Advanced Programming with OpenGL ES 3.0 - Praise for OpenGL ES 30 Programming Guide - page 366

Lighting Shaders

Once we have tangent space normal maps and tangent space vectors set
up, we can proceed with per-fragment lighting. First, let's look at the
vertex shader in Example 14-1.

Example 14-1 Per-Fragment Lighting Vertex Shader

#version 300 es
uniform mat4 u_matViewInverse;
uniform mat4 u_matViewProjection;
uniform vec3 u_lightPosition;
uniform vec3 u_eyePosition;

in vec4 a_vertex;
in vec2 a_texcoord0;
in vec3 a_normal;
in vec3 a_binormal;
in vec3 a_tangent;

out vec2 v_texcoord;
out vec3 v_viewDirection;
out vec3 v_lightDirection;

void main( void )
{
// Transform eye vector into world space
vec3 eyePositionWorld =
(u_matViewInverse * vec4(u_eyePosition, 1.0)).xyz;

// Compute world−space direction vector
vec3 viewDirectionWorld = eyePositionWorld − a_vertex.xyz;

// Transform light position into world space
vec3 lightPositionWorld =
(u_matViewInverse * vec4(u_lightPosition, 1.0)).xyz;

// Compute world−space light direction vector
vec3 lightDirectionWorld = lightPositionWorld − a_vertex.xyz;

// Create the tangent matrix
mat3 tangentMat = mat3( a_tangent,
a_binormal,
a_normal );

// Transform the view and light vectors into tangent space
v_viewDirection = viewDirectionWorld * tangentMat;
v_lightDirection = lightDirectionWorld * tangentMat;

// Transform output position
gl_Position = u_matViewProjection * a_vertex;