Basic Materials (Arnold)

Introduction

In this lab, we will be learning about the basic materials in Arnold (Maya’s default render engine). Specifically, we will be exploring the aiStandardSurface shader in order to make PBR, or realistic, materials.

aiStandardSurface vs. OpenPBR

As of Maya 2027, the default shader is OpenPBR, a physically-based shader made in collaboration between Autodesk and Adobe for the purpose of creating an industry standard shader.

For the purposes of this lab, we are using aiStandardSurface, the default shader for the Arnold Renderer. However, you are free to use OpenPBR for your own group project.

This lab is split into the following 2 parts.

1. Uniform Materials
2. UV Unwrapping and Texture Mapping

TODO: Read Me!

Throughout the lab, you will see callouts such as this instructing you to perform a task related to what you need to submit on Gradescope, such as taking screenshots or exporting files.

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Shading and Texturing Review

As a review on some terminology, a shader is a network of attributes and textures. These attributes link together and tell the renderer how your mesh reacts to light. This defines the material of your mesh.

A material is a set of qualities defining the look and feel of an entire object. For example, metal, plastic, orange juice are all examples of a material. What isn’t a material is something like an image, bump map, or any type of texture.

Please refer to the lecture slides if you’re confused about the difference between a shader, material, and a texture.

In today’s lab, we will be using both materials and textures together to explore how they interact with each other!

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An Introduction to Materials

Please download and unzip the following lab file to get started.

Download ArnoldUniformMaterials.zip

Materials and shaders as a whole are unique to each render engine. For example, aiStandardSurface is unique to and only works with Arnold. Other render engines have their own equivalents, like Pixar Renderman’s pxrSurface.

Info

There are however, certain shaders that are ubiquitous enough to work with any render engine. One such shader is the lambert shader. In fact, the lambert shader is the default shading material assigned to all meshes once created! (As of Maya 2027, this has been replaced with the OpenPBR shader.)

Some other shaders that are equally as ubiquitous as the lambert shader are the blinn and phong shaders. The reason why these ones are so widely supported by every render engine is due to them being one of the first and most simple shaders to be created!

The aiStandardSurface

First, let’s add a cube and give it the aiStandardSurface shader! Hold right click over the mesh until a dropdown appears. Then select Assign New Material → Hypershade.

A popup box should now appear. Here, shaders are categorized by their shading engine. What we’re interested are the shaders under the Arnold tab. Go there and then select the aiStandardSurface shader.

Anything that begins with ai means it is an Arnold shader. For example, aiToon is the Arnold toon shader. To make sure you’re using Arnold compatible shaders, make sure your shader begins with ai.

Woo! You’ve now created your first material! You can view this in rendered mode by clicking the little Arnold logo on the top of the viewport. In rendered mode, you can see how the shaded cube looks with lighting. Make sure you turn this off when you’re editing settings as it can lag your computer a lot.

Though you might notice that it’s not too terribly interesting at the moment. To make it more interesting, we have the tweak various parameters in the Attribute Editor! If you go to the Attribute Editor and scroll through the tabs to find the aiStandardSurface1 shader, you can see all the attributes related to the shader that you can tweak!

The first thing you should do is rename your shader to something more descriptive than aiStandardSurface1. This is incredibly important! Otherwise, when working in a big project, you might have a shader called aiStandardSurface24 and have no idea what it refers to. You can see that I’ve renamed it Cube_Shader here.

Before we get into what each attribute does, let’s start by applying some presets. Clicking the presets tab on the upper right, you can see a bunch of different shading presets that are available. In this class, we encourage you to make the entire shader yourself to learn what each attribute does, but if you want, you can use these presets to get a feel for how to achieve certain effects.

You can click the Replace button to replace the entire shader with the preset, or you can blend what you currently have with a percentage of the new shader!

Here is a cube of honey!

Rendering

Make sure to view your shaded objects in rendered mode! Lighting plays a huge role in what the final product looks like!

aiStandardSurface attributes

I won’t go over every single one of the aiStandardSurface attributes, but I will list a few key ones to note here:

Attribute	Settings
Base	Weight - Controls how much of the base diffuse color is contributed Color - Controls the color of the diffuse Metalness - Controls how metallic the diffuse is
Specular	Weight - Controls the strength/presence of reflections Color - Controls what color reflections on the object are Roughness - Controls how rough the surface is. A lower value means more shiny, while a higher value means more matte IOR - Index of Refraction for glasslike objects or liquids that bend light
Transmission	Weight - Controls how transparent an object is
Subsurface	Weight - Controls how translucent an object is SubSurface Color - Controls the color of translucence

Check Your Understanding

Please refer to the lecture slides if you are confused about parts of this shader or what certain terms mean. Additionally, you can go to the Arnold Shader documentation if you are curious to learn more about the properties of the aiStandardSurface shader!

