Parallax Corrected Cubemaps in Opengl? - c++

Question

I have been trying to imploment parallax corrected local cubemaps in OpenGL for a little while now, but I've not really managed to get anywhere, does anybody know where to start?
Here is my current shader code:
Fragment:
#version 330
in vec2 TexCoord;
in vec3 Normal;
in vec3 Position;
in vec3 Color;
out vec4 color;
uniform samplerCube CubeMap;
uniform vec3 CameraPosition;
void main() {
vec4 OutColor = vec4(Color,1.0);
vec3 normal = normalize(Normal);
vec3 view = normalize(Position-CameraPosition);
vec3 ReflectionVector = reflect(view,normal);
vec4 ReflectionColor = texture(CubeMap,ReflectionVector);
OutColor = mix(OutColor,ReflectionColor,0.5);
color = OutColor;
}
Vertex:
#version 330
layout (location = 0) in vec3 position;
layout (location = 2) in vec3 normal;
layout (location = 1) in vec2 texCoord;
layout (location = 3) in vec3 color;
out vec2 TexCoord;
out vec3 Normal;
out vec3 Position;
out vec3 Color;
uniform mat4 ModelMatrix;
uniform mat4 ViewMatrix;
uniform mat4 ProjectionMatrix;
void main()
{
gl_Position = ProjectionMatrix * ViewMatrix * ModelMatrix * vec4(position, 1.0f);
TexCoord=texCoord;
Normal = normal;
Position = vec4(ModelMatrix * vec4(position,1.0)).xyz;
Color = color;
}

Answer 1

Position = vec4(ModelMatrix * vec4(position,1.0)).xyz;
This puts the Position output variable into world space. Assuming the CameraPosition uniform is also in world space, then:
vec3 view = normalize(Position-CameraPosition);
view will also be in world space.
However, Normal comes directly from the vertex attribute. So unless you are updating each vertex's Normal value every time you rotate the object, that value will probably be in model space. And therefore:
vec3 ReflectionVector = reflect(view,normal);
This statement is incoherent. view is in one space, while normal is in another. And you can't really perform reasonable operations on vectors that are in different coordinate systems.
You need to make sure that Normal, Position, and CameraPosition are all in the same space. If you want that space to be world space, then you need to transform Normal into world space. Which in the general case requires computing the inverse/transpose of your model-to-world matrix.