struct vec2
{
union
{
struct { float x, y; };
struct { float r, g; };
struct { float s, t; };
};
vec2() {}
vec2(float a, float b) : x(a), y(b) {}
};
struct vec3
{
union
{
struct { float x, y, z; };
struct { float r, g, b; };
struct { float s, t, p; };
// Here is the problem with g++.
struct { vec2 xy; float z; };
struct { float x; vec2 yz; };
};
vec3() {}
vec3(float a, float b, float c) : x(a), y(b), z(c) {}
};
The code above compiles and works as expected in Visual Studio and so I can use it like
vec3 v1(1.f, 2.f, 3.f);
vec2 v2 = v1.yz; // (2, 3)
Not in g++ (MinGW).
src/main.cpp:22:23: error: member 'vec2 vec3::<unnamed union>::<unnamed struct>::xy' with constructor not allowed in anonymous aggregate
src/main.cpp:22:33: error: redeclaration of 'float vec3::<unnamed union>::<unnamed struct>::z'
src/main.cpp:18:30: note: previous declaration 'float vec3::<unnamed union>::<unnamed struct>::z'
src/main.cpp:23:32: error: member 'vec2 vec3::<unnamed union>::<unnamed struct>::yz' with constructor not allowed in anonymous aggregate
src/main.cpp:23:24: error: redeclaration of 'float vec3::<unnamed union>::<unnamed struct>::x'
src/main.cpp:18:24: note: previous declaration 'float vec3::<unnamed union>::<unnamed struct>::x'
I think I shouldn't be doing it like that in the first place. Any Ideas?
Edit: After reading a lot of articles and exploring open-source projects, I started to get how vector swizzling should be like and posted the solution below, still waiting for better answers though.
Edit 2: All
vec*
members must be accessed only from the parent like the GLM library.
Well, I've found the solution myself using only the C++ Standards.
No command-lines neither using compiler-specific code.
So this is my new and simple implementation
template<unsigned int I>
struct scalar_swizzle
{
float v[1];
float &operator=(const float x)
{
v[I] = x;
return v[I];
}
operator float() const
{
return v[I];
}
float operator++(int)
{
return v[I]++;
}
float operator++()
{
return ++v[I];
}
float operator--(int)
{
return v[I]--;
}
float operator--()
{
return --v[I];
}
};
// We use a vec_type in a template instead of forward declartions to prevent erros in some compilers.
template<typename vec_type, unsigned int A, unsigned int B>
struct vec2_swizzle
{
float d[2];
vec_type operator=(const vec_type& vec)
{
return vec_type(d[A] = vec.x, d[B] = vec.y);
}
operator vec_type()
{
return vec_type(d[A], d[B]);
}
};
struct vec2
{
union
{
float d[2];
scalar_swizzle<0> x, r, s;
scalar_swizzle<1> y, g, t;
vec2_swizzle<vec2, 0, 0> xx;
vec2_swizzle<vec2, 1, 1> yy;
};
vec2() {}
vec2(float all)
{
x = y = all;
}
vec2(float a, float b)
{
x = a;
y = b;
}
};
/* Debugging */
inline std::ostream& operator<<(std::ostream &os, vec2 vec)
{
os << "(" << vec.x << ", " << vec.y << ")";
return os;
}
template<typename vec_type, unsigned int A, unsigned int B, unsigned int C>
struct vec3_swizzle
{
float d[3];
vec_type operator=(const vec_type& vec)
{
return vec_type(d[A] = vec.x, d[B] = vec.y, d[C] = vec.z);
}
operator vec_type()
{
return vec_type(d[A], d[B], d[C]);
}
};
struct vec3
{
union
{
float d[3];
scalar_swizzle<0> x, r, s;
scalar_swizzle<1> y, g, t;
scalar_swizzle<2> z, b, p;
vec2_swizzle<vec2, 0, 1> xy;
vec2_swizzle<vec2, 1, 2> yz;
vec3_swizzle<vec3, 0, 1, 2> xyz;
vec3_swizzle<vec3, 2, 1, 0> zyx;
};
vec3() {}
vec3(float all)
{
x = y = z = all;
}
vec3(float a, float b, float c)
{
x = a;
y = b;
z = c;
}
};
/* Debugging */
inline std::ostream& operator<<(std::ostream &os, vec3 vec)
{
os << "(" << vec.x << ", " << vec.y << ", " << vec.z << ")";
return os;
}
Of course, you can add/create more swizzlings. Now with a little test.
