Porting Lighting and Materials Functions

OpenGL functions for lighting and materials differ substantially from the IRIS GL functions. Unlike IRIS GL, OpenGL has separate functions for setting lights, light models and materials.

Keep the following points in mind when porting lighting and materials functions:

OpenGL has no table of stored definitions. You can use display lists to mimic the IRIS GL def/bind mechanism. For more information on defs and binds, see Porting Defs, Binds, and Sets.
With OpenGL, attenuation is associated with each light source, rather than the overall lighting model.
Diffuse and specular components are separated in OpenGL light sources.
OpenGL light sources have an alpha component. When porting your IRIS GL code, set this alpha component to 1.0, indicating 100 percent opaque. The alpha values are then determined by the alpha component of your materials only, so the objects in your scene will look the same as they did in IRIS GL.

The following table lists IRIS GL lighting and materials functions and their equivalent OpenGL functions.

IRIS GL Function	OpenGL Function	Meaning
Imdef(DEFLIGHT, ...)	glLight	Define a light source.
Imdef(DEFLMODEL, ...)	glLightModel	Define a lighting model.
Imbind	glEnable(GL_LIGHTi)	Enable light i.
Imbind	glEnable(GL_LIGHTING)	Enable lighting.
Imdef(DEFMATERIAL, ...)	glMaterial	Define a material.
Imcolor	glColorMaterial	Change the effect of color commands while lighting is active.
—	glGetMaterial	Get material parameters.

The following table lists various IRIS GL material parameters and their equivalent OpenGL parameters.

Imdef Index	glMaterial Parameter	Default	Meaning
ALPHA	GL_DIFFUSE	—	The fourth value in the GL_DIFFUSE parameter specifies the alpha value.
AMBIENT	GL_AMBIENT	(0.2, 0.2, 0.2, 1.0)	Ambient color.
DIFFUSE	GL_DIFFUSE	(0.8, 0.8, 0.8, 1.0)	Diffuse color.
SPECULAR	GL_SPECULAR	(0.0, 0.0, 0.0, 1.0)	Emissive color.
SHININESS	GL_SHININESS GL_AMBIENT_ AND_DIFFUSE	0.0	Specular exponent. Equivalent to calling glMaterial twice with the same values.
COLORINDEXES	GL_COLOR_ INDEXES	—	Color indexes for ambient, diffuse, and specular lighting.

When the first parameter of Imdef is DEFMODEL, the equivalent OpenGL translation is the function glLightModel. The exception is when the parameter following DEFMODEL is ATTENUATION: then the equivalent OpenGL function is glLight.

The following table lists the equivalent lighting model parameters for IRIS GL and OpenGL.

Imdef Index	glLightModel Parameter	Default	Meaning
AMBIENT	GL_LIGHT_ MODEL_AMBIENT	(0.2, 0.2, 0.2, 1.0)	Ambient color of scene.
ATTENUATION	—	—	See glLight.
LOCALVIEWER	GL_LIGHT_MODEL_ LOCAL_VIEWER	GL_FALSE	Viewer local (TRUE) or infinite (FALSE).
TWOSIDE	GL_LIGHTMODEL_ TWO_SIDE	GL_FALSE	Use two-sided lighting when TRUE.

When the first parameter of Imdef is DEFLIGHT, the equivalent OpenGL translation is the glLight function.

The following table lists the equivalent lighting parameters for IRIS GL and OpenGL.

Imdef Index	glLight Parameter	Default	Meaning
AMBIENT	GL_AMBIENT GL_DIFFUSE GL_SPECULAR	(0.0, 0.0, 0.0, 1.0) (1.0, 1.0, 1.0, 1.0) (1.0, 1.0, 1.0, 1.0)	Ambient intensity. Diffuse intensity. Specular intensity.
LCOLOR	No equivalent.	—	—
POSITION	GL_POSITION	(0.0, 0.0, 1.0, 0.0)	Position of light.
SPOTDIRECTION	GL_SPOT_ DIRECTION	(0, 0, –1)	Direction of spotlight.
SPOTLIGHT	GL_SPOT_ EXPONENT GL_SPOT_CUTOFF	0 180	Intensity distribution. Maximum spread angle of light source.
DEFMODEL, ATTENUATION	GL_CONSTANT_ ATTENUATION GL_LINEAR_ ATTENUATION GL_QUADRATIC_ ATTENUATION	(1, 0, 0)	Attenuation factors.