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#include <OSGConfig.h> |
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using namespace OSG; |
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/*! \defgroup GrpSystemMaterial Materials |
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\ingroup GrpSystem |
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Materials define the surface properties of the geometry and abstract the actual |
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implementation from the user. |
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See \ref PageSystemMaterial for a detailed description. |
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*/ |
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/*! \page PageSystemMaterial Materials |
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\latexonly Starter:NewChapter \endlatexonly |
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Materials define the surface properties of the geometry. For the standard |
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Phong lighting model that OpenGL uses these are ambient, diffuse and specular |
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color as well as shininess. However, this is an area where extensions are |
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added at an amazing pace. The purpose of materials is to add a level of |
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abstraction and give the user an easy to use interface to define surface |
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properties without having to worry about the details of realizing them (e.g. |
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how to use multiple passes, when and how to calculate derived information like |
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tangents and binormals etc.). |
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This area is quickly expanding, so what we have right now is just the |
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beginning. |
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\ext To use a Material the geometry will call the Material's |
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osg::Material::draw() method, which decides what to do. Right now all it can |
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do is directly draw itself or pass itself to the Rendering Backend to be |
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rendered later. To actually be used by the renderer Materials have a method to |
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give out a osg::State to be used to render their associated geometry. For |
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efficiency reasons this State should be kept ready to use in the Material and |
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returned when needed. |
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This whole interface is a bit convoluted, unclear, can't handle all the cases |
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that it should and thus will change pretty soon. Stay tuned.\endext |
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\section PageSystemMaterialTypes Material types |
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\subsection PageSystemMaterialChunkMaterial ChunkMaterial |
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The osg::ChunkMaterial is a material that is just a collection of \ref |
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StateChunk "osg::StateChunks". This allows adding and using new |
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extensions in the form of state chunks pretty easily. |
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It is also the base class for the simple materials given below. |
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\subsection PageSystemMaterialSimpleMaterial SimpleMaterial |
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The osg::SimpleMaterial is a pretty direct mapping of the OpenGL light model. |
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It has colors for ambient, diffuse, specular and emission properties, and a |
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shininess value. In addition to that it has a transparency setting, ranging |
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from 0 for opaque to 1 for fully transparent. |
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There are two other attributes in a SimpleMaterial that control the appearance |
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of an object. One is the lit attribute, which defines if the material is |
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influenced by light sources at all. If it isn't, the color is directly taken |
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from the diffuseColor component and other color attributes are ignored. |
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The other attribute is the colorMaterial field, which defines how colors that |
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are given in the geometry influence the lighting calculation. By default they |
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replace the diffuse color only. Possible values are taken from the |
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glColorMaterial() call, the most useful being GL_DIFFUSE_AND_SPECULAR. One |
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possible value that is not used by glColorMaterial() is GL_NONE, which |
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switches off the color material handling and thus ignores colors that are |
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given in the geometry. |
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As SimpleMaterial is derived from osg::ChunkMaterial, other attributes can be |
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added in the form of \ref StateChunk "StateChunks". |
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\subsection PageSystemMaterialTexturedSimpleMaterial TexturedSimpleMaterial |
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osg::SimpleTexturedMaterial is derived from osg::SimpleMaterial and adds a |
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texture. The texture is defined by an image (see \ref PageSystemImage for details on |
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how to define or load an image). |
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Additionally there are some parameters to define the behavior of a texture. |
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magFilter and minFilter define how to scale the texture image up or down, |
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legal values taken from glTexParameter(). The most useful ones are GL_NEAREST |
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or GL_LINEAR for magFilter, and additionally GL_LINEAR_MIPMAP_LINEAR for |
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minFilter. |
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envMode defines how a color from the texture is combined with a color from the |
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lighting calculation. The default is GL_REPLACE which completely ignores the |
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lighting color. Other useful values are GL_MODULATE, which just multiplies the |
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two, and GL_DECAL, which interpolates between lighting and texture based on |
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the texture's alpha channel. |
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Finally, a texture can be used as a spherical environment map to simulate a |
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reflective object by setting the envMap field to true. Spherical environment |
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maps need to display the image of a reflective sphere in the middle of the |
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environment that is being reflected. |
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As TexturedSimpleMaterial is derived from osg::ChunkMaterial, other attributes |
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can be added in the form of \ref StateChunk "StateChunks". |
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*/ |
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