Environment Mapping + Source Lights - opengl

Question

I found a good example of environment mapping equirectangular. Here's the code:
VERTEX SHADER
varying vec3 Normal;
varying vec3 EyeDir;
varying float LightIntensity;
uniform vec3 LightPos;
void main(void){
gl_Position = ftransform();
Normal = normalize(gl_NormalMatrix * gl_Normal);
vec4 pos = gl_ModelViewMatrix * gl_Vertex;
EyeDir = pos.xyz;
LightIntensity = max(dot(normalize(LightPos - EyeDir), Normal), 0.0);
}
FRAGMENT SHADER
const vec3 Xunitvec = vec3 (1.0, 0.0, 0.0);
const vec3 Yunitvec = vec3 (0.0, 1.0, 0.0);
uniform vec3 BaseColor;
uniform float MixRatio;
uniform sampler2D EnvMap;
varying vec3 Normal;
varying vec3 EyeDir;
varying float LightIntensity;
void main (void){
// Compute reflection vector
vec3 reflectDir = reflect(EyeDir, Normal);
// Compute altitude and azimuth angles
vec2 index;
index.y = dot(normalize(reflectDir), Yunitvec);
reflectDir.y = 0.0;
index.x = dot(normalize(reflectDir), Xunitvec) * 0.5;
// Translate index values into proper range
if (reflectDir.z >= 0.0)
index = (index + 1.0) * 0.5;
else
{
index.t = (index.t + 1.0) * 0.5;
index.s = (-index.s) * 0.5 + 1.0;
}
// if reflectDir.z >= 0.0, s will go from 0.25 to 0.75
// if reflectDir.z < 0.0, s will go from 0.75 to 1.25, and
// that's OK, because we've set the texture to wrap.
// Do a lookup into the environment map.
vec3 envColor = vec3 (texture2D(EnvMap, index));
// Add lighting to base color and mix
vec3 base = LightIntensity * BaseColor;
envColor = mix(envColor, base, MixRatio);
gl_FragColor = vec4 (envColor, 1.0);
}
My problem is in the vertex shader.
LightIntensity = max(dot(normalize(LightPos - EyeDir), Normal), 0.0);
I'm subtracting the eye direction to the direction of light. But if I have more than one light source ... What I should do the calculation?
I use version 1.2 of GLSL.

Answer 1

Light is additive, so you just need to sum up the contributions of each light. If you have a fixed number of them, you can do that in a single pass through the shader—you just define a uniform for each light (position to start with, though you’ll probably want intensity/color as well) and calculate the final intensity like this:
LightIntensity = max(dot(normalize(Light1Pos - EyeDir), Normal), 0.0) + max(dot(normalize(Light2Pos - EyeDir), Normal), 0.0) + max(dot(normalize(Light3Pos - EyeDir), Normal), 0.0);