int main()
{
vec3 v0(10, 20, 30);
std::cout << v0.zyx << std::endl;
vec2 c(-5, -5);
v0.xy = c;
vec2 v1(v0.yz);
std::cout << v0 << std::endl;
std::cout << v1 << std::endl;
vec3 v(50, 60, 70);
vec2 d = v.yz;
std::cout << d << std::endl;
float f = d.x * d.y;
std::cout << f << std::endl;
return 0;
}
Out:
(30, 20, 10)
(-5, -5, 30)
(-5, 30)
(60, 70)
4200
You can print the vectors for debugging with std::cout
if you're not using an IDE as I did in gcc.
First, anonymous struct is a feature from C11, and is not allowed by C++, so it does not support class members with constructors (not a C struct). To write portable C++ code, you should avoid anonymous struct:
struct vec2 // use C++ style struct declaration
{
// struct is public by default
union
{
struct { float x, y; } xy; // add member name,
struct { float r, g; } rg; // now the declaration declares a member
struct { float s, t; } st; // instead of an anonymous struct
};
vec2() {}
vec2(float a, float b) : xy{a, b} {}
// ^^^^^^^^ also change the initialization
};
struct vec3
{
public:
union
{
struct { float x, y, z; } xyz; //
struct { float r, g, b; } rgb; //
struct { float s, t, p; } stp; // add member name
struct { vec2 xy; float z; } vecz; //
struct { float x; vec2 yz; } xvec; //
};
vec3() {}
vec3(float a, float b, float c) : xyz{a, b, c} {}
// ^^^^^^^^ also change the initialization
};
Now the code compiles under GCC, but that's not enough. Under Clang with -pedantic-errors
, you'll get several errors:
error: anonymous types declared in an anonymous union are an extension [-Werror,-Wnested-anon-types]
This is because you cannot declare a nested type in an anonymous union, so you should also move these struct definitions outside the union:
struct vec2
{
struct XY { float x, y; };
struct RG { float r, g; };
struct ST { float s, t; };
union
{
XY xy;
RG rg;
ST st;
};
vec2() {}
vec2(float a, float b) : xy{a, b} {}
};
struct vec3
{
struct XYZ { float x, y, z; };
struct RGB { float r, g, b; };
struct STP { float s, t, p; };
struct VECZ { vec2 xy; float z; };
struct XVEC { float x; vec2 yz; };
union
{
XYZ xyz;
RGB rgb;
STP stp;
VECZ vecz;
XVEC xvec;
};
vec3() {}
vec3(float a, float b, float c) : xyz{a, b, c} {}
};
Although this solution works, you can only access the members via, for example, v.xy.x
, instead of simple v.x
. In addition, aliasing vec2
with two float
s would result in undefined behavior. I think there is no standard solution to achieve vector swizzling perfectly.
For non-standard solution, one can use a proxy class without constructors instead of vec2
to make the compiler work. The GLM library also uses this idea. OP has already posted an answer as a complete implementation of this idea.
As for "member with constructor not allowed in anonymous aggregate", , is due to compiler running in compliance with older standard, because as of C++11, unions can have members with non-trivial constructors (you defined your own constructor, so it's non-trivial, details about this can be found here). Add -std=c++11 in your g++ compiler's arguments and this error will likely be gone.
Next. The only flags for g++ that could maybe make it compile your code are -fms-extensions and -fvisibility-ms-compat. Anonymous structs are a non-standard extension that Microsoft added to their compiler. Sorry, right now I can't test it, but I think that would do the trick.
And now some extras.
typedef
structs in C++ — if you named your structs, you can refer to them using that name as type.public
here. Classes, however, are private by default.Hope that this will help you at least somehow.
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