add query context (#400)

examples/tui_colorpicker.rs

@@ -0,0 +1,27 @@
+use dioxus::prelude::*;
+use dioxus_tui::query::Query;
+use dioxus_tui::Size;
+
+fn main() {
+    dioxus::tui::launch(app);
+}
+
+fn app(cx: Scope) -> Element {
+    let hue = use_state(&cx, || 0.0);
+    let brightness = use_state(&cx, || 0.0);
+    let tui_query: Query = cx.consume_context().unwrap();
+    cx.render(rsx! {
+        div{
+            width: "100%",
+            background_color: "hsl({hue}, 70%, {brightness}%)",
+            onmousemove: move |evt| {
+                let node = tui_query.get(cx.root_node().mounted_id());
+                let Size{width, height} = node.size().unwrap();
+                let pos = evt.data.element_coordinates();
+                hue.set((pos.x as f32/width as f32)*255.0);
+                brightness.set((pos.y as f32/height as f32)*100.0);
+            },
+            "hsl({hue}, 70%, {brightness}%)",
+        }
+    })
+}