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/fxge/include/fx_ge.h"
 
 #if _FX_OS_ == _FX_WIN32_DESKTOP_ || _FX_OS_ == _FX_WIN64_DESKTOP_
 
@@ skipping 264 matching lines @@
 
   // 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);

[hal.canary, 2016/07/29 15:26:21]

why is this true?

[Lei Zhang, 2016/07/29 15:55:52]

It's held up so far with my test cases. Do you have an example that breaks this
assertion? If so, I can work with that and fix this more.

+
+    // Round the spacing to the nearest integer, but keep track of the rounding
+    // error for calculating the next spacing value.
+    FX_FLOAT fPixelSpacing = charpos.m_OriginX - fPreviousOriginX;
+    spacing[i] = FXSYS_round(fPixelSpacing);

[Lei Zhang, 2016/07/29 22:42:08]

I printed a random page from Wikipedia and there are places where the rounding
causes bad kerning. I guess I'll have to try MM_TWIPS or something other map
mode to get more accurate spacing.

+    fPreviousOriginX = charpos.m_OriginX - (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_