Function specular_lighting 

pub fn specular_lighting(
    fe: &SpecularLighting,
    light_source: LightSource,
    src: ImageRef<'_>,
    dest: ImageRefMut<'_>,
)

Renders a specular lighting.

• src pixels can have any alpha method, since only the alpha channel is used.
• dest will have a premultiplied alpha.

Does nothing when src is less than 3x3.

Panics

• When src and dest have different sizes.