Category:LSL Light

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Properties of light

The quality of a PRIM_POINT_LIGHT cast by an object is determined by five parameters found on the features tab of the edit tool, which can also be set by script commands. The controls appear in the dialog in the same order as used in the script commands (see example below).

The first is a simple on/off switch: either the object is a PRIM_POINT_LIGHT source (checkbox activated or TRUE) or it isn't. The light's color is set by a color picker (dialog) or as an RGB vector (script) as usual. The intensity of light is a measurement of how strong in absolute terms the light is. This is a floating-point number ranging from 0.0 to 1.0, where 1.0 is fully on and 0.0 is equivalent to "off."

The two remaining settings are trickier, because their effects are quite subtle and they do interact with each other. Radius is the distance that light will travel from the centre of the object before it blends into and becomes indistinguishable from the scene's natural ambient lighting. This is a floating-point number measured in metres. Falloff is the extent to which light "decays" as it travels away from the object. This is a floating-point number ranging from 0.01 to 2.0, where 2.0 is an abrupt falling-off of intensity and 0.01 is relatively little change over distance.

To illustrate how these settings work, imagine—or better still: build—a hollow grey cube 8 by 8 by 8 metres on the inside, with a light source hovering in the middle of one end-wall, and yourself standing below the light source looking at the opposite wall. (Hint: if you do actually build this, turn the sun off while you are testing; you may also need to close the curtains and extinguish all lights in the real-life room you're working in.)

While the radius is less than 4 metres (i.e. under halfway to the opposite wall), it remains fairly dark. Turning the falloff up to 2.0 (maximum decay) makes the room somewhat darker.

As the radius approaches 8 metres (the distance to the wall), the room is only slightly brighter; at maximum falloff, the room is about as dark as it was when the radius was 4 metres and falloff was 0.01.

Only after the radius is greater than the distance to the opposite wall does it become significantly brighter. The effect of falloff is greater: when it is 0.01, direct illumination begins to make concentric circles on the wall, centred on the point where it intersects the light's axis; at the maximum of 2.0 the room is again as dark as it was when the radius was only 4 metres.

Controlling light sources

Light in Second Life is determined by the OpenGL standard which allows for eight sources. Traditionally and practically, two sources are reserved for the Sun and Moon, leaving six for incidental lighting. All eight are really generated on the client-side video card, so different video card models may show the same scene slightly differently. If more than six PRIM_POINT_LIGHT sources are present in a scene, only the light from the closest six will show in the environment.

An example - How to generate, switch and change light from LSL:

integer isLightTurnedOn;
 
default
{
    touch_start(integer total_number)
    {
//      toggle isLightTurnedOn between TRUE and FALSE
        isLightTurnedOn = !isLightTurnedOn;
 
        if (isLightTurnedOn)
        {
            llSetPrimitiveParams([
                PRIM_FULLBRIGHT, ALL_SIDES, FALSE,
                PRIM_POINT_LIGHT, FALSE, ZERO_VECTOR, 1.0, 10.0, 0.6]);
        }
        else
        {
            vector COLOR_ORANGE  = <1.000, 0.522, 0.106>;
 
            llSetPrimitiveParams([
                PRIM_FULLBRIGHT, ALL_SIDES, TRUE,
                PRIM_POINT_LIGHT, TRUE, COLOR_ORANGE, 1.0, 10.0, 0.6]);
        }
    }
}

The following example shows how to create a configurable light that turns itself on and off when touched. The light's properties can be edited by changing the values defined at the top of the script. This script illustrates the lighting attributes PRIM_POINT_LIGHT, PRIM_FULLBRIGHT and PRIM_GLOW.

// Touch the object to light it up.
// Lighting is configurable.
 
integer light_s    = TRUE;
vector  lightcolor = <1.0, 0.75, 0.5>;
float   intensity  = 1.0;             // 0.0 <= intensity <= 1.0
float   radius     = 10.0;            // 0.1 <= radius <= 20.0
float   falloff    = 0.01;            // 0.01 <= falloff <= 2.0
float   glow       = 0.05;
 
toggle()
{
    float thisglow = 0.0;
    light_s = !light_s;
 
    if (light_s)
        thisglow = glow;
 
    llSetPrimitiveParams([
        PRIM_POINT_LIGHT, light_s, lightcolor, intensity, radius, falloff,
        PRIM_FULLBRIGHT, ALL_SIDES, light_s,
        PRIM_GLOW,       ALL_SIDES, thisglow
    ]);
      llSetColor(lightcolor, ALL_SIDES);
}
 
default
{
    state_entry()
    {
        llSetText("Touch for light", <1.0, 1.0, 1.0>, 1.0);
        toggle();
    }
 
    touch_start(integer total_number)
    {
        toggle();
    }
}