Add Box::IsEmpty()

CHANGELOG.md

@@ -29,6 +29,9 @@ current (development)
   reflecting the current scroll position. Proposed by @ibrahimnasson in
   [issue 752](https://github.com/ArthurSonzogni/FTXUI/issues/752)
 
+### Screen
+- Feature: Add `Box::IsEmpty()`.
+
 ### Build
 - Support for cmake's "unity/jumbo" builds. Fixed by @ClausKlein.
 

include/ftxui/screen/box.hpp

@@ -15,7 +15,7 @@ struct Box {
   static auto Intersection(Box a, Box b) -> Box;
   static auto Union(Box a, Box b) -> Box;
   bool Contain(int x, int y) const;
-  int Area() const noexcept;
+  bool IsEmpty();
   bool operator==(const Box& other) const;
   bool operator!=(const Box& other) const;
 };

src/ftxui/dom/canvas.cpp

@@ -850,8 +850,9 @@ void Canvas::DrawImage(int x,
     y = 0;
   }
 
-  if (crop.Area() == 0)
+  if (crop.IsEmpty()) {
     return;
+  }
 
   const auto xend = x + crop.x_max - crop.x_min;
   const auto yend = y + crop.y_max - crop.y_min;

src/ftxui/screen/box.cpp

@@ -39,11 +39,10 @@ bool Box::Contain(int x, int y) const {
          y_max >= y;
 }
 
-/// @return the are of the box
+/// @return whether the box is empty.
 /// @ingroup screen
-int Box::Area() const noexcept {
-  const auto area = (x_max - x_min) * (y_max - y_min);
-  return area < 0 ? 0 : area;
+bool Box::IsEmpty() {
+  return x_min > x_max || y_min > y_max;
 }
 
 /// @return whether |other| is the same as |this|