Use DPI from Print Preview on Windows, handle non square

printing/print_settings_initializer_win.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "printing/print_settings_initializer_win.h"
 
 #include <windows.h>
+#include <algorithm>
 
 #include "printing/print_settings.h"
 
 namespace printing {
 
 namespace {
 
 bool HasEscapeSupport(HDC hdc, DWORD escape) {
   const char* ptr = reinterpret_cast<const char*>(&escape);
   return ExtEscape(hdc, QUERYESCSUPPORT, sizeof(escape), ptr, 0, nullptr) > 0;
@@ skipping 79 matching lines @@
 // static
 void PrintSettingsInitializerWin::InitPrintSettings(
     HDC hdc,
     const DEVMODE& dev_mode,
     PrintSettings* print_settings) {
   DCHECK(hdc);
   DCHECK(print_settings);
 
   print_settings->SetOrientation(dev_mode.dmOrientation == DMORIENT_LANDSCAPE);
 
-  int dpi = GetDeviceCaps(hdc, LOGPIXELSX);
+  int dpi =
+      std::min(GetDeviceCaps(hdc, LOGPIXELSX), GetDeviceCaps(hdc, LOGPIXELSY));
   print_settings->set_dpi(dpi);
 
   const int kAlphaCaps = SB_CONST_ALPHA | SB_PIXEL_ALPHA;
   print_settings->set_supports_alpha_blend(
     (GetDeviceCaps(hdc, SHADEBLENDCAPS) & kAlphaCaps) == kAlphaCaps);
 
   // No printer device is known to advertise different dpi in X and Y axis; even

[Lei Zhang, 2017/03/31 22:21:13]

Don't we have a printer that refutes this statement? Can we update the comment
to explain our new strategy?

[rbpotter, 2017/04/01 00:08:02]

Done

   // the fax device using the 200x100 dpi setting. It's ought to break so many
   // applications that it's not even needed to care about. Blink doesn't support
   // different dpi settings in X and Y axis.
-  DCHECK_EQ(dpi, GetDeviceCaps(hdc, LOGPIXELSY));
-
   DCHECK_EQ(GetDeviceCaps(hdc, SCALINGFACTORX), 0);
   DCHECK_EQ(GetDeviceCaps(hdc, SCALINGFACTORY), 0);
 
   // Initialize |page_setup_device_units_|.
-  gfx::Size physical_size_device_units(GetDeviceCaps(hdc, PHYSICALWIDTH),
-                                       GetDeviceCaps(hdc, PHYSICALHEIGHT));
-  gfx::Rect printable_area_device_units(GetDeviceCaps(hdc, PHYSICALOFFSETX),
-                                        GetDeviceCaps(hdc, PHYSICALOFFSETY),
-                                        GetDeviceCaps(hdc, HORZRES),
-                                        GetDeviceCaps(hdc, VERTRES));
+  // DPI ratio should be an integer.

[Lei Zhang, 2017/03/31 22:21:13]

As in, we don't expect a printer to have a DPI of 450x300.

[rbpotter, 2017/04/01 00:08:02]

Actually fixed this. I have not seen any non-integer examples, but
realized I probably shouldn't assume that is the case.

+  int scale_x = GetDeviceCaps(hdc, LOGPIXELSX) / dpi;
+  int scale_y = GetDeviceCaps(hdc, LOGPIXELSY) / dpi;
+  gfx::Size physical_size_device_units(
+      GetDeviceCaps(hdc, PHYSICALWIDTH) / scale_x,
+      GetDeviceCaps(hdc, PHYSICALHEIGHT) / scale_y);
+  gfx::Rect printable_area_device_units(
+      GetDeviceCaps(hdc, PHYSICALOFFSETX) / scale_x,
+      GetDeviceCaps(hdc, PHYSICALOFFSETY) / scale_y,
+      GetDeviceCaps(hdc, HORZRES) / scale_x,
+      GetDeviceCaps(hdc, VERTRES) / scale_y);
 
   // Sanity check the printable_area: we've seen crashes caused by a printable
   // area rect of 0, 0, 0, 0, so it seems some drivers don't set it.
   if (printable_area_device_units.IsEmpty() ||
       !gfx::Rect(physical_size_device_units).Contains(
           printable_area_device_units)) {
     printable_area_device_units = gfx::Rect(physical_size_device_units);
   }
   DCHECK_EQ(print_settings->device_units_per_inch(), dpi);
   print_settings->SetPrinterPrintableArea(physical_size_device_units,
                                           printable_area_device_units,
                                           false);
+
   // Check for postscript first so that we can change the mode with the
   // first command.
   int level;
   if (IsPrinterPostScript(hdc, &level)) {
     if (level == 2) {
       print_settings->set_printer_type(
           PrintSettings::PrinterType::TYPE_POSTSCRIPT_LEVEL2);
       return;
     }
     DCHECK_EQ(3, level);
     print_settings->set_printer_type(
         PrintSettings::PrinterType::TYPE_POSTSCRIPT_LEVEL3);
     return;
   }
   if (IsPrinterXPS(hdc)) {
     print_settings->set_printer_type(PrintSettings::PrinterType::TYPE_XPS);
     return;
   }
   print_settings->set_printer_type(PrintSettings::PrinterType::TYPE_NONE);
 }
 
 }  // namespace printing