TODO: Gummy Material ( gummy_bear_screenshot)

Play around with the aiStandardSurface settings to see if you can recreate this material here as best as you can. Some helpful hints are to think about what this material is made of. Is it a dielectric or a conductor (metal or non-metal). Is it reflective? Is it rough? Is it transparent? Is it transluscent?

Once you recreate the material, view it in rendered mode and take a screenshot of the cube with the gummy shader applied. Name this screenshot gummy_bear_screenshot.png.

UV Unwrapping and Texturing

UV Unwrapping

Next, let’s assign a texture to our objects! As a reminder, textures are 2d images that you assign to materials to give more flexibility in the way they look. Today we’ll go over assigning UV Editing and assigning texture maps. Please download and open this lab template.

Download ArnoldUVUnwrap.zip

You should see a pencil mesh sitting on top of a plane. The aiStandardSurface has not been assigned to the pencil yet, so please assign it and name it something descriptive.

Let’s start by going into the UV Editing workspace. On the upper right corner of Maya, change the workspace to UV Editing.

You should now see the UV Editor next to your viewport. Then, go to object mode and select the pencil. To create some default UVs for our pencil first, in the UV Editor, go to Create → Camera-based. We can’t unwrap UVs unless we have them. That’s why it’s important to always create default UVs to work with.

You should now see a wireframe of your pencil appear in the UV Editor. Currently, all our UVs are overlapping on top of each other which is not good. We need to mark edges as seams to “unfold” our object. Think of it like peeling a tangerine - we need to take off the peel and flatten into a two-dimensional shape, so we need to cut the peel at certain points (mark seams) and then take the peel off and flatten it out (unfold).

To mark seams on your object, go into edge mode and select edges, then go to the UV editor and click Cut/Sew → Cut. (Hotkey is Shift X while your mouse is hovered over the UV Editor). Remember that you can double-click an edge to select the whole edge loop, and shift + click to select multiple edges at once. Additionally, shift + double-click selects all edges between the first selection and the second selection.

Before we start unwrapping, let’s think a bit about how we would unfold this pencil. The thing to keep in mind is that you want your seams to be at deliminating portions of the mesh. For example, breaking down this pencil into its material components, we might want to separate the metal eraser cap, the body of the pencil, and the exposed wooden tip of the pencil, and the graphite lead portion of it.
Separating these out into multiple parts would allow us to easily differentiate between different key sections of our object. When creating seams, we want seams to be in places that are hidden or not easily visible. You wouldn’t want your T-Shirt to have a seam down the middle of your torso would you?

Additionally, since our pencil is cylindrical, we want to mark an edge running down the entire cylinder as a seam to “unfold” the cylinder. You can’t unfold a cylinder otherwise! If you want to visualize this in real life, try to unfold a cylinder without making any cuts.

Once you finish marking your seams, your pencil should look something like this.

Now to unfold the map. Save your work (as this can sometimes crash Maya), then select your whole object and click Modify → Unfold. Make sure you have your pencil selected in object mode. You can also easily access these tools in the UV Toolkit on the side.

Each section of the pencil surrounded by seams has been unwrapped.

Now, in the UV Editor, you can hold right-click and and select by UV Shell. You can now use your w, e, r hotkeys to move, rotate, and scale these shells around to position them around.

To make life a bit easier, we want to our shells to be in the 0-1 UV square. There are a couple tools that we can use to organize our UV shells. Selecting all your shells, you can use Modify → Layout to automatically layout your shells. Additionally, tools like Modify → Orient Shells can help align your shells properly.

Hover over the different “shells” to figure out which shells belongs to which part of the object. This will be important very soon! Mine looks like this.

With any UV Unwrapping process, we need to make sure that our UVs are not distorted. There are a few ways to view this.

You want to click these two buttons here at the top of your UV Editor Panel. This will place a checkerboard pattern across your UV Tiles and display them on your mesh. You can then see how a texture gets tiled across your surface.

We can also go to Image → UV Distortion to view the UV Distortion on our mesh.

The key important things to notice here are the colors. Our mesh should be mostly white, which means there is little to no distortion. Blue means the texture is compressed while red means the texture is stretched. When UV Unwrapping, we want to minimize as much distortion as possible.

Overall, we did a pretty good job.

Another thing to note is the direction of your UVs. You can see here in the eraser that the UVs are actually swirling around the eraser. Although this is not a problem with our current mesh, this can pose issues for other textures you might have that are dependant on the direction of the UVs. For example, a wooden plank goes in a single direction, however if your UVs are slanted or swirly, then your texture will also be slanted/swirly.

An important thing to note is that your UVs don’t have infinite resolution. In order words, the larger your shells, the more pixels we are able to allocate to that specific UV region. This is known as texel density. In order to get more detail on specific shells, we need to make the shells larger so they take up more space in the UV editor, which in turn will allow more texels/pixels to be inside each shell.

