geom/doc/salome/gui/GEOM/input/material.doc

/*!

\page material_page Material properties

\tableofcontents

\section material_general_description General description

\note The functionality related to the material properties is
\b experimental, so it might work not as expected. The behaviour might
be changed in the future versions of SALOME Geometry module.

\n You can change the material properties of the selected shape(s) in
the dedicated dialog box. This dialog box can be invoked from the
context popup menu using "Material properties" item:

\image html material.png

In this dialog box you can:
- modify the properties of the material model currenly assigned to the
shape presentation;
- assign one of predefined global materials to the shape;
- create a custom material model and apply it to the shape.

\note This functionality is available in both OCC and VTK 3D
viewers. However, note that due to the differencies between underlying API
of OCC and VTK libraries the behaviour of the functionality related to
the materials is different:
- presentation of the shape in OCC and VTK viewers is not fully identical;
- some material attributes can affect presentation in a different way.

\section material_opengl_model OpenGL ligthing model

The material is specifed by several attributes of the lighting
model. More details can be found in the documentation related to the
OpenGL programming, for example here: http://www.glprogramming.com/red/chapter05.html.

In the OpenGL lighting model, the light in a scene comes from several
light sources; the light sources have an effect only when there are
surfaces that absorb and reflect light. Each surface is assumed to be
composed of a material with various properties. A material might emit
its own light (like headlights on an automobile), it might scatter
some incoming light in all directions, and it might reflect a
portion of the incoming light in a preferential direction like a
mirror or other shiny surface.

The OpenGL lighting model considers the lighting to be divided into
four independent components: emissive, ambient, diffuse, and
specular. All four components are computed independently and then
added together. 

Ambient illumination is the light that has been scattered so much by the
environment that its direction is impossible to determine - it seems
to come from all directions. Backlighting in a room has a large
ambient component, since most of the light that reaches your eye has
first bounced off many surfaces. A spotlight outdoors has a tiny
ambient component; most of the light travels in the same direction,
and since you're outdoors, very little of the light reaches your eye
after bouncing off other objects. When ambient light strikes a
surface, it is scattered equally in all directions.

The diffuse component is the light that comes from one direction, so
it is brighter if it comes squarely down on a surface than if it barely
glances off the surface. Once it hits a surface, however, it's
scattered equally in all directions, so it appears equally bright, no
matter where the eye is located. Any light coming from a particular
position or direction probably has a diffuse component.

Finally, the specular light comes from a particular direction, and it
tends to bounce off the surface in a preferred direction. A
well-collimated laser beam bouncing off a high-quality mirror produces
specular reflection by almost 100 percent. Shiny metal or plastic has a
high specular component, and chalk or carpet has almost none. You can
think of specularity as shininess.

Although a light source delivers a single distribution of frequencies,
the ambient, diffuse, and specular components might be different. For
example, if you have a white light in a room with red walls, the
scattered light tends to be red, although the light directly striking
objects is white. OpenGL allows you to set the red, green, and blue
values for each component of light independently.  

\section material Material properties dialog box

The dialog box consists of two parts:
- The list box at the left shows all available material models, both
predefined by the application and custom one specified by the user.
- The widgets in the right part of the dialog box allows modifyng of
different properties of the material model.

The following properties of the material model can be specified:
- \b Ambient color and coefficient (floating point value between 0 and 1)
- \b Diffuse color and coefficient (floating point value between 0 and 1)
- \b Specular color and coefficient (floating point value between 0 and 1)
- \b Emissive color and coefficient (floating point value between 0
and 1). Note: this attribute is applicable only for the OCC viewer;
it simulates light originating from an object.
- \b Shininess
- \b Type of material model: \em physical or \em artificial.

If the material model is specified as a \em physical one (like \em Gold,
for instance), this means that the color of the shape (more precisely
its \em ambient color) can not be modified. If you assign a physical
material model to the shape, the "Color" menu item will not be
available in the popup menu.

If the model is non-physical (\em artificial), the color can be changed
to any appopriate one, only other attributes will be constant. In the
dialog box you will be able to modify the color of the shape via the
"Color" button. "Ambient color" button becomes disabled to signalize
that this attribute of the model is ignored. Also, it will be possible
to modify the color of the shape via the
\ref color_page "corresponding popup menu command".

All available predefined material models are shown in the list box of
the <b>Color and Material Properties</b> dialog:
- <b>[Current]</b> item in the list corresponds to the material model
  currently assigned to the selected shape(s). This model can be
  freely modified by the user.
- <b>Global</b> material models are shown in blue color in the list;
  these are the models predefined by the SALOME Geometry module. The user
  is not allowed to modify the global models.
- <b>User</b> materials are shown in black color in the list. These
  models are specified by the user and can be modified at any moment.

The buttons "Add material" and "Remove material" in the lower part of
the dialog box can be used to create or remove custom material
models. The same commands are also available via the popup menu that
is shown if the user presses right mouse button in the materials list
box. An additional "Rename material" command, available in popup menu,
can be used to change the name of material model.

<b>Examples:</b>

\image html material_OCC.png
<em>Different materials in OCC viewer</em>

\image html material_VTK.png
<em>Different materials in VTK viewer</em>

The default material model is specified via the preferences of Geometry
module.

*/