Refactor ruin_app, add some README files, minor usability in reactivity

lib/ruin_app/src/primitives/button.rs

@@ -0,0 +1,61 @@
+use std::rc::Rc;
+
+use ruin_ui::{CursorIcon, Edges, Element, RoutedPointerEvent};
+
+use crate::context::allocate_element_id;
+use crate::input::PressHandler;
+use crate::primitives::ContainerProps;
+use crate::text_style::{pop_text_style, push_text_style};
+use crate::view::{Children, View};
+use crate::surfaces;
+
+pub struct ButtonBuilder {
+    pub(crate) props: ContainerProps,
+    pub(crate) on_press: Option<PressHandler>,
+}
+
+pub fn button() -> ButtonBuilder {
+    ButtonBuilder {
+        props: ContainerProps::new(
+            Element::column()
+                .padding(Edges::symmetric(14.0, 10.0))
+                .background(surfaces::interactive())
+                .corner_radius(10.0)
+                .cursor(CursorIcon::Pointer)
+                .focusable(true),
+        ),
+        on_press: None,
+    }
+}
+
+impl ButtonBuilder {
+    impl_props_methods!();
+
+    pub fn on_press(mut self, handler: impl Fn(&RoutedPointerEvent) + 'static) -> Self {
+        self.on_press = Some(Rc::new(handler));
+        self
+    }
+
+    pub fn text_style(mut self, style: crate::text_style::PartialTextStyle) -> Self {
+        self.props = self.props.text_style(style);
+        self
+    }
+
+    pub fn children(mut self, children: impl Children) -> View {
+        let id = allocate_element_id();
+        self.props.element = self.props.element.id(id);
+        let had_style = self.props.partial_text_style.is_some();
+        if let Some(style) = self.props.partial_text_style.take() {
+            push_text_style(style);
+        }
+        let children_views = children.into_views();
+        if had_style {
+            pop_text_style();
+        }
+        let view = View::from_container(self.props.element, children_views);
+        match self.on_press {
+            Some(handler) => view.with_press_handler(id, handler),
+            None => view,
+        }
+    }
+}