libui - usage

main.cc

#include <ui-app.h>
#include <ui-window.h>

using namespace ui;

int main(int argc, const char *argv[]) {
  App app;

  Window mainWindow({{10,0}, {800, 600}});

  /* close app with window */
  mainWindow.setCloseBehavior(kWindowCloseBehavior_AppShouldExit);

  View view1({{10, 10}, {150, 150}});
  view1.setBackgroundColor({1, 0, 0});

  View view2({{5, 5}, {50, 50}});
  view2.setBackgroundColor({1, 1, 1});

  /* add view2 to view1 */
  view1.addSubview(view2);

  /* add view 1 to window's content view */
  mainWindow.contentView()->addSubview(view1);

  View view3({{10, 10}, {30, 30}});
  view3.setBackgroundColor({0, 0, 1});

  view2.addSubview(view3);
  mainWindow.show();

  app.run();

  return 0;
}

Win32 (Wİndows 10):

Cocoa (macOS 10.12)