.vert

#version 150

uniform mat4 MVPMatrix;
uniform mat3 normalMatrix;

in vec3 position;
in vec3 normal;

out Data {
    vec3 normal;
} DataOut;

void main()
{
    DataOut.normal = normalize(normalMatrix * normal);

    gl_Position = MVPMatrix * vec4(position, 1.0);
}

.frag

#version 150

uniform vec3 diffuse = vec3(0.72265625, 0.4765625, 0.33984375);
uniform vec3 l_dir;

in Data {
    vec3 normal;
} DataIn;

out vec4 outputColor;

void main()
{

    vec3 n = normalize(DataIn.normal);

    float intensity = max(dot(n, l_dir), 0.0);

    outputColor = vec4(intensity * diffuse, 1.0);
}