tui-cs · tig · May 24, 2026 · May 24, 2026 · May 24, 2026 · May 24, 2026
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+# Bug Report: Wide/Fullwidth Character Rendering Causes Display Tearing
+
+## Summary
+
+The terminal incorrectly renders wide (fullwidth) Unicode characters, advancing the cursor by only 1 column instead of the required 2. This causes all subsequent content on the line to shift left, breaking grid alignment and causing display "tearing" in TUI applications.
+
+## Reproduction
+
+```bash
+git clone https://github.com/gui-cs/Terminal.Gui.git
+cd Terminal.Gui/Examples/WideCharRepro
+dotnet run
+```
+
+Or paste this minimal C# program (requires .NET 8+):
+
+<details>
+<summary>Minimal repro (click to expand)</summary>
+
+```csharp
+using System.Text;
+
+Console.OutputEncoding = Encoding.UTF8;
+
+Console.WriteLine ("TEST: Emoji grid (each emoji = 2 columns)");
+Console.WriteLine ("┌──┬──┬──┬──┬──┬──┬──┬──┐");
+Console.WriteLine ("│😀│😁│😂│🤣│😄│😅│😆│😇│");
+Console.WriteLine ("│──│──│──│──│──│──│──│──│");
+Console.WriteLine ("│🐶│🐱│🐭│🐹│🐰│🦊│🐻│🐼│");
+Console.WriteLine ("└──┴──┴──┴──┴──┴──┴──┴──┘");
+Console.WriteLine ();
+Console.WriteLine ("TEST: Column alignment (X should be at column 20)");
+Console.WriteLine ("01234567890123456789X  <- 20 narrow (20×1=20)");
+Console.WriteLine ("😀😁😂😃😄😅😆😇😈😉X  <- 10 emoji  (10×2=20)");
+Console.WriteLine ("你好世界测试宽字符验X  <- 10 CJK    (10×2=20)");
+```
+
+</details>
+
+## Expected Behavior
+
+Each wide character (emoji, CJK ideograph, fullwidth form) should advance the cursor by **2 columns**. Grid separators (`│`) should be vertically aligned:
+
+```
+┌──┬──┬──┬──┬──┬──┬──┬──┐
+│😀│😁│😂│🤣│😄│😅│😆│😇│
+│──│──│──│──│──│──│──│──│
+│🐶│🐱│🐭│🐹│🐰│🦊│🐻│🐼│
+└──┴──┴──┴──┴──┴──┴──┴──┘
+```
+
+The `X` markers should vertically align at column 20:
+```
+01234567890123456789X
+😀😁😂😃😄😅😆😇😈😉X
+你好世界测试宽字符验X
+```
+
+## Actual Behavior
+
+Wide characters advance the cursor by only 1 column. Grids misalign and text overlaps:
+
+```
+┌──┬──┬──┬──┬──┬──┬──┬──┐
+│😀│😁│😂│🤣│😄│😅│😆│😇│   <- shifted left
+│──│──│──│──│──│──│──│──│
+│🐶│🐱│🐭│🐹│🐰│🦊│🐻│🐼│   <- shifted left
+└──┴──┴──┴──┴──┴──┴──┴──┘
+```
+
+## Terminal Compatibility Matrix
+
+| Terminal | Version | OS | Test 1 (Emoji) | Test 2 (CJK) | Test 3 (Mixed) | Test 4 (Grid) | Test 5 (Align) | Status |
+|---------|---------|-----|:-:|:-:|:-:|:-:|:-:|--------|
+| Windows Terminal | 1.22+ | Windows | ✅ | ✅ | ✅ | ✅ | ✅ | **PASS** |
+| VS Code Insiders (terminal) | 1.x | Windows | ✅ | ✅ | ❌ | ✅ | ✅ | **FAIL** |
+| GitHub Copilot (terminal) | — | Windows | ❌ | ❌ | ❌ | ❌ | ❌ | **FAIL** |
+| iTerm2 | 3.5+ | macOS | | | | | | _untested_ |
+| Terminal.app | — | macOS | | | | | | _untested_ |
+| GNOME Terminal | 3.x | Linux | | | | | | _untested_ |
+| Alacritty | 0.13+ | cross | | | | | | _untested_ |
+| Kitty | 0.35+ | cross | | | | | | _untested_ |
+| WezTerm | — | cross | | | | | | _untested_ |
+
+> **To contributors**: please fill in your terminal's results and submit a PR or comment.
