Example showing various methods of creating windows

- ui.window(...).build() versus ui.window.begin()
- ui.child_window(...)

imgui-examples/examples/creating_windows.rs

@@ -0,0 +1,69 @@
+mod support;
+
+fn main() {
+    let system = support::init(file!());
+
+    system.main_loop(move |_, ui| {
+        // If we don't explicitly create a window before creating some kind of widget, then Dear Imgui will automatically create one
+        ui.text("This text will appear in a default window titled 'Debug'");
+
+        // However, in almost all cases it's best to make a window, so it has a useful title etc
+
+        // imgui-rs has two main methods of creating windows (and these same approaches
+        // apply to many other widgets). First, callback based:
+
+        ui.window("My window via callback")
+        .build(||{
+            ui.text("This content appears in a window");
+
+            // Everything in this callback appears in the window, like this button:
+            ui.button("This button");
+        });
+
+        // Often the callback approach is most convenient, however occasionally the callbacks can be hard to use.
+        // In this case, there is the "token based" approach. You call a method and get a "window token",
+        // everything that happens until the token is dropped is included in the window this is more-or-less how
+        // the Dear ImGui C++ API works)
+        
+        // Here we (maybe) get a window token:
+        let window_token = ui.window("Token based window").begin();
+        if let Some(_t) = window_token {
+            // If the token is Some(...) then the window contents are visible, so we need to draw them!
+            ui.text("Window contents!")
+        }
+
+        // Here we create a window with a specific size, and force it to always have a vertical scrollbar visible
+        ui.window("Big complex window")
+        .size([200.0, 100.0], imgui::Condition::FirstUseEver)
+        .always_vertical_scrollbar(true)
+        .build(||{
+            ui.text("Imagine something complicated here..");
+
+            // Note you can create windows inside other windows, however, they both appear as separate windows.
+            // For example, somewhere deep inside a complex window, we can quickly create a widget to display a
+            // variable, like a graphical "debug print"
+            ui.window("Confusion").build(||{
+                ui.text(format!("Some variable: {:?}", ui.io().mouse_pos))
+            })
+        });
+
+        // If you want to nest windows inside other windows, you can a "child window".
+        // This is essentially a scrollable area, with all the same properties as a regular window
+        ui.window("Parent window").build(||{
+            ui.child_window("Child window")
+            .size([100.0, 100.0])
+            .build(||{
+                for _ in 0..10 {
+                    ui.text("Lines and");
+                }
+            });
+            ui.child_window("Second child window")
+            .size([100.0, 100.0])
+            .build(||{
+                for _ in 0..10 {
+                    ui.text("More and");
+                }
+            });
+        });
+    });
+}