Vertex Shaders - Praise for OpenGL ES 30 Programming Guide - page 204

Example 8-3 Spotlight (continued)

vec4 specular_color;
float specular_exponent;
};

const float c_zero = 0.0;
const float c_one = 1.0;

uniform material_properties material;
uniform spot_light light;

// normal and position are normal and position values in
// eye space.
// normal is a normalized vector.
// This function returns the computed color.

vec4 spot_light_color ( vec3 normal, vec4 position )
{
vec4 computed_color = vec4 ( c_zero, c_zero, c_zero,
c_zero );
vec3 lightdir;
vec3 halfplane;
float ndotl, ndoth;
float att_factor;

att_factor = c_one;

// we assume "w" values for light position and
// vertex position are the same
lightdir = light.position.xyz - position.xyz;

// compute distance attenuation
if ( light.compute_distance_attenuation )
{
vec3 att_dist;
att_dist.x = c_one;
att_dist.z = dot ( lightdir, lightdir );
att_dist.y = sqrt ( att_dist.z );
att_factor = c_one / dot ( att_dist,
light.attenuation_factors );
}

// normalize the light direction vector
lightdir = normalize ( lightdir );

// compute spot cutoff factor
if ( light.spot_cutoff_angle < 180.0 )
{
float spot_factor = dot ( -lightdir,
light.spot_direction );