HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 251

Chapter 10 L glLight Description glLight sets the values of individual light source parameters. light names the light and is a symbolic name of the form GL_LIGHTi, where 0 ≥ i < GL_MAX_LIGHTS. pname specifies one of ten light source parameters, again by symbolic name. params is either a single value or a pointer to an array that contains the new values. To enable and disable lighting calculation, call glEnable and glDisable with argument GL_LIGHTING. Lighting is initially disabled. When it is enabled, light sources that are enabled contribute to the lighting calculation. Light source i is enabled and disabled using glEnable and glDisable with argument GL_LIGHTi. The ten light parameters are as follows: GL_AMBIENT params contains four integer or floating-point values that specify the ambient RGBA intensity of the light. Integer values are mapped linearly such that the most positive representable value maps to 1.0, and the most negative representable value maps to 1.0. Floating-point values are mapped directly. Neither integer nor floating-point values are clamped. The initial ambient light intensity is (0, 0, 0, 1). GL_DIFFUSE params contains four integer or floating-point values that specify the diffuse RGBA intensity of the light. Integer values are mapped linearly such that the most positive representable value maps to 1.0, and the most negative representable value maps to 1.0. Floating-point values are mapped directly. Neither integer nor floating-point values are clamped. The initial value for GL_LIGHT0 is (1, 1, 1, 1); for other lights, the initial value is (0, 0, 0, 0). GL_SPECULAR params contains four integer or floating-point values that specify the specular RGBA intensity of the light. Integer values are mapped linearly such that the most positive representable value maps to 1.0, and the most negative representable value maps to 1.0. Floating-point values are mapped directly. Neither integer nor floating-point values are clamped. The initial value for GL_LIGHT0 is (1, 1, 1, 1); for other lights, the initial value is (0, 0, 0, 0). GL_POSITION params contains four integer or floating-point values that specify the position of the light in homogeneous object coordinates. Both integer and floating-point values are mapped directly. Neither integer nor floating-point values are clamped. The position is transformed by the modelview matrix when glLight is called (just as if it were a point), and it is stored in eye coordinates. If the w component of the position is 0, the light is treated as a directional source. Diffuse and specular lighting calculations take the light's direction, but not its actual position, into account, and attenuation is disabled. Otherwise, diffuse and specular lighting calculations are based on the actual location of the light in eye coordinates, and attenuation is enabled. The initial position is (0, 0, 1, 0); thus, the initial light source is directional, parallel to, and in the direction of the Z axis. GL_SPOT_DIRECTION params contains three integer or floating-point values that specify the direction of the light in homogeneous object coordinates. Both integer and floating-point values are mapped directly. Neither integer nor floating-point values are clamped. The spot 251