Environment Mapping + Source Lights

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);