Add support for password for input element. (#158)

This fixes:
https://github.com/ArthurSonzogni/FTXUI/issues/139

CC:@Creapermann

examples/component/input.cpp

@@ -10,23 +10,31 @@
 int main(int argc, const char* argv[]) {
   using namespace ftxui;
 
-  std::wstring first_name_;
-  std::wstring last_name_;
+  std::wstring first_name;
+  std::wstring last_name;
+  std::wstring password;
 
-  Component input_first_name_ = Input(&first_name_, "first name");
-  Component input_last_name_ = Input(&last_name_, "last name");
+
+  Component input_first_name = Input(&first_name, "first name");
+  Component input_last_name = Input(&last_name, "last name");
+
+  InputOption password_option;
+  password_option.password = true;
+  Component input_password = Input(&password, "password", password_option);
 
   auto component = Container::Vertical({
-      input_first_name_,
-      input_last_name_,
+      input_first_name,
+      input_last_name,
+      input_password,
   });
 
   auto renderer = Renderer(component, [&] {
     return vbox({
-               text(L"Hello " + first_name_ + L" " + last_name_),
+               text(L"Hello " + first_name + L" " + last_name),
                separator(),
-               hbox({text(L" First name  : "), input_first_name_->Render()}),
-               hbox({text(L" Last name   : "), input_last_name_->Render()}),
+               hbox(text(L" First name : "), input_first_name->Render()),
+               hbox(text(L" Last name  : "), input_last_name->Render()),
+               hbox(text(L" Password   : "), input_password->Render()),
            }) |
            border;
   });

include/ftxui/component/component_options.hpp

@@ -50,6 +50,9 @@ struct InputOption {
   /// Called when the user presses enter.
   std::function<void()> on_enter = [] {};
 
+  /// Obscure the input content using '*'.
+  bool password = false;
+
   Ref<int> cursor_position = 0;
 };
 

include/ftxui/screen/screen.hpp

@@ -45,9 +45,7 @@ struct Pixel {
 /// @brief Define how the Screen's dimensions should look like.
 /// @ingroup screen
 struct Dimension {
-  /// coucou
   static Dimension Fixed(int);
-  /// @brief coucou
   static Dimension Fit(Element&);
   static Dimension Full();
 

src/ftxui/component/input.cpp

@@ -30,13 +30,18 @@ class InputBase : public ComponentBase {
 
   // Component implementation:
   Element Render() override {
+    std::wstring password_content;
+    if (option_->password)
+      password_content = std::wstring(content_->size(), U'•');
+    std::wstring& content = option_->password ? password_content : *content_;
+
     cursor_position() =
-        std::max(0, std::min<int>(content_->size(), cursor_position()));
+        std::max(0, std::min<int>(content.size(), cursor_position()));
     auto main_decorator = flex | size(HEIGHT, EQUAL, 1);
     bool is_focused = Focused();
 
     // placeholder.
-    if (content_->size() == 0) {
+    if (content.size() == 0) {
       if (is_focused)
         return text(*placeholder_) | focus | dim | inverted | main_decorator |
                reflect(input_box_);
@@ -46,15 +51,15 @@ class InputBase : public ComponentBase {
 
     // Not focused.
     if (!is_focused)
-      return text(*content_) | main_decorator | reflect(input_box_);
+      return text(content) | main_decorator | reflect(input_box_);
 
-    std::wstring part_before_cursor = content_->substr(0, cursor_position());
-    std::wstring part_at_cursor = cursor_position() < (int)content_->size()
-                                      ? content_->substr(cursor_position(), 1)
+    std::wstring part_before_cursor = content.substr(0, cursor_position());
+    std::wstring part_at_cursor = cursor_position() < (int)content.size()
+                                      ? content.substr(cursor_position(), 1)
                                       : L" ";
     std::wstring part_after_cursor =
-        cursor_position() < (int)content_->size() - 1
-            ? content_->substr(cursor_position() + 1)
+        cursor_position() < (int)content.size() - 1
+            ? content.substr(cursor_position() + 1)
             : L"";
     auto focused = is_focused ? focus : select;
 

src/ftxui/component/input_test.cpp

@@ -35,6 +35,34 @@ TEST(InputTest, Type) {
   input->OnEvent(Event::Character('b'));
   EXPECT_EQ(content, L"ab");
   EXPECT_EQ(option.cursor_position(), 2u);
+
+  auto document = input->Render();
+  auto screen = Screen::Create(Dimension::Fit(document));
+  Render(screen, document);
+  EXPECT_EQ(screen.PixelAt(0, 0).character, L"a");
+  EXPECT_EQ(screen.PixelAt(1, 0).character, L"b");
+}
+
+TEST(InputTest, TypePassword) {
+  std::wstring content;
+  std::wstring placeholder;
+  auto option = InputOption();
+  option.password = true;
+  Component input = Input(&content, &placeholder, &option);
+
+  input->OnEvent(Event::Character('a'));
+  EXPECT_EQ(content, L"a");
+  EXPECT_EQ(option.cursor_position(), 1u);
+
+  input->OnEvent(Event::Character('b'));
+  EXPECT_EQ(content, L"ab");
+  EXPECT_EQ(option.cursor_position(), 2u);
+
+  auto document = input->Render();
+  auto screen = Screen::Create(Dimension::Fit(document));
+  Render(screen, document);
+  EXPECT_EQ(screen.PixelAt(0, 0).character, L"•");
+  EXPECT_EQ(screen.PixelAt(1, 0).character, L"•");
 }
 
 TEST(InputTest, Arrow) {