float u = fragCoord.x / iResolution.x * 2.0 - 1.0;
float v = fragCoord.y / iResolution.y * 2.0 - 1.0;

vec3 eye = vec3();
vec3 tar = vec3();

vec3 dir = normalize(tar - eye);
vec3 right = normalize(cross(vec3(0, 1, 0), dir));
vec3 up = cross(dir, right);

vec3 ro = eye;
vec3 rd = normalize(dir + right*u + up*v);