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This indeed is the standard solution for C-style windowing libraries - each window provided by the framework can keep some arbitrary cookie - which is most frequently used to hold the actual instance (object) pointer, and it is used in a static method to bounce through to the actual object. And I would call this no-extra-cost as the framework is reserving these 32- (or 64-) bits anyway so no storage cost and you'd have to do something to get back to your actual object anyway.

davidbak
– davidbak

2020-12-19 16:43:04 +00:00
Commented Dec 19, 2020 at 16:43
And while it varies from library to library, some libraries like Python do make it zero-cost. They make the getPointer function into a macro, rather than a real function, removing all of the extra cost.

Cort Ammon
– Cort Ammon

2020-12-19 18:16:41 +00:00
Commented Dec 19, 2020 at 18:16
4

Note that you could avoid the static function by using a lambda as OP tried. glfwSetWindowCloseCallback(mHandle, [](auto window) { static_cast<Window*>(glfwGetWindowUserPointer(wHandle))->onClose(); }) for example.

Christoph
– Christoph

2020-12-19 19:18:48 +00:00
Commented Dec 19, 2020 at 19:18
@Christoph cool. Lambdas didn’t exist in C++ last time I used it.

James McLeod
– James McLeod

2020-12-19 21:41:51 +00:00
Commented Dec 19, 2020 at 21:41
1

Also, in onCloseWrapper it should be Window* w = static_cast<Window*>(glfwGetWindowUserPointer(wHandle)); w->onClose();

user381469
– user381469

2020-12-20 12:29:40 +00:00
Commented Dec 20, 2020 at 12:29

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