Fix: Forward gridbox selected box. (#408)

This was discovered in:
https://github.com/ArthurSonzogni/FTXUI/issues/407

CHANGELOG.md

@@ -7,6 +7,9 @@ current (development)
 ### DOM
 - Bugfix: Fix `focus`/`select` when the `vbox`/`hbox`/`dbox` contains a
   `flexbox`
+- Bugfix: Fix the selected/focused area. It used to be 1 cell larger/longer than
+  requested
+- Bugfix: Forward the selected/focused area from the child in gridbox.
 
 ### Screen
 - Feature: add `Box::Union(a,b) -> Box`

src/ftxui/dom/flexbox_test.cpp

@@ -449,9 +449,9 @@ TEST(FlexboxTest, Focus) {
   Screen screen(1, 3);
   Render(screen, document);
   EXPECT_EQ(screen.ToString(),
-            "7\r\n"
             "-\r\n"
-            "8"
+            "7\r\n"
+            "-"
             );
 }
 

src/ftxui/dom/frame.cpp

@@ -24,8 +24,8 @@ class Select : public Node {
     auto& selected_box = requirement_.selected_box;
     selected_box.x_min = 0;
     selected_box.y_min = 0;
-    selected_box.x_max = requirement_.min_x;
-    selected_box.y_max = requirement_.min_y;
+    selected_box.x_max = requirement_.min_x - 1;
+    selected_box.y_max = requirement_.min_y - 1;
     requirement_.selection = Requirement::SELECTED;
   };
 

src/ftxui/dom/gridbox.cpp

@@ -13,6 +13,23 @@
 namespace ftxui {
 class Screen;
 
+namespace {
+
+// Accumulate the values of a list U[n] into v[n]. So that:
+// V[0] = 0;
+// V[n+1] = v[n] + U[n]
+// return the sum of U[n].
+int Integrate(std::vector<int>& elements) {
+  int accu = 0;
+  for (auto& i : elements) {
+    int old_accu = accu;
+    accu += i;
+    i = old_accu;
+  }
+  return accu;
+}
+}
+
 class GridBox : public Node {
  public:
   explicit GridBox(std::vector<Elements> lines) : lines_(std::move(lines)) {
@@ -38,35 +55,37 @@ class GridBox : public Node {
     for (auto& line : lines_) {
       for (auto& cell : line) {
         cell->ComputeRequirement();
+      }
+    }
 
-        // Determine focus based on the focused child.
-        if (requirement_.selection >= cell->requirement().selection) {
+    // Compute the size of each columns/row.
+    std::vector<int> size_x(x_size, 0);
+    std::vector<int> size_y(y_size, 0);
+    for (int x = 0; x < x_size; ++x) {
+      for (int y = 0; y < y_size; ++y) {
+        size_x[x] = std::max(size_x[x], lines_[y][x]->requirement().min_x);
+        size_y[y] = std::max(size_y[y], lines_[y][x]->requirement().min_y);
+      }
+    }
+
+    requirement_.min_x = Integrate(size_x);
+    requirement_.min_y = Integrate(size_y);
+
+    // Forward the selected/focused child state:
+    requirement_.selection = Requirement::NORMAL;
+    for (int x = 0; x < x_size; ++x) {
+      for (int y = 0; y < y_size; ++y) {
+        if (requirement_.selection >= lines_[y][x]->requirement().selection) {
           continue;
         }
-        requirement_.selection = cell->requirement().selection;
-        requirement_.selected_box = cell->requirement().selected_box;
-        requirement_.selected_box.x_min += requirement_.min_x;
-        requirement_.selected_box.x_max += requirement_.min_x;
+        requirement_.selection = lines_[y][x]->requirement().selection;
+        requirement_.selected_box = lines_[y][x]->requirement().selected_box;
+        requirement_.selected_box.x_min += size_x[x];
+        requirement_.selected_box.x_max += size_x[x];
+        requirement_.selected_box.y_min += size_y[y];
+        requirement_.selected_box.y_max += size_y[y];
       }
     }
-
-    // Work on the x-axis.
-    for (int x = 0; x < x_size; ++x) {
-      int min_x = 0;
-      for (int y = 0; y < y_size; ++y) {
-        min_x = std::max(min_x, lines_[y][x]->requirement().min_x);
-      }
-      requirement_.min_x += min_x;
-    }
-
-    // Work on the y-axis.
-    for (int y = 0; y < y_size; ++y) {
-      int min_y = 0;
-      for (int x = 0; x < x_size; ++x) {
-        min_y = std::max(min_y, lines_[y][x]->requirement().min_y);
-      }
-      requirement_.min_y += min_y;
-    }
   }
 
   void SetBox(Box box) override {

src/ftxui/dom/gridbox_test.cpp

@@ -596,6 +596,25 @@ TEST(GridboxTest, MissingCells) {
             "                    ");
 }
 
+TEST(GridboxTest, Focus) {
+  auto root = gridbox({
+      {cell("1"), cell("2"), cell("3"), cell("4")},
+      {cell("5"), cell("6"), cell("7"), cell("8")},
+      {cell("9"), cell("10"), cell("11"), cell("12")},
+      {cell("13"), cell("14") | focus, cell("15"), cell("16")},
+      {cell("17"), cell("18"), cell("19"), cell("20")},
+  });
+
+  root |= frame;
+
+  Screen screen(4, 3);
+  Render(screen, root);
+  EXPECT_EQ(screen.ToString(),
+            "╭──╮\r\n"
+            "│14│\r\n"
+            "╰──╯");
+}
+
 }  // namespace ftxui
 
 // Copyright 2020 Arthur Sonzogni. All rights reserved.