Add focusPosition[relative](x,y) (#280)

It allows when using inside a frame, to scroll the view toward a
particular position.

This resolves:
https://github.com/ArthurSonzogni/FTXUI/issues/125

CHANGELOG.md

@@ -17,6 +17,13 @@ unreleased (development)
   - `paragraphAlignRight`
   - `paragraphAlignJustify`
 - Add the helper elements based on `flexbox`: `hflow()`, `vflow()`.
+- Add: `focusPositionRelative` and `focusPosition`
+
+### Bug
+
+#### Component 
+- `Input` shouldn't take focus when hovered by the mouse.
+- Modifying `Input`'s during on_enter/on_change event is now working correctly.
 
 ### Bug
 

CMakeLists.txt

@@ -57,6 +57,7 @@ add_library(dom
   src/ftxui/dom/flexbox_config.cpp
   src/ftxui/dom/flexbox_helper.cpp
   src/ftxui/dom/flexbox_helper.hpp
+  src/ftxui/dom/focus.cpp
   src/ftxui/dom/frame.cpp
   src/ftxui/dom/gauge.cpp
   src/ftxui/dom/graph.cpp

examples/component/CMakeLists.txt

@@ -10,6 +10,7 @@ example(gallery)
 example(homescreen)
 example(input)
 example(maybe)
+example(focus)
 example(menu)
 example(menu2)
 example(menu_entries)

examples/component/focus.cpp

@@ -0,0 +1,72 @@
+#include <stddef.h>  // for size_t
+#include <memory>    // for shared_ptr, __shared_ptr_access, allocator
+#include <string>  // for string, basic_string, to_string, operator+, char_traits
+#include <vector>  // for vector
+
+#include "ftxui/component/captured_mouse.hpp"  // for ftxui
+#include "ftxui/component/component.hpp"  // for Radiobox, Vertical, Checkbox, Horizontal, Renderer, ResizableSplitBottom, ResizableSplitRight
+#include "ftxui/component/component_base.hpp"      // for ComponentBase
+#include "ftxui/component/screen_interactive.hpp"  // for ScreenInteractive
+#include "ftxui/dom/elements.hpp"  // for text, window, operator|, vbox, hbox, Element, flexbox, bgcolor, filler, flex, size, border, hcenter, color, EQUAL, bold, dim, notflex, xflex_grow, yflex_grow, HEIGHT, WIDTH
+#include "ftxui/dom/flexbox_config.hpp"  // for FlexboxConfig, FlexboxConfig::AlignContent, FlexboxConfig::JustifyContent, FlexboxConfig::AlignContent::Center, FlexboxConfig::AlignItems, FlexboxConfig::Direction, FlexboxConfig::JustifyContent::Center, FlexboxConfig::Wrap
+#include "ftxui/screen/color.hpp"        // for Color, Color::Black
+
+using namespace ftxui;
+
+Element make_box(int x, int y) {
+  std::string title = "(" + std::to_string(x) + ", " + std::to_string(y) + ")";
+  return text(title) | center | size(WIDTH, EQUAL, 18) |
+         size(HEIGHT, EQUAL, 9) | border |
+         bgcolor(Color::HSV(x * 255 / 15, 255, y * 255 / 15));
+};
+
+Element make_grid() {
+  std::vector<Elements> rows;
+  for (int i = 0; i < 15; i++) {
+    std::vector<Element> cols;
+    for (int j = 0; j < 15; j++) {
+      cols.push_back(make_box(i, j));
+    }
+    rows.push_back(cols);
+  }
+
+  return gridbox(rows);
+};
+
+int main(int argc, const char* argv[]) {
+  float focus_x = 0.0f;
+  float focus_y = 0.0f;
+
+  auto slider_x = Slider("x", &focus_x, 0.f, 1.f, 0.05f);
+  auto slider_y = Slider("y", &focus_y, 0.f, 1.f, 0.05f);
+
+  auto renderer = Renderer(
+      Container::Vertical({
+          slider_x,
+          slider_y,
+      }),
+      [&] {
+        auto title = "focusPositionRelative(" +        //
+                     std::to_string(focus_x) + ", " +  //
+                     std::to_string(focus_y) + ")";    //
+        return vbox({
+                   text(title),
+                   separator(),
+                   slider_x->Render(),
+                   slider_y->Render(),
+                   separator(),
+                   make_grid() | focusPositionRelative(focus_x, focus_y) |
+                       frame | flex,
+               }) |
+               border;
+      });
+
+  auto screen = ScreenInteractive::Fullscreen();
+  screen.Loop(renderer);
+
+  return 0;
+}
+
+// Copyright 2020 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.

