const float feather = 0.5;

attribute vec3 pos;

attribute vec3 loc;

attribute vec3 tgt;

uniform mat4 modelview;

uniform mat4 projection;

uniform float width;

uniform float pixel;

varying vec3 fragLoc;

void main() {

// get camera direction from modelview matrix

vec3 dir = vec3(modelview[0].z, modelview[1].z, modelview[2].z);

// calculate line contour extension basis for constant width and caps

vec3 norm = normalize(cross(tgt, dir));

norm = normalize(norm - dir * dot(dir, norm));

vec3 perp = normalize(cross(dir, norm));

// calculate line extension width considering antialiasing

float ext = width + feather * pixel;

// extend line contour

vec3 vertex = pos;

vertex += ext * loc.x * normalize(perp);

vertex += ext * loc.y * normalize(norm);

// write fragment location for calculating caps and antialiasing

fragLoc = loc;

// transform resulting vertex with modelview and projection matrices

gl_Position = projection * modelview * vec4(vertex, 1.0);

}