Trash Bag

Goals

My main goal was to achieve realistic-looking materials with interesting details to explore. So here I come up with an idea to make a translucent trash bag.

Software

• 3ds Max
• Marvelous Designer
• ZBrush
• Marmoset Toolbag
• Photoshop
• Substance Painter

References

I didn’t follow any specific references, mostly I was improvising and experimenting along the way.

Preparing for Simulation

First I modeled generic trash such as cans, bottles, boxes and etc. It can be whatever you want to see in your trash bag. Just make sure that you have enough polygons on your models because later all this trash is going to be imported into Marvelous Designer, as we know Marvelous can’t simulate properly if your meshes are too low poly, so keep that in mind. Once we are done with modeling you can unwrap and texture it as you like.

Next, we need to collect all our trash together into an interesting shape. I modeled a basic shape out of the box to make this process faster by applying a Noise modifier and FFD 4x4x4 in 3ds max. I used trash texture which I found on Google and then edited it in Photoshop to make it seamless.

Then I covered the basic shape with my trash.

Simulation

Now it is time to import our trash into Marvelous Designer. I just created 2 rectangle sheets sewn to each other with top edges set to Elastic. And Particle Distance is set to 2, note that very low values gonna take longer to simulate, so you can start your simulation with 10, then once you are happy with the shape you can lower it to 2 or 3. You can also make a knot in Marvelous Designer but it is tricky and might be a very time-consuming process. So I decided to sculpt the knot in Zbrush because it is faster and easier.

Here are my settings for Physical Property. You can play around with values till you get the best result suiting your preference. So I exported this simulation in FBX format to use it later as my high poly for baking.

You can do a low poly version of your bag right here, just simply increasing the Particle Distance value. For me 45 was good enough, the lower numbers you put – the more detailed geometry you will get.

Sculpting

You can import your bag from marvelous into Zbrush to understand better what kind of size and shape you want for the knot. I sculpted this knot using only Standard and Dam Standard brushes.

High to Low

Back to 3ds max to edit low poly from Marvelous Designer for a better match with high poly. Keep in mind that the bag, knot, and all trash inside the bag – are separate meshes. So I named all the parts to make it easier to bake in Marmoset Toolbag.

Uving

Nothing extraordinary about UV here. In game production, it would be too expensive to have 2k textures just for one trash bag model (if it is not a trash bag simulator game lol). It would be more reasonable to unwrap all the trash-related props in one UV set.

Baking

Here is the trick, I baked two versions: the first one is only a plastic bag with the knot, and the second is just a trash with no bag. For the plastic bag, I baked all the required maps to work on later in Substance Painter.

And for trash, I baked only Height, AO, and Albedo. Don’t worry if you have distortions like on my screenshot, after mixing in Photoshop it will be covered by our Height mask.

Textures

To make a translucency effect I used previously baked Albedo of trash and created a mask using a Height map.

Then I played around with mask contrast and brightness.

I decided to use all my baked maps such as AO, Height, and Curvature with different blending modes and opacity. So my diffuse texture was fully done in Photoshop.

I imported all my baked maps into Substance Painter to make roughness map with a different mixture of grunge maps, and add some extra tiny details such as wrinkles and dots on plastic bag.

Rendering and lighting

We are back to Marmoset Toolbag for rendering. As you can see from my screenshots that my scene is very simple. For sure you can always make it more complex and use dozens of lights, but I like to keep my scenes simple as they would look in the game, so 3-4 light sources seem enough to me. My goal was to get a feeling of night street, and I guess it turned out well.

That’s it! We are done here. Hope that my tricks were useful and inspiring for you. Thanks to Games Artist for giving me the opportunity to write this article! Have great success!