+
+## Affected Unicode Ranges
+
+- **Emoji** (U+1F600–U+1F64F, U+1F900–U+1F9FF, etc.)
+- **CJK Unified Ideographs** (U+4E00–U+9FFF)
+- **CJK Compatibility Ideographs** (U+F900–U+FAFF)
+- **Fullwidth Forms** (U+FF01–U+FF60)
+- Any codepoint with Unicode `East_Asian_Width` = `W` (Wide) or `F` (Fullwidth)
+
+## Impact
+
+This bug breaks any TUI application that renders wide characters in a grid or alongside narrow characters. Affected applications include:
+- [Terminal.Gui](https://github.com/gui-cs/Terminal.Gui) (cross-platform .NET TUI toolkit)
+- Any ncurses/curses-based app using CJK or emoji
+- tmux, vim, etc. when displaying wide characters
+
+## Relevant Standards
+
+- [Unicode TR#11 – East Asian Width](https://www.unicode.org/reports/tr11/)
+- [POSIX `wcwidth(3)`](https://pubs.opengroup.org/onlinepubs/9699919799/functions/wcwidth.html)
+- [Unicode TR#51 – Emoji Presentation](https://www.unicode.org/reports/tr51/)
+
+## Environment
+
+- OS: [e.g., Windows 11 24H2]
+- Terminal: [e.g., VS Code Insiders 1.x integrated terminal]
+- Shell: [e.g., PowerShell 7.5]
+- Font: [e.g., Cascadia Code NF]
+- Locale: [e.g., en-US, UTF-8]
+
+## Screenshots
+
+<!-- Attach screenshots of correct (Windows Terminal) vs. broken (your terminal) output -->
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+// WideCharRepro - Minimal reproduction of wide/fullwidth character rendering issues.
+//
+// PURPOSE:
+// Many terminal emulators incorrectly handle "wide" (fullwidth) Unicode codepoints
+// (those with East Asian Width = Wide/Fullwidth, or emoji presentation). These
+// characters occupy 2 terminal columns, but some terminals only advance the cursor
+// by 1 column, causing subsequent text to overlap and the display to "tear."
+//
+// EXPECTED BEHAVIOR (correct terminals like Windows Terminal):
+//   - Each wide character occupies exactly 2 columns.
+//   - The grid lines up perfectly with no overlapping or shifted text.
+//   - The separator '|' characters in each row are vertically aligned.
+//
+// BROKEN BEHAVIOR (terminals with the bug):
+//   - Wide characters only advance the cursor 1 column instead of 2.
+//   - Grid columns misalign; text overlaps or shifts left.
+//   - Vertical '|' separators are NOT aligned across rows.
+//
+// HOW TO USE:
+//   dotnet run
+//   Compare output against a known-good terminal (e.g., Windows Terminal).
+//
+// DIAGNOSIS:
+//   If the '|' separators are not vertically aligned, the terminal is not
+//   correctly handling wide character cursor advancement.
