openGL cubemap reflections in view space are wrong

Question

I am following this tutorial and I managed to add a cube map to my scene. Then I tried to add reflections to my object, differently from the tutorial, I made my GLSL code in view space. However, the reflections seem a bit off. They are always reflecting the same side whatever angle you are facing, in my case, you always see a rock on the reflected object, but the rock is only on one side of my cube map. Here is a video showing the effect:

.

I tried with other shaped objects, like a cube, and the effect is the same. I also found this book, that shows an example of a view space reflections, and it seems I am doing something similar to it, but it still won't result in the desired effect. My vertex shader code:

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 normal;
layout (location = 2) in vec2 aTexCoord;

uniform mat4 Model;
uniform mat4 View;
uniform mat4 Projection;

out vec2 TexCoord;
out vec3 aNormal;
out vec3 FragPos;

void main()
{
    aNormal = mat3(transpose(inverse(View * Model))) * normal; 
    FragPos = vec3(View * Model * vec4(aPos,1.0));
    gl_Position = Projection * vec4(FragPos,1.0);
    TexCoord = aTexCoord;
}

My vertex code:

#version 330 core

out vec4 FragColor;

in vec3 FragPos;
in vec3 aNormal;

uniform samplerCube skybox;


void main(){
    vec3 I = normalize(FragPos);
    vec3 R = reflect(I,normalize(aNormal));
    FragColor = vec4(texture(skybox,R).rgb,1.0);
}

Answer 1

Since you do the computations, in the fragment shader, in view space, the reflected vector (R) is a vector in view space, too. The cubemap (skybox) represents a map of the environment, in world space. You have to transform R form view space to world space. That can be done by the inverse view matrix The inverse matrix can be computed by the glsl built-in function inverse:

#version 330 core

out vec4 FragColor;

in vec3 FragPos;
in vec3 aNormal;

uniform samplerCube skybox;
uniform mat4 View;

void main() {
    vec3 I      = normalize(FragPos);
    vec3 viewR  = reflect(I, normalize(aNormal));
    vec3 worldR = inverse(mat3(View)) * viewR;
    FragColor   = vec4(texture(skybox, worldR).rgb, 1.0);
}

Note, the view matrix transforms form world space to view space, this the inverse view matrix transforms form view space to world space. See also Invertible matrix.