llSetAlpha(float alpha, integer face)

Sets the opacity (also called alpha) of a face or all faces of the current prim.

A float value between 0.0 and 1.0 being the degree of opacity. 1.0 being fully opaque.

An integer value defining the face of the prim to be affected. ALL_SIDES affects all faces.

• This function ONLY affects the prim the script is in. To change the alpha on another prim, use llSetLinkAlpha.
• Note that the viewer shows transparency, not opacity, and it shows it in percentage. To convert from viewer transparency to an alpha value suitable for use with this function, use this formula: alpha=(100-transparency)/100. For example, a transparency of 35% is an alpha value of 0.65.

llSetAlpha(0.5, ALL_SIDES); // will set all faces of the current prim to semi-opaque

llSetAlpha-example.lsl

default
{
    state_entry()
    {
        llSetAlpha(0.0, 2);  // Will make face 2 of this prim go transparent
    }
}

• llSetLinkAlpha to change the opacity on any chosen prim in the current object.
• llSetColor to set the color of a face in the current prim, or llSetLinkColor to set it for any chosen prim.
• The PrimitiveParams family of functions, with PRIM_COLOR, allows changing color and alpha at the same time.
• llSetTexture and llSetLinkTexture can also be used to change the texture to TEXTURE_TRANSPARENT.