+
+using System.Globalization;
+using System.Text;
+
+Console.OutputEncoding = Encoding.UTF8;
+
+// Ensure we're in a mode that supports Unicode output
+if (Environment.OSVersion.Platform == PlatformID.Win32NT)
+{
+    // Enable virtual terminal processing on Windows
+    Console.Write ("\x1b[?25l"); // Hide cursor for cleaner output
+}
+
+Console.WriteLine ("═══════════════════════════════════════════════════════════════════");
+Console.WriteLine ("  Wide Character Rendering Test");
+Console.WriteLine ("  If '|' separators are NOT vertically aligned, the terminal has");
+Console.WriteLine ("  a wide-character cursor advancement bug.");
+Console.WriteLine ("═══════════════════════════════════════════════════════════════════");
+Console.WriteLine ();
+
+// --- Test 1: Emoji (U+1F600 - U+1F64F) ---
+Console.WriteLine ("TEST 1: Emoji (each should occupy 2 columns)");
+Console.WriteLine ("┌──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┐");
+
+int startCodepoint = 0x1F600;
+for (int row = 0; row < 4; row++)
+{
+    Console.Write ("│");
+    for (int col = 0; col < 16; col++)
+    {
+        int cp = startCodepoint + (row * 16) + col;
+        string ch = char.ConvertFromUtf32 (cp);
+        Console.Write (ch);
+        Console.Write ("│");
+    }
+
+    Console.WriteLine ();
+}
+
+Console.WriteLine ("└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘");
+Console.WriteLine ();
+
+// --- Test 2: CJK Ideographs (U+4E00+) ---
+Console.WriteLine ("TEST 2: CJK Ideographs (each should occupy 2 columns)");
+Console.WriteLine ("┌──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┐");
+
+startCodepoint = 0x4E00;
+for (int row = 0; row < 4; row++)
+{
+    Console.Write ("│");
+    for (int col = 0; col < 16; col++)
+    {
+        int cp = startCodepoint + (row * 16) + col;
+        string ch = char.ConvertFromUtf32 (cp);
+        Console.Write (ch);
+        Console.Write ("│");
+    }
+
+    Console.WriteLine ();
+}
+
+Console.WriteLine ("└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘");
+Console.WriteLine ();
+
+// --- Test 3: Mixed narrow + wide on same line ---
+// Each line below is EXACTLY 20 display columns between the │ delimiters.
+Console.WriteLine ("TEST 3: Mixed content alignment");
+Console.WriteLine ("All lines are exactly 20 display columns. The '│' must align:");
+Console.WriteLine ("┌────────────────────┐");
+Console.WriteLine ("│ABCDEFGHIJKLMNOPQRST│ <- 20 narrow (20×1=20)");
+Console.WriteLine ("│😀😁😂😃😄😅😆😇😈😉│ <- 10 emoji  (10×2=20)");
+Console.WriteLine ("│你好世界测试宽字符验│ <- 10 CJK    (10×2=20)");
+Console.WriteLine ("│AB😀CD😁EF😂GH😃IJ😄│ <- mixed   (10×1 + 5×2=20)");
+Console.WriteLine ("└────────────────────┘");
+Console.WriteLine ();
+
+// --- Test 4: ANSI cursor positioning with wide chars ---
+Console.WriteLine ("TEST 4: Programmatic cursor-positioned grid");
+Console.WriteLine ("  Writing wide chars at absolute positions via ANSI escapes.");
+Console.WriteLine ("  If the terminal handles wcwidth correctly, all rows align.");
+Console.WriteLine ();
+
+// Get current cursor row (approximate - just write sequentially with known widths)
+string [] testRows =
+[
+    "│😀│😁│😂│🤣│😄│😅│😆│😇│",
+    "│──│──│──│──│──│──│──│──│",
+    "│🐶│🐱│🐭│🐹│🐰│🦊│🐻│🐼│",
+    "│──│──│──│──│──│──│──│──│",
+    "│你│好│世│界│测│试│宽│字│",
+    "│──│──│──│──│──│──│──│──│",
+];
+
+Console.WriteLine ("┌──┬──┬──┬──┬──┬──┬──┬──┐");
+
+foreach (string line in testRows)
+{
+    Console.WriteLine (line);
+}
+
+Console.WriteLine ("└──┴──┴──┴──┴──┴──┴──┴──┘");
+Console.WriteLine ();
+
+// --- Test 5: Explicit column-counting verification ---
+Console.WriteLine ("TEST 5: Column-width verification");
+Console.WriteLine ("  The 'X' markers below should align with column 20:");
