calculate the perspective projection view frustum in opengl

ViewFrustum.cpp

void ViewFrustum::calculate( const float fov , const float aspectratio , const float n , const float f )
{
	float nearPlane = -n;
	float farPlane = -f;

	float y1 = nearPlane * tanf(torad(fov)/2.0f);
	float y2 = farPlane * tanf(torad(fov)/2.0f);

	// calculate the horizontal fov from the vertical one
	float fov_horizontal = 2.0f * atanf( tanf(torad(fov)/2.0f) * aspectratio );

	float x1 = nearPlane * tanf(fov_horizontal/2.0f);
	float x2 = farPlane * tanf(fov_horizontal/2.0f);

	// near vertices
	this->vertices[0] = vec3( x1 , -y1 , n );
	this->vertices[1] = vec3( x1 , y1 , n );
	this->vertices[2] = vec3( -x1 , y1 , n );
	this->vertices[3] = vec3( -x1 , -y1 , n );
	// far vertices
	this->vertices[4] = vec3( x2 , -y2 , f );
	this->vertices[5] = vec3( x2 , y2 , f );
	this->vertices[6] = vec3( -x2 , y2 , f );
	this->vertices[7] = vec3( -x2 , -y2 , f );
}

void ViewFrustum::convertToWorldSpace( const mat4& M_view_inv )
{
	for ( uint i = 0 ; i < 8 ; ++i )
	{
		vec4 v = M_view_inv * vec4( this->vertices[i] , 1.0f );
		this->vertices[i] = vec3( v.x , v.y , v.z );
	}
}