examples/libs/emscripten/emscripten_mainloop_stub.h - third_party/imgui - Git at Google

 // What does this file solves?
 // - Since Dear ImGui 1.00 we took pride that most of our examples applications had their entire
 //   main-loop inside the main() function. That's because:
 //   - It makes the examples easier to read, keeping the code sequential.
 //   - It permit the use of local variables, making it easier to try things and perform quick
 //     changes when someone needs to quickly test something (vs having to structure the example
 //     in order to pass data around). This is very important because people use those examples
 //     to craft easy-to-past repro when they want to discuss features or report issues.
 //   - It conveys at a glance that this is a no-BS framework, it won't take your main loop away from you.
 //   - It is generally nice and elegant.
 // - However, comes Emscripten... it is a wonderful and magical tech but it requires a "main loop" function.
 // - Only some of our examples would run on Emscripten. Typically the ones rendering with GL or WGPU ones.
 // - I tried to refactor those examples but felt it was problematic that other examples didn't follow the
 //   same layout. Why would the SDL+GL example be structured one way and the SGL+DX11 be structured differently?
 //   Especially as we are trying hard to convey that using a Dear ImGui backend in an *existing application*
 //   should requires only a few dozens lines of code, and this should be consistent and symmetrical for all backends.
 // - So the next logical step was to refactor all examples to follow that layout of using a "main loop" function.
 //   This worked, but it made us lose all the nice things we had...

 // Since only about 3 examples really need to run with Emscripten, here's our solution:
 // - Use some weird macros and capturing lambda to turn a loop in main() into a function.
 // - Hide all that crap in this file so it doesn't make our examples unusually ugly.
 //   As a stance and principle of Dear ImGui development we don't use C++ headers and we don't
 //   want to suggest to the newcomer that we would ever use C++ headers as this would affect
 //   the initial judgment of many of our target audience.
 // - Technique is based on this idea: https://github.com/ocornut/imgui/pull/2492/
 #ifdef __EMSCRIPTEN__
 #include <emscripten.h>
 #include <functional>
 static std::function<void()>            MainLoopForEmscriptenP;
 static void MainLoopForEmscripten()     { MainLoopForEmscriptenP(); }
 #define EMSCRIPTEN_MAINLOOP_BEGIN       MainLoopForEmscriptenP = [&]()
 #define EMSCRIPTEN_MAINLOOP_END         ; emscripten_set_main_loop(MainLoopForEmscripten, 0, true)
 #else
 #define EMSCRIPTEN_MAINLOOP_BEGIN
 #define EMSCRIPTEN_MAINLOOP_END
 #endif
	// What does this file solves?
	// - Since Dear ImGui 1.00 we took pride that most of our examples applications had their entire
	// main-loop inside the main() function. That's because:
	// - It makes the examples easier to read, keeping the code sequential.
	// - It permit the use of local variables, making it easier to try things and perform quick
	// changes when someone needs to quickly test something (vs having to structure the example
	// in order to pass data around). This is very important because people use those examples
	// to craft easy-to-past repro when they want to discuss features or report issues.
	// - It conveys at a glance that this is a no-BS framework, it won't take your main loop away from you.
	// - It is generally nice and elegant.
	// - However, comes Emscripten... it is a wonderful and magical tech but it requires a "main loop" function.
	// - Only some of our examples would run on Emscripten. Typically the ones rendering with GL or WGPU ones.
	// - I tried to refactor those examples but felt it was problematic that other examples didn't follow the
	// same layout. Why would the SDL+GL example be structured one way and the SGL+DX11 be structured differently?
	// Especially as we are trying hard to convey that using a Dear ImGui backend in an existing application
	// should requires only a few dozens lines of code, and this should be consistent and symmetrical for all backends.
	// - So the next logical step was to refactor all examples to follow that layout of using a "main loop" function.
	// This worked, but it made us lose all the nice things we had...

	// Since only about 3 examples really need to run with Emscripten, here's our solution:
	// - Use some weird macros and capturing lambda to turn a loop in main() into a function.
	// - Hide all that crap in this file so it doesn't make our examples unusually ugly.
	// As a stance and principle of Dear ImGui development we don't use C++ headers and we don't
	// want to suggest to the newcomer that we would ever use C++ headers as this would affect
	// the initial judgment of many of our target audience.
	// - Technique is based on this idea: https://github.com/ocornut/imgui/pull/2492/
	#ifdef __EMSCRIPTEN__
	#include <emscripten.h>
	#include <functional>
	static std::function<void()> MainLoopForEmscriptenP;
	static void MainLoopForEmscripten() { MainLoopForEmscriptenP(); }
	#define EMSCRIPTEN_MAINLOOP_BEGIN MainLoopForEmscriptenP = [&]()
	#define EMSCRIPTEN_MAINLOOP_END ; emscripten_set_main_loop(MainLoopForEmscripten, 0, true)
	#else
	#define EMSCRIPTEN_MAINLOOP_BEGIN
	#define EMSCRIPTEN_MAINLOOP_END
	#endif