Koru Materials

Materials in Koru are made of layers. Exactly as in your favorite graphics editor, Koru lets you specify some layers and then renders them one on top of another to display the shape on screen.

Main Parameters

Besides layers each material also has Main parameters block that contains material–wide parameters:

Main parameters of materials in Koru

The Double–sided option controls if the material is visible from both sides of the shape, or just from its front. Here are two similar shapes, where the left one has double-sided material, while the right one has a single side:

Single- and double-sided materials in Koru

Note that the shapes are the same, but you don’t see the inner part of the right one. That’s because it has single–sided material that is visible only from its front.


Each material in Koru may have several layers:

Layered material in Koru

Here you see a material with 3 layers named “Top Layer”, “Middle Layer” and “Bottom Layer”. The top one is currently selected and you see its properties at the right. As you may see, layers have Mask and Bump parameters that work layer–wide, and also three optional blocks: diffuse, emissive and specular. You can read more about these blocks using the links at the left.

When Koru needs to render a shape it gets its material and renders the shape with each of layer from the bottom to top. For the material on the picture above, Koru first renders the shape using “Bottom Layer” parameters, then renders it again with “Middle Layer” parameters and finally renders it with “Top Layer” parameters. As the top layer is opaque green, you don’t see any lower layers on the shape, but if it was transparent or had a mask, you would see the underlying layers on the shape.

Here we have the same material, but the checkers mask is loaded into the top layer’s mask slot:

Layer mask in Koru

Koru uses the mask to reveal the middle (gray) layer where the mask is black and keep the top (green) layer where the mask is white.

Rendering a single layer

When you enable both diffuse, emissive and specular blocks in the same layer, Koru has to define which goes first. Here’s what it does:

  1. First of all it renders diffuse block, of course if it is enabled;
  2. Then it renders emissive block, again if it is there;
  3. The last comes specular block, also if it is there.

This means that if you have a highly–reflective specular block enabled, you may not see diffuse and emissive blocks behind it even if they are enabled. Consider using multiple layers or layer masks to display something on top of the reflective areas, or to reveal the lower layers.

Do I need multiple layers?

In most cases one layer is enough. You can define the base color with diffuse block, add some reflections with the specular one and get a nice–looking material.

However, some materials need more layers. For instance, lacquered aluminium needs two reflections: one for the aluminium itself and another for the lacquered layer. Another case is a complex material having some base texture and another one on top of that applied with a mask: partially rusted surface, for instance.

In such cases you need to create several layers and provide masks or control their transparency to make sure that all underlying layers are visible.

Diffuse Layers

Diffuse layers in Koru have two properties: color and opacity. You can load a texture into color slot, or just use the color:

Simple orange diffuse material in Koru

If you load a texture to Color slot, the image will be multiplied by the tint color:

Tinted orange texture in diffuse material in Koru

The screenshot above displays the default built–in “ipad–screen” texture loaded to Color slot and tinted with the orange color.


The Opacity control lets you make diffuse layer semi–transparent. The lower its value, the more you see through the layer. Let’s remove the texture from the color slot and set opacity to 90:

90% opaque material in Koru

Now let’s change it further to 30:

30% opaque material in Koru

As you see, the lower numbers you use, the more transparent becomes the layer.

This is the simplest transparency in Koru and it works fine for thin objects like paper, where you don’t need to simulate refraction.

Emissive Layers

Emissive layer block is pretty simple, as the diffuse one:

Emissive layer block in Koru

It lets you specify the light color and its intensity. Koru use these parameters when it computes the scene glow effect. Any reflected highlight or emissive layer block adds to the glow effect.

Below is a scene of three balls. The left one has simple diffuse gray material, the middle one has emissive block enabled and the right one has emissive block with checkers texture to control the emissive areas.

Comparison of emissive materials in Koru

You see the left ball doesn’t glow at all, the middle one has even glow, while the right one has more glow on its bright areas.

Specular Layers

Specular layers are all about reflections. If you need a material to reflect something, you need to enable the specular block in its layers. There are two common usage cases for specular layers: add reflection to something opaque, or make glass–like materials. Both are explained below, as well as the thin–film interference effect which is also supported.

Reflective Opaque Materials

This works for paints, plastics, metals and other types of materials where you have a base color or texture and some reflection on top of that. Here’s how it is done in Koru:

Simple reflective material in Koru

You see that the layer has both diffuse and specular blocks enabled. Diffuse block defines the base orange color of the material, while the specular block controls the reflection. The most important parameter here is N — the index of refraction, that controls how much light will be reflected (and refracted) by that layer. Set it to 1 to avoid reflection and refraction, use higher values to get reflection.

Here is the same material with N = 3:

More reflective material in Koru

You see that our material becomes much more reflective. To make a metallic reflection, you need to switch IOR selector to “Complex” and increase the value of K parameters which controls the metallic reflection:

Metallic material in Koru

It now looks like a painted metal. Further increasing of both N and K values gives you a very reflective metallic material:

A very metallic material in Koru

You can add another layer to make another reflective layer on top of this one. Add a layer and enable specular block there. Make sure the layer is added above the current one:

Two-layers material in Koru

Here we set that new layer to have specular block only, then we configured it to be orange and to have N of 1.5, so only edges are reflective. This second layer adds another orange reflection on top of the main metallic one. Have a look at lacquered alluminium materials in Koru materials library to see more examples of this effect.

Reflective Translucent Materials

Another common usage of specular block is making glass materials. In that case you usually don’t need the diffuse block enabled, just the specular one. Here is a simple example:

Simple translucent reflective material in Koru

Note that the shape is barely visible. The reason is that all you see at the moment is reflections, and as the N is 1.5 (like plastic or water), you don’t really see a thing. It looks like a soap bubble without those color effects (see below). In order to make it more realistic, we need to tell Koru to simulate refraction, so the material refracts the scene behind. You can do so by increasing the Refraction Level parameter. Let’s set it to 10:

Refractive translucent material in Koru

Now that’s glass. You can tint it up using Transmission parameter, that controls the light going through the layer:

Green refractive glass material in Koru

That’s how you make colored glass in Koru. You can make a “frosted glass” effect by increasing the roughness level:

Frost green refractive glass material in Koru

Exactly as with opaque materials, you can have several specular layers to make a more complex material. Use mask and transmission parameters to control the light coming through the layers.

Thin–film Interference

That’s that rainbow–like effect you may see on soap bubbles, oil spots or metals. Koru simulates it pretty well, but you need to specify some wavelengths… No worries, it is not that difficult. Let’s start with a metallic material that we made above:

Another very metallic material in Koru

Now check the Thin–film Interference box below the specular block and see the difference:

Thin-film interference in Koru

Koru added a thin (200 micro–meters) film with the index of refraction of 1.5 and simulated light interference there. Adjust the width to see different colors, here we set it to 250 micro–meters:

Another thin-film interference in Koru

Best of all, you can load a texture controlling the thickness in different areas. Here we loaded a built–in noise texture:

Texture-controlled thin-film interference in Koru

Play with the thickness levels, controlling texture and N/K values in this block to get the effect you need. It may take time to master that, but it is worth it.

That’s All!

Have a look at other Koru tutorials we have: