The mental ray Arch (architectural) & Design material improves the image quality of architectural renderings. It improves workflow and performance in general, and performance for glossy surfaces (such as floors) in particular.
Special features of the Arch & Design material include self-illumination, advanced options for reflectivity and transparency, ambient occlusion settings, and the ability to round off sharp corners and edges as a rendering effect.
A range of material effects available with the Arch & Design material
For a variety of suggestions on using the material to create specific effects, see Arch & Design Material (mental ray): Tips and Tricks.
What Is the Arch & Design Material?
The mental ray Arch & Design material is a monolithic material shader designed to support most materials used in architectural and product-design renderings. It supports most hard-surface materials such as metal, wood, and glass. It is especially tuned for fast glossy reflections and refractions.
The major features are:
- Easy to use, yet flexible: Controls are arranged logically in a most-used-first fashion.
- Templates: Allow fast access to settings combinations for common materials.
- Physically accurate: The material is energy conserving, making it impossible to create shaders that break the laws of physics.
- Glossy performance: Advanced performance boosts including interpolation, emulated glossiness, and importance sampling.
- Tweakable BRDF (bidirectional reflectance distribution function): You can define how reflectivity depends on angle.
- Transparency: “Solid” or “thin” materials: Transparent objects such as glass can be treated as either solid (refracting, built out of multiple faces) or thin (nonrefracting, can use single faces).
- Round corners: Simulate fillets to allow sharp edges to still catch the light in a realistic fashion.
- Indirect Illumination control: Set the final gather accuracy or indirect illumination level on a per-material basis.
- Oren-Nayar diffuse: Allows “powdery” surfaces such as clay.
- Built-in Ambient Occlusion: For contact shadows and enhancing small details.
- All-in-one shader: Photon and shadow shader built in.
- Waxed floors, frosted glass, and brushed metals: All fast and easy to set up.
Physics and the Display
The Arch & Design material attempts to be physically accurate, so its output has a high dynamic range. How visually pleasing the material looks depends on how colors inside the renderer are mapped to colors displayed on the screen.
When rendering with the Arch & Design material, it is highly recommended that you operate through a tone mapper (exposure control) such as the mr Photographic Exposure Control in conjunction with Gamma and LUT Preferences; or at the very least, use gamma correction.
A Note on Gamma
Describing all the details of gamma correction is beyond the scope of this topic; this is just a brief overview.
The color space of a normal, off-the-shelf computer screen is not linear. The color with RGB value 200 200 200 is not twice as bright as a color with RGB value 100 100 100, as one might expect.
This is not a bug. Because our eyes see light in a nonlinear way, the former color is actually perceived to be about twice as bright as the latter. This makes the color space of a normal computer screen roughly uniform, perceptually. This is a good thing, and is actually the main reason 24-bit color (with only 8 bits or 256 discrete levels for each of the red, green, and blue components) looks as good as it does to our eyes.
The problem is that physically correct computer graphics operates in a true linear color space where a value represents actual light energy. If one simply maps the range of colors output to the renderer naively to the 0–255 range of each RGB color component, the result is incorrect.
The solution is to introduce a mapping of some sort. One of these mapping methods is called gamma correction.
Most computer screens have a gamma of about 2.2 (known as the sRGB color space). Lower gamma-correction values tend to make everything look too dark, especially midtones. The light does not “add up” correctly.
Using a gamma of 2.2, the theoretically correct value, makes the physically linear light inside the renderer appear in a correct linear manner on screen.
However, because the response of photographic film isn’t linear either, some users find that this theoretically correct value looks too bright and washed out. A common compromise is to render to the gamma value of 1.8, making renderings look more like photographs: That is, as if the image had been shot on photographic film and then developed. However, for best results when you export and import images (such as texture maps) to and from an external image-editing program, set all Gamma values on Preferences 
Gamma and LUT Preferences to 2.2.