You also don’t want your shells to be too close to each other or the edges of your UV tile to avoid any issues where the colors might bleed into each other. You can do this by going to the option box for the Layout tool (Modify → Layout option box).

Understanding these concepts is key to UV Unwrapping properly.

Texturing

Now we want to export our map and import it into photoshop or another image editor, to paint on top of it. In the UV editor, click Image → UV Snapshot. Then, hit Browse next to the filename and choose an easy-to-find location. Change the format to PNG, and keep the rest of the settings.

TODO: Pencil UV Map ( pencil_uv_map)

Please rename the exported UV map to pencil_uv_map.png. You can do this by changing the Filename before exporting or by renaming it after exporting.

Now, open up this file it outputs in an image editor of your choice. I will be using Photoshop (free for Berkeley students), but you can use anything you want. Feel free to use Krita, Procreate, FireAlpaca, or even MS Paint!. This is the fun part - painting on the details. Create a new layer underneath the UV map, and color it black. This way, we can see our UV seams on top and also have some contrast on the bottom. Make sure to name these layers so you don’t accidentally modify them.

Now we can see our UV map. Since we know which UV shell corresponds to each part of our mesh, we can color them accordingly. Paint on the black layer to give your shells some color. Here, I have colored the pencil yellow with a tan wooden part pink eraser, and gray ferrule and tip.

Here, I encourage you to add more detail than what I have added here. For example, some simple shading to the pencil, scratch marks, a rough wooden texture to the wooden tip, etc.

Now, hide the layer with the UV map in it, and export your image to the folder template that was given (IE: where your scene is located). Now, let’s create a metal-ness (metallic) map, to make the metallic parts of the pencil shiny! This will really make it more realistic.

Warning

If you do not hide your UV seams when you export your final image, those UV seams will show up in your final texture!

Un-hide your UV map layer and Un-hide your black layer. Now, we want to color over where our ferrule is and make it metallic. This will be a grayscale image. The more white your color is, the more metallic it will be. The more black your color is, the more non-metallic it will be. That means we should make the shell that corresponds to the ferrule white, and the rest of the image black (since it’s not metallic). You can also make the tip gray since it’s made of graphite. Here’s what I made:

Like before, hide the UV map layer and export your image. Your image should be located inside the lab folder, ArnoldUVUnwrap, that was given.

TODO: Pencil Textures ( pencil_color and pencil_metal)

Make sure to move both texture files (the color and metal map) into the ArnoldUVUnwrap folder. Rename the color texture to pencil_color.png and the metal texture to pencil_metal.png.

Applying Your Textures

Now, let’s connect these textures to our object’s shader! First, let’s switch back to the default, General, workspace in the upper right corner dropdown.

Select your pencil and add the aiStandardSurface shader if you haven’t yet already.

Next, we want to open up the Hypershade editor. Go to Windows → Rendering Editors → Hypershade.

You should see something like this

To view the graph network of your shader, go to the Materials section and find the shader that you wish to edit. In this case, it is the shader that I attached to the pencil.

Hold right click and go to Graph Network.

You should then see your shader network appear in the graph.

I would also recommend naming your shader to something more descriptive.

You can pan around by holding middle mouse + drag. Additionally, you can zoom in and out using the scroll wheel, and just like in your viewport, f will focus on whatever you have selected.

Remember from lecture that a node is a unit of information. Here, we want to connect some information that the pencil shader is going to use to control its base color.

To do this, hover over somewhere in your graph and click tab. This will allow you to type in the name of the node you want to use. If you do not know the name of the node you want to use, you can always select it from the list of all shaders on the left hand side.

We want to create the file [Texture] node.

If we select the file1 node we just created and go to the attribute editor, we can attach the texture we just created the Image Name attribute.

Then, by selecting the little green dot next to Out Color in the file node, we can drag that over to the Base Color attribute in the pencil shader.

This will then connect our file texture to the Base Color. In other words, the Base Color of the shader is whatever is connected to it. The thing that’s connected to it, is this file texture.

I’m also going to rename this file node to “diffuse” since that’s what I called my texture file.

Next, let’s connect our metallic map. To do this, create a new file texture node and assign it the metallic map file you created earlier.

Notice how you cannot drag the Out Color into the Metalness attribute in the pencil shader.

The reason for this is because the Out Color is 3 values, the red, green, and blue channel. However, the metalness attribute is only a singular value (also known as a float). It is simple a single number saying how metal an object is, not 3 different numbers telling you how much red, green, and blue they are.

So then, how do we use our metallic map if our metallic map outputs a color? This is how data textures work. By using only black and white, our red, green, and blue channels are all the same. We can just interpret this as a singular gray value that says, the more white it is, the higher the metallic number, the more black it is, the lower the metallic number.

