如何用另一个模板 function（特别是 glm::dot）包装模板 function？

Question

I'm using the glm math library, which offers many vector/matrix structs and operations (for use in graphics). It has types for many different vector sizes ( vec2 , vec3 , vec4 , etc...) and also a really clean API to do general operations on them, regardless of size ( dot(a,b) , length(a) , etc...).

One function I would like is to determine the "length squared" of a vector (as it's computationally much cheaper to compare lengths this way), which is essentially this function: float lengthSquared(v) { return glm::dot(v,v); } float lengthSquared(v) { return glm::dot(v,v); }

I'd like to create such a function: how might I go about doing it?

The template signature for dot is as follows:

template <class T, glm::qualifier Q>
T dot(const glm::qua<T,Q> &x, const glm::qua<T,Q> &y)

So my best attempt to wrap is is as follows:

template <class T, glm::qualifier Q>
T lengthSquared(const glm::qua<T,Q> &x)
{ return glm::dot(x,x); }

But I get many errors including 'lengthSquared': no matching overloaded function found (when calling it with a vec2 ), and [signature here]: could not deduce template argument for 'const glm::qua<T,Q> &' from 'glm::vec2' .

I don't really understand how template "qualifiers" work, so I'm flying a bit blind here.

Thanks!

edit: here's the declaration of vec2 : typedef glm::vec<2,float,glm::packed_highp> glm::vec2; and here's a sample call to lengthSquared : vec2 x = {0.5,0.5}; float ls = lengthSquared(x); vec2 x = {0.5,0.5}; float ls = lengthSquared(x);

Answer 1

Your function definition is:

template <class T, glm::qualifier Q>
T lengthSquared(const glm::qua<T,Q> &x)
{ return glm::dot(x,x); }

but you are calling this function with an argument of type glm::vec<2,float,glm::packed_highp> .

Instead, you can write the function like this:

template <class T>
auto lengthSquared(const T &x)
{ return glm::dot(x,x); }

and let the compiler deduce both the argument type, and the return type.

Answer 2

Even though it seemingly doesn't work for you I post a simple C++20 alternative that is supported by current versions of GCC and Clang:

auto lengthSquared(const auto &v) { return glm::dot(v,v); }