Matrix definition issues

[Valentin_Bonneau]

Hello all.

To follow up on ToonTank course, I’m trying to solidify my knowledge by working on a personnal project.
I want to program 6-axis industrial robot movements.
To do that, I need to do a lot of change of base calculations (global to local space) and consider not only translation but also rotations.
Matrices should be an easy way to do this, but I’m having trouble to define them.
I’ve tried the following :

• in .h file :

      FRotationTranslationMatrix T_Base(FRotator(), FVector()); 
  

• in .cpp file :

    const FRotator& TempRot = BaseMesh->GetRelativeRotation();
  
    const FVector& TempPos = BaseMesh->GetRelativeLocation();
  
    T_Base(TempRot, TempPos);
  

I get the following error message on T_Base :

il n'existe aucune fonction de conversion appropriée de "const FRotator" en "FRotator (*)()"
il n'existe aucune fonction de conversion appropriée de "const FVector" en "FVector (*)()"

which should translate by something like :

There is no proper conversion function from "const FRotator" to "FRotator (*)()"

Any idea why this not working?

[DanM]

There’s two issues with this.

1. You have stumbled upon “the most vexing parse”.

   FRotationTranslationMatrix T_Base(FRotator(), FVector()); 
   

   This is actually a function declaration. This declares a function called T_Base that returns FRotationTranslationMatrix and takes two function pointers that have no parameters and return FRotator and FVector respecitively e.g.

   FRotator Foo();
   FVector Bar();
   
   T_Base(Foo, Bar); // call T_Base passing the address of Foo and Bar
   

   This can be resolved using braces instead

   // Any of these replacements of () to {} should work
   FRotationTranslationMatrix T_Base{FRotator(), FVector()}; // just the outer
   FRotationTranslationMatrix T_Base{FRotator{}, FVector{}); // just the inner
   FRotationTranslationMatrix T_Base{FRotator{}, FVector{}}; // all
   

2. If T_Base were fixed to be a variable of type FRotationTranslationMatrix

   T_Base(TempRot, TempPos);
   

   This would be using the function call operator

   FRotationTranslationMatrix::operator()(const FVector&, const FRotator&);   
   

   as the variable has already been defined and initialised. You would need to use the assignment operator = to assign a new value.

   T_Base = FRotationTranslationMatrix(TempRot, TempPos);
   

[Valentin_Bonneau]

Thanks a lot for the information!
I’ll try this