Allow Limbo to work on windows.

[nickanthony-dgl]

This PR makes 2 minor changes to allow Limbo to compile on a Windows machine. These changes are guarded by the #ifdef _WIN32 preprocessor so they will not affect non-Windows builds.

• In "limbo/model/gp.hpp" includes "corecrt_math_defines.h" so that the M_PI preprocessor define will be defined
• In "limbo/tools/sys.hpp" "windows.h" is included instead of "unistd.h" and the "GetComputerNameA" function is used instead of "unistd.h"'s "gethostname" function.

[costashatz]

@nickanthony-dgl thanks a lot for this PR. Great that limbo works in Windows as well with so little changes :) See one minor improvement requested. Thanks again! 😄

[costashatz]

I think I prefer the following alternative:

#define _USE_MATH_DEFINES
#include <cmath>

[nickanthony-dgl]

That doesn't appear to be working for me, I get "M_PI": identifier not found. I think the issue is that if <cmath> has already been included somewhere earlier in the compilation then:

#define _USE_MATH_DEFINES
#include <cmath>

will have no effect. You have to make sure that #define _USE_MATH_DEFINES happens before the first inclusion of <cmath> which can be difficult for a header-only library.

This same issue is discussed here and here

How would you feel about skipping the use of the M_PI preprocessor constant altogether and instead use something like:

namespace limbo {
  constexpr double PI = 3.14159265359;
  ...

[costashatz]

Most probably you need to put it here: https://github.com/resibots/limbo/blob/master/src/limbo/tools/math.hpp#L50. If this is not working, please enabling editing by admins for the PR and I will make the define from waf to be globally defined.

[costashatz]

How would you feel about skipping the use of the M_PI preprocessor constant altogether and instead use something like

My issue with that is that we would need to define a bigger set of constants, otherwise we are inconsistent. And this is a Windows issue. We will find a way to by-pass it.

[nickanthony-dgl]

putting it in math.hpp didn't work but putting it in bo_base.hpp (the only place I see where gp.hpp is used) did. Please see the most recent commit.

I will go ahead and enable editing on this PR. Edit: It looks like "Allow edits by maintainers" is already enabled.

[costashatz]

Thanks a lot for the effort! I will try to have a look asap!