Exposure Control (Tone Mapping)
Another method for mapping the physical energies inside the renderer to visually pleasing pixel values is known as exposure control or tone mapping. You can accomplish this either by rendering to a floating-point file format and using external software, or with a plug-in that allows the renderer to do it on the fly. In 3ds Max such plug-ins are known as exposure controls and are accessed from the Environment dialog.
Use Final Gathering and Global Illumination
The Arch & Design material is designed to be used in a realistic lighting environment: one that incorporates full direct and indirect illumination.
mental ray provides two basic methods for generating indirect light: Final Gathering and Global Illumination. For best results, be sure to use at least one of these methods.
At the very least, enable Final Gathering, or for best-quality results, use Final Gathering combined with Global Illumination (photons). Performance tips for using Final Gather and Global Illumination can be found here.
If you use an environment for your reflections, make sure the same environment (or a blurred copy of it) is used to light the scene through Final Gathering. To accomplish this in 3ds Max, include a Skylight in your scene and set it to Use Scene Environment, or use Daylight system with Skylight set to mr Sky.
Use Physically Correct Lights
Traditional computer-graphics light sources live in a cartoon universe where the intensity of the light doesn’t change with the distance. The real world doesn’t agree with that simplification. Light decays when leaving a light source, due to the fact that light rays diverge from their source and the intensity of the light changes over distance. This decay of a point light source is 1/d 2 ; in other words, light intensity is proportional to the inverse of the square of the distance to the source.
One of the reasons for this traditional oversimplification is that in the early days of computer graphics, tone mapping was not used, and problems of colors blowing out to white in undesirable ways was rampant. (Raw clipping in sRGB color space is displeasing to the eye, especially if one color channel clips earlier than the others do. Tone mapping generally solves this by “soft clipping” in a more suitable color space than sRGB.)
However, as long as only Final Gathering (FG) is used as indirect illumination method, such traditional simplifications still work. Even light sources with no decay still create reasonable renderings. This is because FG is concerned only with the transport of light from one surface to the next, not with the transport of light from the light source to the surface.
It’s when you work with Global Illumination (GI) (that is, with photons) that troubles arise.
When GI is enabled, light sources shoot photons. For the Arch & Design material (or any other mental ray material) to be able to work properly, it is imperative that the energy of these photons match the direct light cast by that same light. And since photons model light in a physical manner, decay is built in.
Hence, when using GI:
- Light sources must emit photons at the correct energy.
- The direct light must decay in a physically correct way to match the decay of the photons.
Therefore it is important to make sure the light shader and the photon emission shader of the lights work well together.
In 3ds Max, this is most easily solved by using photometric lights. All of these lights are guaranteed to have their photon energy in sync with their direct light. It is built in and automatic, and you don’t need to worry about setting it up.
Performance Features
The Arch & Design material contains a large set of built-in functions for optimal performance, including but not limited to:
- Advanced importance sampling with ray rejection thresholds
- Adaptive glossy sample count
- Interpolated glossy reflection/refraction with detail enhancements
- Ultra-fast emulated glossy reflections (Highlights+FG Only mode)
- The option to ignore internal reflections for glass objects
- The choice between traditional transparent shadows (suitable for objects such as window panes) and refractive caustics (suitable for solid glass objects), on a per-material basis.
Procedures
To create a physically correct, self-illuminated surface:
- Create your geometry and obtain or create a photometric file of the luminaire. Determine the lamp color and intensity, as measured or provided by the manufacturer; for example: 1,500 cd/m 2 and 3,700 degrees Kelvin. Enable exposure control and global illumination.
- Create a photometric light (the halogen lamp) and set its color and intensity.
- Turn off the light source’s Affect Specular property.
- Create and place the light-shade geometry and apply an Arch & Design material to it.
- On the Self Illumination (Glow) rollout, set the same color and intensity you applied to the light source. Also, turn off the Illuminates The Scene (When Using FG) checkbox in the Glow Options group.
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Render the scene.
An example of this application is a realistic halogen pendant luminaire with a translucent shade, such as frosted glass.