I only have the head, and only a small portion of the head. So I created three joints. One from the chest to the neck or the bottom of the skull, another from the neck all the way to the top of the head and a third one that doesn't really do anything but I like to have in case I need changes later.

05. Animate the geometry

Animate your geometry so that it matches the movement in your footage

Now, animate the geometry to move like the actor in the footage. Get this as close as possible. Once done, create a copy of those animated joints using Edit> Duplicate Special (in the settings of that, check the Duplicate Input Graph to copy the animation) and skin this new joint system to the skull for a quick and accurate duplication of the actor model's motion.

06. Turn geometry into nCloth and rigid bodies

You don't want your skin going through your skull

Under the FX module in Maya, go over to the nCloth menu bar and then click Create nCloth while selecting the actor model. This will transform your actor model into an nCloth on which simulations can then be made. In the same menu bar, you'll find the Create Passive Collider option. Click this button while selecting the skeleton model in order to turn it into a Rigid Body. By doing this, you can ensure that the skin on the actor model will be prevented from going through the skull.

07. Prepare for the maps

Now you're going to need some animated maps

You'll need between two and three animated grayscale maps for this part of the tutorial. Firstly, you're going to need a simple map, which goes from total white to total black – let's call this one Dynamics Map. Secondly, you'll need another map that goes from total white to having some black patches but not total blackness – we're going to call this one Tearing Map. The third map you'll need is a copy of the Tearing Map. You just need to invert the colours, offset it by a few frames and then multiply it to the original, getting the edges of the animation.

08. Dynamics map

The dynamics map dictates how much of your mesh is nCloth

This map will control how much of your mesh is actually nCloth and how much of it isn't. Essentially, if the map is all white, no vertex on your mesh will be dynamically simulated as nCloth. This is very important if your mesh is deforming. In my case, I made some dark areas appear in the map as the actor was moving to make it more natural. You can use the Fractal Noise in After Effects to generate this.

09. Tearing map

The tearing map controls how skin breaks off

This map decides where the skin starts to break off from. Black areas will break off completely, meaning every single vertex in that area will separate. Create this like a fabric with white and black patches. Try to minimise the blackness but don't completely eradicate it. I'd say a number near 20 per cent is good. Copy this map and invert its colours. Multiply this new map with the original to create a third map. This will be used to generate sparks.

10. Input mesh attract

Setting Input Attract Mesh to 1 disables nCloth simulation on the mesh

Usually when you turn a mesh into nCloth, you lose the animation. However, there's a setting under the nClothShape node's Dynamic Properties tab called Input Attract Mesh. Set it to 1, which disables nCloth simulation on the mesh and follows the deformation caused by the rigging. In the next tab, input the Dynamics Map into the Input Attract Map to multiply the attribute with your map.

11. Tear the skin

Use the Tearable Surface setting with the tearing map

Select the actor model and under the FX module, go to the nConstraint menu. Click the Tearable Surface button. Your surface will tear like skin. Among the newly created nodes, find one called nComponent and under the Glue Strength Map, input the Tearing Map. This way, your cloth will become weakly bonded and patches of skin will start falling or flying, depending on your settings.

12. Tweak the environment

The Turbulence button will add variety to your animation

Now that the skin is breaking, make some changes to the environment. Create some wind under the Nucleus node. Under the nClothShape's Dynamic Properties tab, decrease the mass to something like 0.1 or so. The number depends on the scale of your scene. Finally, select the actor model, go to the Fields/Solvers menu bar and click the Turbulence button to add a turbulence field to create some really nice variation in how the skin flies. Without this, the cloth doesn't look good.

13. nCaching the dynamics

Cache nObject to stop it resimulating all the time

In the nClothShape, find the Caching tab. Change Cacheable Attributes to Dynamic State. Go to the nCache under the FX module and go to Create New Cache (you might have to first click Enable all Cache on Selected) and select nObject. Let it cache for a moment. This will save you having to resimulate every time you change the frame.

14. Light the eyes

Use a V-Ray Sphere Light to light up the eyes

Now we need some fire in the eyes. One method would be to play with materials and self-illumination but that's too much work. Simply go ahead and create a V-Ray Sphere Light. Fit it into one of the eyes. Now, having already selected it, go to the Edit menu and access the Duplicate Special's settings by clicking the square next to it. Check the Duplicate Input Graph and Instance Leaf Nodes. The copy will now be able to take on the attributes of the first light.

