Fix CGdiPrinterDriver::DrawDeviceText() to draw multiple characters.

core/fxge/win32/fx_win32_print.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "core/fxcrt/include/fx_system.h"
 
 #if _FX_OS_ == _FX_WIN32_DESKTOP_ || _FX_OS_ == _FX_WIN64_DESKTOP_
 
@@ skipping 191 matching lines @@
                                           const CFX_Matrix* pObject2Device,
                                           FX_FLOAT font_size,
                                           uint32_t color) {
 #if defined(PDFIUM_PRINT_TEXT_WITH_GDI)
   if (!g_pdfium_print_text_with_gdi)
     return FALSE;
 
   if (nChars < 1 || !pFont || !pFont->IsEmbedded() || !pFont->IsTTFont())
     return FALSE;
 
+  // Scale factor used to minimize the kerning problems caused by rounding
+  // errors below. Value choosen based on the title of https://crbug.com/18383
+  const double kScaleFactor = 10;
+
   // Font
   //
   // Note that |pFont| has the actual font to render with embedded within, but
   // but unfortunately AddFontMemResourceEx() does not seem to cooperate.
   // Loading font data to memory seems to work, but then enumerating the fonts
   // fails to find it. This requires more investigation. In the meanwhile,
   // assume the printing is happening on the machine that generated the PDF, so
   // the embedded font, if not a web font, is available through GDI anyway.
   // TODO(thestig): Figure out why AddFontMemResourceEx() does not work.
   // Generalize this method to work for all PDFs with embedded fonts.
   // In sandboxed environments, font loading may not work at all, so this may be
   // the best possible effort.
   LOGFONT lf = {};
-  lf.lfHeight = -font_size;
+  lf.lfHeight = -font_size * kScaleFactor;
   lf.lfWeight = pFont->IsBold() ? FW_BOLD : FW_NORMAL;
   lf.lfItalic = pFont->IsItalic();
   lf.lfCharSet = DEFAULT_CHARSET;
 
   const CFX_WideString wsName = pFont->GetFaceName().UTF8Decode();
   int iNameLen = std::min(wsName.GetLength(), LF_FACESIZE - 1);
   memcpy(lf.lfFaceName, wsName.c_str(), sizeof(lf.lfFaceName[0]) * iNameLen);
   lf.lfFaceName[iNameLen] = 0;
 
   HFONT hFont = CreateFontIndirect(&lf);
@@ skipping 23 matching lines @@
   // If the selected font is not the requested font, then bail out. This can
   // happen with web fonts, for example.
   wchar_t* wsSelectedName = reinterpret_cast<wchar_t*>(
       buf.data() + reinterpret_cast<size_t>(pTextMetric->otmpFaceName));
   if (wsName != wsSelectedName)
     return FALSE;
 
   // Transforms
   SetGraphicsMode(m_hDC, GM_ADVANCED);
   XFORM xform;
-  xform.eM11 = pObject2Device->GetA();
-  xform.eM12 = pObject2Device->GetB();
-  xform.eM21 = -pObject2Device->GetC();
-  xform.eM22 = -pObject2Device->GetD();
+  xform.eM11 = pObject2Device->GetA() / kScaleFactor;
+  xform.eM12 = pObject2Device->GetB() / kScaleFactor;
+  xform.eM21 = -pObject2Device->GetC() / kScaleFactor;
+  xform.eM22 = -pObject2Device->GetD() / kScaleFactor;
   xform.eDx = pObject2Device->GetE();
   xform.eDy = pObject2Device->GetF();
   ModifyWorldTransform(m_hDC, &xform, MWT_LEFTMULTIPLY);
 
   // Color
   int iUnusedAlpha;
   FX_COLORREF rgb;
   ArgbDecode(color, iUnusedAlpha, rgb);
   SetTextColor(m_hDC, rgb);
   SetBkMode(m_hDC, TRANSPARENT);
 
   // Text
   CFX_WideString wsText;
+  std::vector<INT> spacing(nChars);
+  FX_FLOAT fPreviousOriginX = 0;
   for (int i = 0; i < nChars; ++i) {
     // Only works with PDFs from Skia's PDF generator. Cannot handle arbitrary
     // values from PDFs.
     const FXTEXT_CHARPOS& charpos = pCharPos[i];
-    ASSERT(charpos.m_OriginX == 0);
-    ASSERT(charpos.m_OriginY == 0);
     ASSERT(charpos.m_AdjustMatrix[0] == 0);
     ASSERT(charpos.m_AdjustMatrix[1] == 0);
     ASSERT(charpos.m_AdjustMatrix[2] == 0);
     ASSERT(charpos.m_AdjustMatrix[3] == 0);
+    ASSERT(charpos.m_OriginY == 0);
+
+    // Round the spacing to the nearest integer, but keep track of the rounding
+    // error for calculating the next spacing value.
+    FX_FLOAT fOriginX = charpos.m_OriginX * kScaleFactor;
+    FX_FLOAT fPixelSpacing = fOriginX - fPreviousOriginX;
+    spacing[i] = FXSYS_round(fPixelSpacing);
+    fPreviousOriginX = fOriginX - (fPixelSpacing - spacing[i]);
+
     wsText += charpos.m_GlyphIndex;
   }
 
   // Draw
   SetTextAlign(m_hDC, TA_LEFT | TA_BASELINE);
   if (ExtTextOutW(m_hDC, 0, 0, ETO_GLYPH_INDEX, nullptr, wsText.c_str(), nChars,
-                  nullptr)) {
+                  nChars > 1 ? &spacing[1] : nullptr)) {
     return TRUE;
   }
 
   // Give up and fail if there is no way to get the font to try again.
   if (!g_pdfium_typeface_accessible_func)
     return FALSE;
 
   // Try to get the font and draw again.
   g_pdfium_typeface_accessible_func(&lf, wsText.c_str(), nChars);
   return ExtTextOutW(m_hDC, 0, 0, ETO_GLYPH_INDEX, nullptr, wsText.c_str(),
-                     nChars, nullptr);
+                     nChars, nChars > 1 ? &spacing[1] : nullptr);
 #else
   return FALSE;
 #endif
 }
 
 #endif  // _FX_OS_ == _FX_WIN32_DESKTOP_ || _FX_OS_ == _FX_WIN64_DESKTOP_