but if you come from C++ you might be disappointed by the performance,

That's true, but probably not to the extent you imagine. The OpenGL module has "comparable" performance to C, according to these benchmarks: http://graphcomp.com/opengl/index.cgi?v=0111s3B1&r=s3m3.

I second the comments about Tk and Wx. You might also like to look at GtkPerl (it's cross-platform).

The performance of the library itself will be comparable, yes. But if you want to do some more involved calculations (say e.g. precise collision detection) in Perl, it may slow down the program substantially. Perl is just not meant for that. But we are lucky in the way that Perl allows for Modules written in C and even writing single subroutines in C or C++ quite painlessly via Inline::C(++).