Add size(width, height) decorator.

ftxui/src/ftxui/dom/size.cpp

@@ -0,0 +1,35 @@
+#include "ftxui/dom/node.hpp"
+#include "ftxui/dom/elements.hpp"
+
+namespace ftxui::dom {
+
+class Size : public Node {
+ public:
+  Size(Element child, size_t width, size_t height)
+      : Node(unpack(std::move(child))), width_(width), height_(height) {}
+  ~Size() override {}
+  void ComputeRequirement() override {
+    Node::ComputeRequirement();
+    requirement_.min.x = width_;
+    requirement_.min.y = height_;
+    requirement_.flex.x = 0;
+    requirement_.flex.y = 0;
+  }
+
+  void SetBox(Box box) override {
+    Node::SetBox(box);
+    children[0]->SetBox(box);
+  }
+
+ private:
+  size_t width_;
+  size_t height_;
+};
+
+Decorator size(size_t width, size_t height) {
+  return [=](Element e) {
+    return std::make_unique<Size>(std::move(e), width, height);
+  };
+}
+
+};  // namespace ftxui::dom