Add more example for colors.

examples/dom/CMakeLists.txt

@@ -21,6 +21,7 @@ example(style_bold)
 example(style_color)
 example(color_truecolor_RGB)
 example(color_truecolor_HSV)
+example(color_info_palette256)
 example(style_dim)
 example(style_gallery)
 example(style_inverted)

examples/dom/color_info_palette256.cpp

@@ -0,0 +1,83 @@
+// 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>
+#include <ftxui/screen/screen.hpp>
+#include <algorithm>
+#include <ftxui/screen/terminal.hpp>
+#include <ftxui/screen/color_info.hpp>
+#include "ftxui/screen/string.hpp"
+#include <iostream>
+
+int main(int argc, const char* argv[]) {
+  using namespace ftxui;
+
+  // Acquire the color information for the palette256.
+  std::vector<ColorInfo> info_gray;
+  std::vector<ColorInfo> info_color;
+  for (int i = 0; i < 256; ++i) {
+    ColorInfo info = GetColorInfo(Color::Palette256(i));
+    if (info.saturation == 0)
+      info_gray.push_back(info);
+    else
+      info_color.push_back(info);
+  }
+
+  // Sort info_color by hue.
+  std::sort(
+      info_color.begin(), info_color.end(),
+      [](const ColorInfo& A, const ColorInfo& B) { return A.hue < B.hue; });
+
+  // Make 8 colums, one gray and seven colored.
+  std::vector<std::vector<ColorInfo>> info_columns(8);
+  info_columns[0] = info_gray;
+  for (int i = 0; i < info_color.size(); ++i) {
+    info_columns[1 + 7 * i / info_color.size()].push_back(info_color[i]);
+  }
+
+  // Minimize discontinuities for every columns.
+  for (auto& column : info_columns) {
+    std::sort(column.begin(), column.end(),
+              [](const ColorInfo& A, const ColorInfo& B) {
+                return A.value < B.value;
+              });
+    for (int i = 0; i < column.size() - 1; ++i) {
+      int best_index = i + 1;
+      int best_distance = 255 * 255 * 3;
+      for (int j = i + 1; j < column.size(); ++j) {
+        int dx = column[i].red - column[j].red;
+        int dy = column[i].green - column[j].green;
+        int dz = column[i].blue - column[j].blue;
+        int distance = dx * dx + dy * dy + dz * dz;
+        if (best_distance > distance) {
+          best_distance = distance;
+          best_index = j;
+        }
+      }
+      std::swap(column[i+1], column[best_index]);
+    }
+  }
+
+  // Draw every columns
+  Elements columns_elements;
+  for(auto& column : info_columns) {
+    Elements column_elements;
+    for(auto& it : column) {
+      column_elements.push_back(hbox({
+        text(L"     ") | bgcolor(Color(Color::Palette256(it.index))),
+        text(to_wstring(std::string(it.name))),
+      }));
+    }
+    columns_elements.push_back(vbox(std::move(column_elements)));
+  }
+  auto document = hbox(std::move(columns_elements));
+
+  auto screen =
+      Screen::Create(Dimension::Full(), Dimension::Fit(document));
+  Render(screen, document);
+
+  std::cout << screen.ToString();
+
+  return 0;
+}