15. Create FumeFX node

Brush up on your FumeFX skills for this bit

You'll need some basic knowledge of FumeFX. Save a copy at this point. Hide the actor model if you want, to speed things up. Go to the FumeFX menu and click FumeFX Node. Go to the Node's attributes and play with Width, Height and Length to better fit the skeleton mesh, basically, a rough location where the fire lights up. Spacing is the resolution of the simulation.

Next page: Create sparks, render your different elements, and finish off the model

16. Feed the fire source

Time to set your skeleton on fire

With the skeleton model selected, go the FumeFX menu and pick the Object Source button. Now your skeleton model lights on fire. Run initial simulation by going into the Attribute Editor for the FumeFX node, click the button that's blue-ish and looks like a server rack, select your source from there and then click on the Play button.

17. Animate the fire rate

Adjust the attributes to get your fire looking just right

You have to decide which frame the fire starts to show up and how fast. Also, I would suggest some smoke before the actual fire appears. You have to change two settings for that. First, in the FumeFX node under the Output tab, change Start Frame to whatever you want. Select your source object and animate attributes like Fuel, Smoke, Oxygen and Temperature to set exactly how and when the fire starts, and simulate again.

18. Create sparks

Generate some sparks using your third map

Using the third map, we'll generate sparks to show some fire flying out. Select the actor model (ideally a version without nCloth simulations) and go to the nParticles menu. Click on Emit from Object. Once done, change the Emitter Type in the Emitter node to Surface. Go all the way to the bottom and in Texture Rate, input the third map and check Enable Texture Rate.

19. Sparks material

Play with the intensity until you hit a setting that goes with your exposure

Create a new V-Ray Mtl Material or a V-Ray Light Material through the Hypershade. Change the colour to light orange and play with the intensity – find a setting that works with your exposure settings, if making a Light Material. If you're making a V-ray Mtl Material, turn on the Self-Illumination slider and set the colour to orange. Select the nParticle node and apply the material to it.

20. A texturing problem

Things don't always go right first time

Now, I got into a problem with texturing that I think would be helpful to discuss for a bit here. You might not run into this particular sticky situation if you did some pre-planning, which is actually something that I did, but unfortunately it got lost over the four-month period that it took me to do this. Anyway, the problem is that I used Spherical Projection before I created the maps but I wanted to put a planar map as the diffuse for my actor model. That's a problem.

21. Planar material mapping

Here's how to project an image without messing up UVs

If you want to project an image on a mesh without having to mess with the UVs, create a new material. In the diffuse channel (or any other) import a texture. Select File from the Texture Creator, right-click and pick Create as Projection. Now, you can project your image without messing up the UVs. Once placed, delete history or you can bake your texture into the current UVs.

22. Baking the map (optional)

Use Convert to File Texture to bake your map, if you want

Simply go to the Hypershade, select the Material as well as the mesh and just go into the Edit menu and click Convert to File Texture. This will turn your projection image into a usable separate material and distort it according to your UVs rather than distort the UVs to fit your projection. If that happens, it will throw everything you have done up to this point away and you'll have no choice but to redraw the maps and everything else we have done.

23. Render the skull

Render all the elements in separate files

I'd suggest you render everything in different files. Render the skull as it is. You can also use the V-Ray Material in Render Element, which basically just outputs the objects with the selected material into a separate file. Although it doesn't get you the Alpha map for those specific materials, so you'll have to keep that in mind. Use this for the skull only. The skin is a different story…

24. Render the skin

You only need to render skin that's currently breaking

To composite skin on top of your footage, create a third map. What you basically need is to only render out the part that's breaking at any given moment. Stuff that's not yet broken shouldn't be visible. You can use some modified version of the Tearing Map for this. Honestly, I can't think of any other way you can do this, so maps are all you've got!

25. Render the fire

Render the fire using Render Elements

Since you've already got skull and skin, you'll just need to subtract them from a beauty pass for the fire. Render it using Render Elements as well, it's good to have things in separate files so you can edit them later if you want. Now one thing, the rendering is actually very very resource-heavy due to the cloth simulation. nCache helps a bit but not by much, so you have to consider that.

26. Compositing

Put everything together in After Effects and you're done

Compositing is a subjective action. You need to think about what you want from the effect and then you have to composite it to your taste. One thing I would recommend, though, is adding some glow. In After Effects, go to Effects, locate the Glow option and then add it to the overall scene using an adjustment layer. Another thing that would be nice is to add some motion blur to the scene. Go to Effects and find Pixel Motion Blur to force some blur to be added to the scene.

This article originally appeared in 3D World issue 225; buy it here!

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