I've been stuck on this problem for two days. I've read many articles about transforming normals, but I'm just totaly stuck. I understand choping off W component for "turning off" translation, and doing inverse/traspose transformation for non-uniform scaling problem, but my bug seems to be from a different source.

So, I've imported a simple ball into OpenGL. Only transformation that I'm applying is rotation over time. But when my ball rotates, the illuminated part of the ball moves around just as it would if direction light direction was changing.

I just can't figure out what is the problem. Can anyone help me with this?

Here's the GLSL code:

Vertex Shader:

#version 440 core

uniform mat4 World, View, Projection;

layout(location = 0) in vec3 VertexPosition;

layout(location = 1) in vec3 VertexColor;

layout(location = 2) in vec3 VertexNormal;

out vec4 Color;
out vec3 Normal;

void main()
{
    Color = vec4(VertexColor, 1.0);

    vec4 n = World * vec4(VertexNormal, 0.0f);
    Normal = n.xyz;

    gl_Position = Projection * View * World * vec4(VertexPosition, 1.0);
}

Fragment Shader:

#version 440 core

uniform vec3 LightDirection = vec3(0.0, 0.0, -1.0);
uniform vec3 LightColor = vec3(1f);

in vec4 Color;
in vec3 Normal;

out vec4 FragColor;

void main()
{
    diffuse = max(0.0, dot(normalize(-LightDirection), normalize(Normal)));
    vec4 scatteredLight = vec4(LightColor * diffuse, 1.0f);

    FragColor = min(Color * scatteredLight, vec4(1.0));

}