If we click the + button next to the Out Color, we can expand it into its individual R, G, and B channels, which are each singular values. Remember that a gray color has all R, G, and B all the same value, so it doesn’t matter which one you use.

Here, I can drag one of these channels into the Metalness attribute in our pencil shader.

Important

Due to the way color spaces work, for data textures such as this metallic map (and other maps such as specular roughness maps, etc), we need to make sure we’re not doing any color conversion to this texture. To do this, we need to set our Color Space to Raw which will tell Maya to not use any color conversions on this file, and to instead just use the raw associated value.

If you did everything correctly and do a test render, it should look like this! Notice how only the ferrule is metallic.

TODO: Textured Pencil Screenshot ( pencil_screenshot)

Take a screenshot of this and make sure you are showcasing and angle that makes your metallic map visible. Rename the screenshot to pencil_screenshot.png. You will be required to submit this.

In order for us to grade your work, you’ll also need to archive the scene with your pencil. This will create a ZIP file that preserves everything in the scene, including textures, so that we can see what your textures look like on our end.

TODO: Archived Pencil Scene ( ArnoldUVUnwrap.zip)

Inside of the pencil Maya file, go to File → Archive Scene. This creates a .zip file wherever the pencil file is saved. Locate the file and rename it to ArnoldUVUnwrap.zip.

Trying it out on your own & Triplanar Projection!

Go to the following website here. Polyhaven is an amazing website that has many materials available for you to use! Pick an interesting material and download its associated texture maps. Make sure the file format you’re downloading is ZIP.

Additionally, click the three lines next to the right of the Download button and make sure the following are checked.

Go back to the ArnoldBasicLabTemplate from earlier. The one with the nice fancy dome light and the cube you experimented on. Delete the cube and instead make a default gear. You can do this by going to Create → Polygon Primitives → Gear.

Try to connect your diffuse texture into the base color.

You notice here how bad UVs on the side cause the texture to stretch really badly. This is really annoying, especially for environment models where UV unwrapping might be more tedious than helpful. Here, we will employ something called triplanar projection to solve this.

Triplanar projection allows us to “project” the texture uniformly onto the surface instead of relying on UVs. Essentially, we can place a texture on an object without needing UVs, allowing us to texture things efficiently. This is incredibly useful for uniform materials. If you are confused, refer back to the lecture slides.

We can create an aiTriplanar node and connect our textures like this instead. Essentially, we take our texture, plug it into a triplanar projection, and then plug the triplanar projection into the base color.

Analyzing it backwards, our base color is driven by a projection, and that projection is projecting the file texture we’ve inputted.

If it’s difficult to understand how nodes connect together, it’s okay! It’s hard, but understanding these effectively will be really helpful.

Notice how our texture is now uniformly projected and how there’s no more UV stretching!

Next, connect the rest of your textures. Remember, data textures (so roughness maps, etc. Anything that’s not related to the color of the final output) need to have its color space set to raw.

Don’t forget to plug each texture into its own triplanar projection node.

For your normal map, plug your file into an aiNormalMap node, and plug the outValue of the normal map node into the Normal Camera attribute. Remember, normal maps are data textures so make sure to set your color space to raw.

For your displacement map, create a displacementShader node. It will come with a blue displacementShader1SG node but you can delete that.

To apply your displacement map, plug your displacement texture (remember it’s data texture) into your displacementShader’s Displacement attribute. Then connect the output of your displacementShader to the Displacement Shader attribute in your aiStandardSurface1SG node.

In your displacementShader node, you can adjust the Scale attribute in your attribute editor to adjust how strong the displacement map is. I generally find that a scale of 0.1 is sufficient.

Don’t forget all all your textures should go through an aiTriplanar node before plugging in anywhere.

If you’ve done it correctly, then you should get something like this

TODO: Gear Screenshot ( gear_screenshot)

Take a screenshot of this. Rename it to gear_screenshot.png. You will need to submit this for your homework.

Wrap Up & Submission

Textures and texture maps can go a long way! Textures can represent colors, but they also represent data points. For example, I can use a texture to control the transmission of an object to make certain parts transparent, or use a texture map to add artificial bumpiness with bump or normal maps!

If you’re interested in more advanced shading, understanding how it works more in depth and creating procedual textures, please check out the Hypershade Editor lab (note that this uses a different render engine, Renderman. Talk to a facilitator if you don’t know how to install it)!

If you followed all the TODOs throughout the lab, you should have all the deliverables needed to submit to Gradescope. For a refresher on what is required for this lab:

Screenshots (.png)	Textures (.png)	Lab Files
gummy_bear_screenshot	pencil_uv_map	ArnoldUVUnwrap.zip
pencil_screenshot	pencil_color
gear_screenshot	pencil_metal