Create normalmap from image. Apply specular and lighting based on the generated normalmap.
See example for details on how to manage Light x,y. Specular x,y. Increasing light power creates more of a spotlight, higher specular power decreases specular.
Ported and adapted from:
shadertoy.com/view/4ss3W7
// by Nikos Papadopoulos, 4rknova / 2013
// Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.