We will start with the material for the windows. There are various types of glass such as that of a magnifying glass, a simple window pane or frosted glass. Its look is primarily defined by its Transparency and Reflectance settings. Cinema 4D automatically adds transparency as soon as the Transparency channel is enabled in the Material Editor. A special * Transparency * layer will be added to the Reflectance tab. More about this later. Generally speaking, the Transparency value should never be set to its maximum of 100%. Doing so would create a perfectly transparent material, which is basically never the case in reality. Slightly reducing the transparency of the glass also lets us add shadow in conjunction with the Color channel’s settings. However, since our glass has no special coating or color we will disable the Color channel completely. This will create a black base color for the material. Since the degree of transparency is defined by the Brightness value in the Transparency tab’s Color settings, we will use a pure white with a Brightness value of 90%. This ensures that the glass will remain visible even in front of a pure white background and will also cast a slight shadow because light will not pass through it entirely unhindered.
The Refraction value must also be adjusted to make the glass look realistic. The default value of 1.0 corresponds to that of air. This can be used for very thin objects such as a transparent film but for thicker objects, a more realistic value should be used. Various charts with the most common refraction values for transparent materials can be found online as well as in the Cinema 4D documentation and in the Material Editor. Two of the most common values are 1.333 for water and the media value of 1.6 for glass. As you can see, these values only differ slightly. Most transparent materials have refraction values between 1.0 and 2.0. We will not use the default values for our material and use a Refraction value of 1.6 instead. To achieve a realistic effect, the transparent object must have volume. For our car glass this volume would be the double-sided model. Otherwise the car could end up looking like it’s filled with water when you look through the windows. For our glass material, set the Refraction value to 1.01.
Reflections and highlights
The Total Internal Reflection and Exit Reflections options are enabled by default. The Total Internal Reflection automatically supplements a reflection on a material and can be seen primarily at the edge of the preview sphere in the Material Editor. This shows that this reflection is controlled by a Fresnel effect. The Fresnel Reflectivity can be used to control the degree of reflection where the surface curves away from the viewer’s angle of view. The Fresnel effect is common for reflections and should generally remain enabled. The Exit Reflections effect on the other hand also calculates a reflection between an object’s outer edges. This makes it possible for a reflection on an object’s front side to reappear on the back side, albeit to a lesser degree. When applied to thin-walled objects, this can lead to somewhat irritating slightly offset double reflections. This is physically correct but can still cause irritation. We will disable this effect for our comparatively thin window.
Since our windows will be neither colored nor weathered, no other settings have to be modified in the Transparency channel and we can switch to the Reflectance channel’s settings.
We already mentioned that almost no material is completely transparent that has reflective properties. This is why the * Transparency * layer is automatically added to the Reflectance channel when the Transparency channel is enabled. This special layer only offers basic settings for adjusting the degree of reflection and highlights. The intensity is automatically controlled by the Fresnel effect defined in the Transparency channel. Therefore, reflections and highlights will be most apparent where the surface curves away from the viewer’s angle of view. Since our glass will have a smooth surface, we will leave the Roughness value at 0%. The Bump Strength setting will have no effect in our case because our material contains no Normal or Bump textures.
This concludes the description of how to create a basic glass material. Assigning the material to objects is also comparatively simple because the material does not contain any textures, which means we don’t have to take any type of projection, scale or positioning into consideration. Simply drag the material from the Material Manager onto the Window Subdivision Surface object in the Object Manager. The same material can also be assigned to the glass on the front and rear lights (Headlight and Backlight Glass). These objects are located in the Lights object group in the Object Manager. Simply drag the material onto the objects in the Viewport or in the Object Manager to assign them to the objects.
Turn signals and bulbs
To add a little variety, the turn signals and bulbs will be assigned a different, much more reflective transparent material. The basic setup is the same as with the window texture. We will also disable the Color channel here and set the Transparency channel’s Refraction value to 1.3 (the same applies here as above, i.e., that you should use a refraction value of 1.01 to achieve a realistic result for the glass. However, since the objects’ volume is not as large as the car’s interior, this effect won’t be quite so obvious).
We will again disable the Exit Reflections option but this time reduce the Brightness value to 70%. This will automatically strengthen the reflections on the surface and the material will appear darker overall. Please refer to the image below for all other settings:
A new Specular - Standard layer will be created for each new material and will produce a matte highlight without reflection by default. These default settings are not suited for smooth, hard surfaces such as glass. Therefore we will use this layer to strengthen the reflection on the glass. Click on Layers and rename Specular - Standard layer to Reflection. The settings in the image below can be used:
The Reflectance channel’s * Transparency * layer’s settings remain almost unchanged. If needed, you can also add a Beckmann, GGX, Ward or Phong, etc. * Transparency * layer to increase the degree of reflection or highlight. Please refer to the image below for all other settings.
Materials can be easily applied to objects via drag & drop from the Material Manager or by dragging an object from the Object Manager into the respective material’s Assignment field in the Assign tab’s menu. Assign the turn signal and bulb materials to the Indicator Glass and Bulb objects, respectively, in the Lights object group in the Object Manager.