vpShadeTable(3) Library Functions Manual vpShadeTable(3) NAME vpShadeTable - compute the contents of the shading lookup table SYNOPSIS #include <volpack.h> vpResult vpShadeTable(vpc) vpContext *vpc; ARGUMENTS vpc VolPack context from vpCreateContext. DESCRIPTION vpShadeTable computes the contents of the shading lookup table previously specified with vpLookupShader. For each entry in the table, the Phong shading equation is evaluated using the current lighting properties (as specified with vpSetLight), material properties (as specified with vpSetMa- terial), and viewing parameters (as specified with the view transformation commands). See vpSetMaterial(3) for a description of the shading calcula- tion. This function should be called before rendering a volume if any of the lighting or material properties have changed or if the viewpoint has changed since the last call to vpShadeTable. It should not be called if shading is performed using a callback function or if the shading lookup ta- bles are initialized by a user-defined routine. There is one state variable that affects the operation of vpShadeTable. If VP_CLAMP_SHADE_TABLE is enabled (see vpEnable(3)), then values are clamped to the range 0.0-255.0 before they are stored in the table. If this option is not enabled then no clamping is performed. Clamping is enabled by de- fault, but can be turned off to achieve special effects. For example, if all of the voxels in a data set have very low opacity then the rendered im- age may be very dark. To brighten it, multiply all of the material parame- ter coefficients by a constant, possibly making the values exceed 1.0, and turn off clamping. ERRORS The normal return value is VP_OK. The following error return values are possible: VPERROR_SINGULAR One of the current view transformation matrices is singular. VPERROR_BAD_SHADER The shading lookup tables are sized incorrectly, or one of the voxel fields used to index the tables is invalid, or the number of mater- ial types is invalid. VPERROR_BAD_SHADOW The angle between the shadow light vector and the viewing direction is too large (must be less than 45 degrees). Either change the light direction or disable shadows (see vpSetShadowLookupShader). SEE ALSO VolPack(3), vpCreateContext(3), vpCurrentMatrix(3), vpSetLookupShader(3), vpSetLight(3), vpSetMaterial(3) VolPack vpShadeTable(3)
NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | ERRORS | SEE ALSO
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