+Console.WriteLine ();
+Console.WriteLine ("01234567890123456789X  <- 20 narrow (20×1=20)");
+Console.WriteLine ("😀😁😂😃😄😅😆😇😈😉X  <- 10 emoji  (10×2=20)");
+Console.WriteLine ("你好世界测试宽字符验X  <- 10 CJK    (10×2=20)");
+Console.WriteLine ("aあbいcうdえeおfかきX  <- mixed     (6×1 + 7×2=20)");
+Console.WriteLine ();
+Console.WriteLine ("If the 'X' markers don't vertically align at column 20,");
+Console.WriteLine ("the terminal is miscounting wide character widths.");
+Console.WriteLine ();
+
+// --- Summary ---
+Console.WriteLine ("═══════════════════════════════════════════════════════════════════");
+Console.WriteLine ("  DIAGNOSIS:");
+Console.WriteLine ("  • If all grids have aligned '│' separators → terminal is CORRECT");
+Console.WriteLine ("  • If grids are torn/misaligned → terminal has wcwidth bug");
+Console.WriteLine ("  • Common cause: terminal treats wide chars as 1 column, not 2");
+Console.WriteLine ("═══════════════════════════════════════════════════════════════════");
+
+// Show cursor again
+if (Environment.OSVersion.Platform == PlatformID.Win32NT)
+{
+    Console.Write ("\x1b[?25h");
+}
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+# Wide Character Rendering Reproduction
+
+A minimal reproduction app demonstrating incorrect wide/fullwidth Unicode character rendering in terminal emulators.
+
+## The Problem
+
+Terminal emulators must advance the cursor by **2 columns** for "wide" Unicode characters (East Asian Width = Wide/Fullwidth, emoji with presentation selectors). Some terminals incorrectly advance by only 1 column, causing:
+
+- Grid misalignment / display "tearing"
+- Overlapping text
+- Broken TUI (text user interface) applications
+
+## Screenshots
+
+### Correct rendering (Windows Terminal)
+
+All grid separators (`│`) are vertically aligned. Each wide character occupies exactly 2 terminal columns.
+
+![Correct rendering](correct.png)
+
+### Broken rendering (affected terminals)
+
+Grid separators are misaligned. Wide characters only advance the cursor by 1 column, causing all subsequent content on the line to shift left.
+
+![Broken rendering](broken.png)
+
+## Running the Reproduction
+
+```bash
+dotnet run
+```
+
+**Requirements:** .NET 10 SDK (or change `TargetFramework` in `.csproj` to your installed version, e.g., `net8.0` or `net9.0`).
+
+## What to Look For
+
+1. **Test 1–2 (Emoji / CJK grids):** The `│` separators should form perfectly vertical columns.
+2. **Test 3 (Mixed content):** Lines with mixed narrow + wide characters should fit within the box.
+3. **Test 4 (Programmatic grid):** Another grid alignment test with diverse wide characters.
+4. **Test 5 (Column verification):** The `X` markers should all appear at column 20.
+
+If any of these are misaligned, the terminal has a wide-character width calculation bug.
+
+## Technical Details
+
+Wide characters affected:
+- **Emoji** (U+1F600–U+1F64F, U+1F900–U+1F9FF, etc.)
+- **CJK Unified Ideographs** (U+4E00–U+9FFF)
+- **CJK Compatibility Ideographs** (U+F900–U+FAFF)
+- **Fullwidth Forms** (U+FF01–U+FF60)
+- Any character with `East_Asian_Width` property = `W` (Wide) or `F` (Fullwidth)
+
+The terminal must use the Unicode `East_Asian_Width` property (or an equivalent wcwidth implementation) to determine cursor advancement after printing each character.
+
+## Related Standards
+
+- [Unicode TR#11 – East Asian Width](https://www.unicode.org/reports/tr11/)
+- [POSIX `wcwidth(3)`](https://pubs.opengroup.org/onlinepubs/9699919799/functions/wcwidth.html)
+- [Unicode Emoji Presentation](https://www.unicode.org/reports/tr51/)
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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+</Project>