1vpSetLight(3) Library Functions Manual vpSetLight(3)
2
6 vpSetLight - set lighting properties
7
9 #include <volpack.h>
10 vpResult
12 vpSetLight(vpc, light_num, property, n0, n1, n2)
13 vpContext *vpc;
14 int light_num;
15 int property;
16 double n0, n1, n2;
17
19 vpc VolPack context from vpCreateContext.
20 light_num
22 A constant specifying a particular light source (VP_LIGHT0,
23 VP_LIGHT1, ..., VP_LIGHT5).
24 property
26 A constant specifying one lighting property (VP_COLOR or
27 VP_DIRECTION).
28 n0, n1, n2
30 Components of an RGB color (for VP_COLOR) or a direction vector
31 (for VP_DIRECTION).
32
34 vpSetLight is used to set the properties of a light source. VolPack
35 currently only supports directional light sources: each light is infin‐
36 itely distant, so it can be fully characterized by a direction vector
37 and a color. The lighting properties are used by vpShadeTable to com‐
38 pute the shading lookup table, which is then used to compute a color
39 for each voxel.
40 To initialize the lighting environment, call vpSetLight twice for each
42 light source which will be enabled. One call should set the RGB compo‐
43 nents of the light color (by using the VP_COLOR code for the property
44 parameter), and one call should set the XYZ components of the light
45 direction vector (by using the VP_DIRECTION code for the property
46 parameter). The particular light source is specified with one of the
47 light source codes defined in volpack.h: VP_LIGHT0, VP_LIGHT1, ...,
48 VP_LIGHT5. In the current implementation, at most six light sources
49 may be specified.
50 The RGB components of a light color should be numbers in the range 0.0
52 (zero intensity) to 1.0 (full intensity). For grayscale renderings
53 only the first (red) component is used and the other components may be
54 set to any legal value. The default is white light (1.0, 1.0, 1.0).
55 The light direction vector points from the light source towards the lit
57 object. It is transformed by the current contents of the modeling
58 matrix (see vpCurrentMatrix). This allows the direction vector to be
59 specified in an arbitrary coordinate system, provided the current mod‐
60 eling matrix properly transforms the vector into world coordinates.
61 The default is the vector (1,1,1).
62 Each light source contributes to the shading computation only if it is
64 enabled by calling vpEnable. By default, VP_LIGHT0 is enabled and all
65 other lights are disabled. The more light sources that are enabled,
66 the longer it takes to precompute the contents of the shading lookup
67 table.
68 One additional property of the light sources can be set with vpEnable:
70 VP_LIGHT_BOTH_SIDES. With this option enabled each light source shines
71 in two opposing directions, as if there were two light sources facing
72 each other with opposite direction vectors. No additional computation
73 is required when this option is enabled.
74
76 Information about the current lighting properties can be retrieved with
77 the following state variable codes (see vpGeti(3)):
78 VP_LIGHT_BOTH_SIDES.
79
81 The normal return value is VP_OK. The following error return values
82 are possible:
83 VPERROR_LIMIT_EXCEEDED
85 The light number is invalid or exceeds an implementation limit.
86 VPERROR_SINGULAR
88 The light direction vector is a zero vector.
89 VPERROR_BAD_VALUE
91 The RGB color components are out of range.
92 VPERROR_BAD_OPTION
94 The property argument is invalid.
95
97 VolPack(3), vpCreateContext(3), vpSetLookupShader(3), vpShadeTable(3),
98 vpGetLight(3)
99VolPack vpSetLight(3)