Fix ScreenInteractive::FixedSize screen stomps on the history terminal output (#1064)

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

CHANGELOG.md

@@ -25,6 +25,10 @@ Next
   ```
   Thanks @mikomikotaishi for PR #1015.
 
+### Component
+- Fix ScreenInteractive::FixedSize screen stomps on the preceding terminal
+  output. Thanks @zozowell in #1064.
+
 
 6.1.9 (2025-05-07)
 ------------

include/ftxui/component/screen_interactive.hpp

@@ -10,7 +10,6 @@
 #include <memory>                        // for shared_ptr
 #include <string>                        // for string
 #include <thread>                        // for thread
-#include <variant>                       // for variant
 
 #include "ftxui/component/animation.hpp"       // for TimePoint
 #include "ftxui/component/captured_mouse.hpp"  // for CapturedMouse
@@ -105,12 +104,12 @@ class ScreenInteractive : public Screen {
     Fullscreen,
     TerminalOutput,
   };
-  Dimension dimension_ = Dimension::Fixed;
-  bool use_alternative_screen_ = false;
-  ScreenInteractive(int dimx,
+  ScreenInteractive(Dimension dimension,
+                    int dimx,
                     int dimy,
-                    Dimension dimension,
                     bool use_alternative_screen);
+  const Dimension dimension_;
+  const bool use_alternative_screen_;
 
   bool track_mouse_ = true;
 
@@ -129,6 +128,7 @@ class ScreenInteractive : public Screen {
   int cursor_x_ = 1;
   int cursor_y_ = 1;
 
+  std::uint64_t frame_count_ = 0;
   bool mouse_captured = false;
   bool previous_frame_resized_ = false;
 

src/ftxui/component/screen_interactive.cpp

@@ -346,9 +346,9 @@ void AnimationListener(std::atomic<bool>* quit, Sender<Task> out) {
 
 }  // namespace
 
-ScreenInteractive::ScreenInteractive(int dimx,
+ScreenInteractive::ScreenInteractive(Dimension dimension,
+                                     int dimx,
                                      int dimy,
-                                     Dimension dimension,
                                      bool use_alternative_screen)
     : Screen(dimx, dimy),
       dimension_(dimension),
@@ -359,10 +359,10 @@ ScreenInteractive::ScreenInteractive(int dimx,
 // static
 ScreenInteractive ScreenInteractive::FixedSize(int dimx, int dimy) {
   return {
+      Dimension::Fixed,
       dimx,
       dimy,
-      Dimension::Fixed,
-      false,
+      /*use_alternative_screen=*/false,
   };
 }
 
@@ -379,11 +379,12 @@ ScreenInteractive ScreenInteractive::Fullscreen() {
 /// content might mess up with the terminal content.
 // static
 ScreenInteractive ScreenInteractive::FullscreenPrimaryScreen() {
+  auto terminal = Terminal::Size();
   return {
-      0,
-      0,
-      Dimension::Fullscreen,
-      false,
+    Dimension::Fullscreen,
+    terminal.dimx,
+    terminal.dimy,
+    /*use_alternative_screen=*/false,
   };
 }
 
@@ -391,30 +392,37 @@ ScreenInteractive ScreenInteractive::FullscreenPrimaryScreen() {
 /// alternate screen buffer to avoid messing with the terminal content.
 // static
 ScreenInteractive ScreenInteractive::FullscreenAlternateScreen() {
+  auto terminal = Terminal::Size();
   return {
-      0,
-      0,
       Dimension::Fullscreen,
-      true,
+      terminal.dimx,
+      terminal.dimy,
+      /*use_alternative_screen=*/true,
   };
 }
 
+/// Create a ScreenInteractive whose width match the terminal output width and
+/// the height matches the component being drawn.
 // static
 ScreenInteractive ScreenInteractive::TerminalOutput() {
+  auto terminal = Terminal::Size();
   return {
-      0,
-      0,
       Dimension::TerminalOutput,
-      false,
+      terminal.dimx,
+      terminal.dimy, // Best guess.
+      /*use_alternative_screen=*/false,
   };
 }
 
+/// Create a ScreenInteractive whose width and height match the component being
+/// drawn.
 // static
 ScreenInteractive ScreenInteractive::FitComponent() {
+  auto terminal = Terminal::Size();
   return {
-      0,
-      0,
       Dimension::FitComponent,
+      terminal.dimx, // Best guess.
+      terminal.dimy, // Best guess.
       false,
   };
 }