include/ftxui/dom/elements.hpp

@@ -68,6 +68,8 @@ Decorator color(Color);
 Decorator bgcolor(Color);
 Element color(Color, Element);
 Element bgcolor(Color, Element);
+Decorator focusPosition(int x, int y);
+Decorator focusPositionRelative(float x, float y);
 
 // --- Layout is
 // Horizontal, Vertical or stacked set of elements.

src/ftxui/dom/focus.cpp

@@ -0,0 +1,103 @@
+#include <memory>   // for make_shared
+#include <utility>  // for move
+
+#include "ftxui/dom/elements.hpp"        // for Element, bold
+#include "ftxui/dom/node.hpp"            // for Node
+#include "ftxui/dom/node_decorator.hpp"  // for NodeDecorator
+#include "ftxui/screen/box.hpp"          // for Box
+#include "ftxui/screen/screen.hpp"       // for Pixel, Screen
+
+namespace ftxui {
+
+namespace {
+
+}  // namespace
+
+/// @brief Used inside a `frame`, this force the view to be scrolled toward a
+/// a given position. The position is expressed in proportion of the requested
+/// size.
+/// 
+/// For instance:
+/// - (0, 0) means that the view is scrolled toward the upper left.
+/// - (1, 0) means that the view is scrolled toward the upper right.
+/// - (0, 1) means that the view is scrolled toward the bottom left.
+/// @ingroup dom
+///
+/// ### Example
+///
+/// ```cpp
+/// Element document = huge_document()
+///   | focusPositionRelative(0.f, 1.f)
+///   | frame;
+/// ```
+Decorator focusPositionRelative(float x, float y) {
+  class Impl : public NodeDecorator {
+   public:
+    Impl(Element child, float x, float y)
+        : NodeDecorator(child), x_(x), y_(y) {}
+
+    void ComputeRequirement() override {
+      NodeDecorator::ComputeRequirement();
+      requirement_.selection = Requirement::Selection::NORMAL;
+
+      Box& box = requirement_.selected_box;
+      box.x_min = requirement_.min_x * x_;
+      box.y_min = requirement_.min_y * y_;
+      box.x_max = requirement_.min_x * x_;
+      box.y_max = requirement_.min_y * y_;
+    }
+
+   private:
+    const float x_;
+    const float y_;
+  };
+
+  return [x, y](Element child) {
+    return std::make_shared<Impl>(std::move(child), x, y);
+  };
+}
+
+/// @brief Used inside a `frame`, this force the view to be scrolled toward a
+/// a given position. The position is expressed in the numbers of cells.
+/// 
+/// @ingroup dom
+///
+/// ### Example
+///
+/// ```cpp
+/// Element document = huge_document()
+///   | focusPosition(10, 10)
+///   | frame;
+/// ```
+Decorator focusPosition(int x, int y) {
+  class Impl : public NodeDecorator {
+   public:
+    Impl(Element child, float x, float y)
+        : NodeDecorator(child), x_(x), y_(y) {}
+
+    void ComputeRequirement() override {
+      NodeDecorator::ComputeRequirement();
+      requirement_.selection = Requirement::Selection::NORMAL;
+
+      Box& box = requirement_.selected_box;
+      box.x_min = x_;
+      box.y_min = y_;
+      box.x_max = x_;
+      box.y_max = y_;
+    }
+
+   private:
+    const int x_;
+    const int y_;
+  };
+
+  return [x, y](Element child) {
+    return std::make_shared<Impl>(std::move(child), x, y);
+  };
+}
+
+}  // namespace ftxui
+
+// Copyright 2020 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.