GXInitLightSpot

Syntax

#include <revolution/gx.h>

void GXInitLightSpot(
    GXLightObj* lt_obj,
    f32         cutoff,
    GXSpotFn    spot_func );

Arguments

Return Values

None.

Description

This function sets coefficients for angular (spotlight) attenuation in light objects. This can be also set with the GXInitLightAttn function. This function uses two easy-to-control parameters instead of a0, a1, and a2, which are used by the GXInitLightAttn function.

The cutoff argument specifies the spotlight's cutoff angle in degrees. The spotlight works when the angle between the ray for a vertex and the light direction given by the GXInitLightDir function is smaller than this cutoff angle. The value used for cutoff should be 0 < cutoff <= 90.0. Otherwise, the given light object doesn't become a spotlight. (Some spotlight types require tighter range.) 

The spot_func argument defines the type of the illumination distribution to be used within the cutoff angle. The following graphs show the curves of the distribution functions given by acceptable values for spot_func. The value GX_SP_OFF turns the spotlight feature off even if the color channel setting uses GX_AF_SPOT (see the GXSetChanCtrl function).

Graph
Type	GX_SP_FLAT	GX_SP_COS	GX_SP_COS2
Valid Range	0 < cutoff <= 90	0 < cutoff <= 90	0 < cutoff <= 90
Graph
Type	GX_SP_SHARP	GX_SP_RING1	GX_SP_RING2
Valid Range	30 < cutoff <= 90	30 < cutoff <= 90	30 < cutoff <= 90

This function can generate only some kinds of simple spotlights. For more flexible control, use the GXInitLightAttn function and calculate the appropriate coefficients.

This function sets parameters only for angular attenuation. Parameters for distance attenuation may be set using the GXInitLightDistAttn or GXInitLightAttnK function.

This function does not load any hardware registers directly. To load a light object into a hardware light, use the GXLoadLightObjImm or GXLoadLightObjIndx function.

See Also

GXInitLightAttn, GXInitLightAttnA, GXInitLightAttnK, GXInitLightDistAttn, GXLightObj Initialization Flow

Revision History

2006/03/01 Initial version.

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