Prefer FMT_COMPILE for string formatting in VtRenderer

src/inc/til/format.h

@@ -0,0 +1,54 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+#pragma once
+
+#include <stdint.h>
+#include <string>
+
+#ifdef UNIT_TESTING
+#endif
+
+namespace til // Terminal Implementation Library. Also: "Today I Learned"
+{
+    namespace format
+    {
+        inline char* format_uint8(char* ptr, uint8_t number)
+        {
+            if (number >= 100)
+            {
+                *ptr++ = static_cast<char>((number / 100) + '0');
+            }
+            if (number >= 10)
+            {
+                *ptr++ = static_cast<char>(((number / 10) % 10) + '0');
+            }
+
+            *ptr++ = static_cast<char>((number % 10) + '0');
+            return ptr;
+        }
+
+        inline char* format(char* pDst, const char* pFormat, ...)
+        {
+            va_list args;
+            va_start(args, pFormat);
+
+            const char* pSrc = pFormat;
+            while (*pSrc != '\0')
+            {
+                if (*pSrc == '{' && *(pSrc + 1) == '}')
+                {
+                    pDst = format_uint8(pDst, va_arg(args, uint8_t));
+                    pSrc += 2;
+                    continue;
+                }
+
+                *pDst++ = *pSrc++;
+            }
+
+            va_end(args);
+
+            return pDst;
+        }
+    }
+}

src/renderer/vt/VtSequences.cpp

@@ -4,6 +4,7 @@
 #include "precomp.h"
 #include "vtrenderer.hpp"
 #include "../../inc/conattrs.hpp"
+#include "til/format.h"
 
 #pragma hdrstop
 using namespace Microsoft::Console::Render;
@@ -234,7 +235,10 @@ using namespace Microsoft::Console::Render;
                         (WI_IsFlagSet(wAttr, FOREGROUND_GREEN) ? 2 : 0) +
                         (WI_IsFlagSet(wAttr, FOREGROUND_BLUE) ? 4 : 0);
 
-    return _WriteFormattedString(&fmt, vtIndex);
+    char buf[6];
+    char* end = til::format::format(buf, "\x1b[{}m", vtIndex);
+    // An example string with max length would be "\x1b[100m", which has length = 6.
+    return _Write({ buf, static_cast<std::string_view::size_type>(end - buf) });
 }
 
 // Method Description:
@@ -248,11 +252,10 @@ using namespace Microsoft::Console::Render;
 [[nodiscard]] HRESULT VtEngine::_SetGraphicsRendition256Color(const WORD index,
                                                               const bool fIsForeground) noexcept
 {
-    const std::string fmt = fIsForeground ?
-                                "\x1b[38;5;%dm" :
-                                "\x1b[48;5;%dm";
-
-    return _WriteFormattedString(&fmt, ::Xterm256ToWindowsIndex(index));
+    char buf[11];
+    // An example string with max length would be "\x1b[38;5;128m", which has length = 11.
+    char* end = til::format::format(buf, "\x1b[{};5;{}m", fIsForeground ? 38 : 48, ::Xterm256ToWindowsIndex(index));
+    return _Write({buf, static_cast<std::string_view::size_type>(end - buf)});
 }
 
 // Method Description:
@@ -266,15 +269,15 @@ using namespace Microsoft::Console::Render;
 [[nodiscard]] HRESULT VtEngine::_SetGraphicsRenditionRGBColor(const COLORREF color,
                                                               const bool fIsForeground) noexcept
 {
-    const std::string fmt = fIsForeground ?
-                                "\x1b[38;2;%d;%d;%dm" :
-                                "\x1b[48;2;%d;%d;%dm";
-
     DWORD const r = GetRValue(color);
     DWORD const g = GetGValue(color);
     DWORD const b = GetBValue(color);
 
-    return _WriteFormattedString(&fmt, r, g, b);
+    char buf[19];
+    char* end = til::format::format(buf, "\x1b[{};2;{};{};{}m", fIsForeground ? 38 : 48, r, g, b);
+
+    // An example string with max length would be "\x1b[38;2;128;128;128m", which has length = 19.
+    return _Write({ buf, static_cast<std::string_view::size_type>(end - buf) });
 }
 
 // Method Description: