14. Diffuse lighting in fragment shader

Vertex shader

#version 130

in vec4 s_vPosition;
in vec4 s_vNormal;

uniform mat4 mM;    // model matrix
uniform mat4 mV;    // camera view matrix
uniform mat4 mP;    // perspective matrix

uniform mat4 mRotations; // all model rotations matrix

uniform vec4 vLight; // direction of light

out vec3 fN; // output of the normal
out vec3 fL; // output of light vector

void main () {
    
    // Rotate the normal and pass on as vec3
    fN = (mRotations*s_vNormal).xyz;
    fL = vLight.xyz;
    
    // From local, to world, to camera, to NDCs
    gl_Position = mP*mV*mM*s_vPosition;
}

Fragment shader

#version 130

in vec3 fN;
in vec3 fL;

out vec4 fColor;

void main () {
    // NOTE: We ALWAYS need to normalize the vectors after interpolation!
    vec3 N = normalize(fN);
    vec3 L = normalize(fL);
    float diffuse_intensity = max(dot(N, L), 0.0);
    vec4 light_color = vec4( 1.0, 1.0, 0.0, 1.0); // R + G = yellow
    fColor = light_color * diffuse_intensity; // yellow diffuse light
}