Detailed Description

struct A3DGraphMaterialData

Material properties descriptor.

Material properties describes the behaviour of a surface to light emissions, allowing a 3D surface to be represented with realistic responses to light source emissions.



Basic lighting refers to the most standard lighting methods applied within 3D rendering applications, such as with classic OpenGL.

Basic lighting

Basic material properties are:

  • Ambient lighting (m_uiAmbient) is the light an object gives even in the absence of lighting environment.

  • Diffuse lighting (m_uiDiffuse) relies on the surface orientation and light direction. It results in changes across the surface of an object.

  • Specular lighting (m_uiEmissive) simulates the bright effect when a light hits an object and reflects back to the viewer. It relies on the surface and light properties as well ad the viewer’s position.

  • Emissive lighting (m_uiSpecular, m_dShininess) is the light which is emitted by an object, such as a light bulb. When an emissive light is used in a graphics scene, it is treated the same as a light source.

These properties are used within graphical applications to simulate shading, such as with Gouraud or Phong.

Lights are represented using red-green-blue (RGB) color codes. Within A3DGraphMaterialData these colors are indexed into a global state and can be queried using their respective indexes and A3DGlobalGetGraphRgbColorData. The following code retrieves the diffuse color from material, assuming a light gray as default:

A3DGraphRgbColorData rgb_diffuse;
A3D_INITIALIZE_DATA(A3DGraphRgbColorData, rgb_diffuse);
rgb_diffuse.m_dRed = rgb_diffuse.m_dGreen = rgb_diffuse.m_dBlue = 0.75f;
A3DStatus result = A3DGlobalGetGraphRgbColorData(material.m_uiDiffuse, &rgb_diffuse);
assert(result == A3D_SUCCESS || result == A3D_DEFAULT_COLOR);

Most material instances are stored within the global state and identified using an index. It is then possible to retrieve the actual material content by calling A3DGlobalGetGraphMaterialData. Like with any other entity, a material can be associated to metadata known as generic attributes. These attributes can hold any data and extend the capabilities of the associated A3DGraphMaterialData instance. For example, physically-based rendering is implemented in HOOPS using generic attriutes. To obtain these attributes, use A3DMiscPointerFromIndexGet instead which returns the underlying A3DSDKRootEntity instance.

// Retrieves the underlying entity of a globally stored material object using
// its index `i`.
A3DEntity* material_handle = 0;
A3DStatus result = A3DMiscPointerFromIndexGet(i, kA3DTypeGraphMaterial, &material_handle);
assert(result == A3D_SUCCESS);
assert(material_handle != 0);

A3DRootBaseData root_base;
A3D_INITIALIZE_DATA(A3DRootBaseData, root_base)
result = A3DRootBaseGet(material_handle, &root_base);
assert(result == A3D_SUCCESS);
Then the generic attributes can be browsed from the A3DRootBaseData instance.
Alpha component

Colors within HOOPS Exchange are three-components codes using A3DGraphRgbColorData (red, green and blue). Most graphics implementations use a fourth component, alpha, which is typically used to hold per-channel transparency information. If you are interesed in transparency at material level, check out the m_ucTransparency member in A3DGraphStyleData. A3DGraphMaterialData stores the additional alpha channels in separate A3DDouble members. As for color channels, they range from 0.0 to 1.0.

Material Attributes

Public Members

A3DUns32 m_uiAmbient

The global index for the Ambient light.

A3DUns32 m_uiDiffuse

The global index for the Diffuse light.

A3DUns32 m_uiEmissive

The global index for the Emissive light.

A3DUns32 m_uiSpecular

The global index for the Specular light.

A3DDouble m_dAmbientAlpha

An additional alpha channel for ambient ligthing.

A3DDouble m_dDiffuseAlpha

An additional alpha channel for diffuse ligthing.

A3DDouble m_dEmissiveAlpha

An additional alpha channel for emissive ligthing.

A3DDouble m_dSpecularAlpha

An additional alpha channel for specular ligthing.

A3DDouble m_dShininess

The shininess value. For example, usual values may range into 0.0 (no shininess), 5.0 (low) or 100.0 (high).