@@ -921,7 +929,7 @@ void ScreenInteractive::Draw(Component component) {
       break;
   }
 
-  const bool resized = (dimx != dimx_) || (dimy != dimy_);
+  const bool resized = frame_count_ == 0 || (dimx != dimx_) || (dimy != dimy_);
   ResetCursorPosition();
   std::cout << ResetPosition(/*clear=*/resized);
 
@@ -1004,6 +1012,7 @@ void ScreenInteractive::Draw(Component component) {
   Flush();
   Clear();
   frame_valid_ = true;
+  frame_count_++;
 }
 
 // private

src/ftxui/component/screen_interactive_test.cpp

@@ -10,9 +10,57 @@
 #include "ftxui/component/screen_interactive.hpp"
 #include "ftxui/dom/elements.hpp"  // for text, Element
 
+#if defined(__unix__)
+#include <fcntl.h>
+#include <unistd.h>
+#include <array>
+#include <cstdio>
+#include <ftxui/component/loop.hpp>
+#include <string>
+#endif
+
 namespace ftxui {
 
 namespace {
+#if defined(__unix__)
+
+// Capture the standard output (stdout) to a string.
+class StdCapture {
+ public:
+  explicit StdCapture(std::string* captured)
+      : captured_(captured) {
+    if (pipe(pipefd_) != 0) return;
+    old_stdout_ = dup(fileno(stdout));
+    fflush(stdout);
+    dup2(pipefd_[1], fileno(stdout));
+    close(pipefd_[1]);  // Close the write end in the parent
+  }
+
+  ~StdCapture() {
+    fflush(stdout);
+    dup2(old_stdout_, fileno(stdout));
+    close(old_stdout_);
+
+    char buffer[1024];
+    ssize_t count;
+    while ((count = read(pipefd_[0], buffer, sizeof(buffer))) > 0) {
+      captured_->append(buffer, count);
+    }
+
+    close(pipefd_[0]);
+  }
+
+  StdCapture(const StdCapture&) = delete;
+  StdCapture& operator=(const StdCapture&) = delete;
+
+ private:
+  int pipefd_[2]{-1, -1};
+  int old_stdout_{-1};
+  std::string* const captured_;
+};
+
+#endif
+
 bool TestSignal(int signal) {
   int called = 0;
   // The tree of components. This defines how to navigate using the keyboard.
@@ -131,4 +179,69 @@ TEST(ScreenInteractive, CtrlC_NotForced) {
   ASSERT_GE(ctrl_c_count, 50);
 }
 
+// Regression test for:
+// https://github.com/ArthurSonzogni/FTXUI/pull/1064/files
+TEST(ScreenInteractive, FixedSizeInitialFrame) {
+#if defined(__unix__)
+  std::string output;
+  {
+    auto capture = StdCapture(&output);
+
+    auto screen = ScreenInteractive::FixedSize(2, 2);
+    auto component = Renderer([&] {
+      return text("AB");
+    });
+
+    Loop loop(&screen, component);
+    loop.RunOnce();
+  }
+  using namespace std::string_view_literals;
+
+  auto expected =
+      // Install the ScreenInteractive.
+      "\0"           // Flush stdout.
+      "\x1BP$q q"    // Set cursor shape to 1 (block).
+      "\x1B\\"       // Reset cursor position.
+      "\x1B[?7l"     // Disable line wrapping.
+      "\x1B[?1000h"  // Enable mouse tracking.
+      "\x1B[?1003h"  // Enable mouse motion tracking.
+      "\x1B[?1015h"  // Enable mouse wheel tracking.
+      "\x1B[?1006h"  // Enable SGR mouse tracking.
+      "\0"           // Flush stdout.
+
+      // Reset the screen.
+      "\r"       // Reset cursor position.
+      "\x1B[2K"  // Clear the line.
+      "\x1B[1A"  // Move cursor up one line.
+      "\x1B[2K"  // Clear the line.
+
+      // Print the document.
+      "AB\r\n"  // Print "AB" and move to the next line.
+      "  "      // Print two spaces to fill the line.
+
+      // Set cursor position.
+      "\x1B[1D"    // Move cursor left one character.
+      "\x1B[?25l"  // Hide cursor.
+
+      // Flush
+      "\0"  // Flush stdout.
+
+      // Uninstall the ScreenInteractive.
+      "\x1B[1C"      // Move cursor right one character.
+      "\x1B[?1006l"  // Disable SGR mouse tracking.
+      "\x1B[?1015l"  // Disable mouse wheel tracking.
+      "\x1B[?1003l"  // Disable mouse motion tracking.
+      "\x1B[?1000l"  // Disable mouse tracking.
+      "\x1B[?7h"     // Enable line wrapping.
+      "\x1B[?25h"    // Show cursor.
+      "\x1B[1 q"     // Set cursor shape to 1 (block).
+      "\0"           // Flush stdout.
+
+      // Skip one line to avoid the prompt to be printed over the last drawing.
+      "\r\n"sv;
+  ASSERT_EQ(expected, output);
+#endif
+
+}
+
 }  // namespace ftxui