gl.LightModel(pname, param)
gl.LightModel()
sets the lighting model parameter. pname
names a parameter and params gives the new value. There are three
lighting model parameters:
#GL_LIGHT_MODEL_AMBIENT
param
must contain four floating-point values that specify the ambient RGBA intensity of the entire scene. The initial ambient scene intensity is (0.2, 0.2, 0.2, 1.0).
#GL_LIGHT_MODEL_LOCAL_VIEWER
param
must be a single floating-point value that specifies how specular reflection angles are computed. If param
is 0, specular reflection angles take the
view direction to be parallel to and in the direction of the -z axis, regardless of the location of the vertex in eye coordinates. Otherwise, specular
reflections are computed from the origin of the eye coordinate system. The initial value is 0.
#GL_LIGHT_MODEL_TWO_SIDE
param
must be a single floating-point value that specifies whether one- or two-sided lighting calculations are done for polygons. It has no effect on
the lighting calculations for points, lines, or bitmaps. If param
is 0, one-sided lighting is specified, and only the front material parameters are
used in the lighting equation. Otherwise, two-sided lighting is specified. In this case, vertices of back-facing polygons are lighted using the back
material parameters and have their normals reversed before the lighting equation is evaluated. Vertices of front-facing polygons are always lighted
using the front material parameters, with no change to their normals. The initial value is 0.
In RGBA mode, the lighted color of a vertex is the sum of the material emission intensity, the product of the material ambient reflectance and the lighting model full-scene ambient intensity, and the contribution of each enabled light source. Each light source contributes the sum of three terms: ambient, diffuse, and specular. The ambient light source contribution is the product of the material ambient reflectance and the light's ambient intensity. The diffuse light source contribution is the product of the material diffuse reflectance, the light's diffuse intensity, and the dot product of the vertex's normal with the normalized vector from the vertex to the light source. The specular light source contribution is the product of the material specular reflectance, the light's specular intensity, and the dot product of the normalized vertex-to-eye and vertex-to-light vectors, raised to the power of the shininess of the material. All three light source contributions are attenuated equally based on the distance from the vertex to the light source and on light source direction, spread exponent, and spread cutoff angle. All dot products are replaced with 0 if they evaluate to a negative value.
The alpha component of the resulting lighted color is set to the alpha value of the material diffuse reflectance.
In color index mode, the value of the lighted index of a vertex ranges from the ambient to the specular values passed to gl.Material()
using #GL_COLOR_INDEXES
. Diffuse and specular coefficients, computed with a (.30, .59, .11) weighting of the lights' colors, the shininess of the material,
and the same reflection and attenuation equations as in the RGBA case, determine how much above ambient the resulting index is.
Please consult an OpenGL reference manual for more information.
pname
parameter, see above)#GL_INVALID_ENUM
is generated if pname
is not an accepted value.
#GL_INVALID_OPERATION
is generated if gl.LightModel()
is executed between the execution of gl.Begin() and the corresponding execution of gl.End().
#GL_LIGHT_MODEL_AMBIENT
gl.Get() with argument #GL_LIGHT_MODEL_LOCAL_VIEWER
gl.Get() with argument #GL_LIGHT_MODEL_TWO_SIDE
gl.IsEnabled() with argument #GL_LIGHTING