Mac printing: Autorotate printed pages so their orientation is the same as the destination page.

printing/pdf_metafile_cg_mac.cc

Index: printing/pdf_metafile_cg_mac.cc
===================================================================
--- printing/pdf_metafile_cg_mac.cc	(revision 142466)
+++ printing/pdf_metafile_cg_mac.cc	(working copy)
@@ -4,6 +4,8 @@
 
 #include "printing/pdf_metafile_cg_mac.h"
 
+#include <algorithm>
+
 #include "base/file_path.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
@@ -175,7 +177,8 @@
                                bool shrink_to_fit,
                                bool stretch_to_fit,
                                bool center_horizontally,
-                               bool center_vertically) const {
+                               bool center_vertically,
+                               bool autorotate) const {
   CGPDFDocumentRef pdf_doc = GetPDFDocument();
   if (!pdf_doc) {
     LOG(ERROR) << "Unable to create PDF document from data";
@@ -184,38 +187,58 @@
   CGPDFPageRef pdf_page = CGPDFDocumentGetPage(pdf_doc, page_number);
   CGRect source_rect = CGPDFPageGetBoxRect(pdf_page, kCGPDFCropBox);
   float scaling_factor = 1.0;
+  const bool source_is_landscape =
+        (source_rect.size.width > source_rect.size.height);
+  const bool dest_is_landscape = (rect.size.width > rect.size.height);
+  const bool rotate =
+      autorotate ? (source_is_landscape != dest_is_landscape) : false;
+  const float source_width =
+      rotate ? source_rect.size.height : source_rect.size.width;
+  const float source_height =
+      rotate ? source_rect.size.width : source_rect.size.height;
+
   // See if we need to scale the output.
-  bool scaling_needed =
-      (shrink_to_fit && ((source_rect.size.width > rect.size.width) ||
-                         (source_rect.size.height > rect.size.height))) ||
-      (stretch_to_fit && (source_rect.size.width < rect.size.width) &&
-          (source_rect.size.height < rect.size.height));
+  const bool scaling_needed =
+      (shrink_to_fit && ((source_width > rect.size.width) ||
+                         (source_height > rect.size.height))) ||
+      (stretch_to_fit && (source_width < rect.size.width) &&
+                         (source_height < rect.size.height));
   if (scaling_needed) {
-    float x_scaling_factor = rect.size.width / source_rect.size.width;
-    float y_scaling_factor = rect.size.height / source_rect.size.height;
-    if (x_scaling_factor > y_scaling_factor) {
-      scaling_factor = y_scaling_factor;
-    } else {
-      scaling_factor = x_scaling_factor;
-    }
+    float x_scaling_factor = rect.size.width / source_width;
+    float y_scaling_factor = rect.size.height / source_height;
+    scaling_factor = std::min(x_scaling_factor, y_scaling_factor);
   }
-  // Some PDFs have a non-zero origin. Need to take that into account.
-  float x_offset = -1 * source_rect.origin.x * scaling_factor;
-  float y_offset = -1 * source_rect.origin.y * scaling_factor;
+  // Some PDFs have a non-zero origin. Need to take that into account and align
+  // the PDF to the origin.
+  const float x_origin_offset = -1 * source_rect.origin.x;
+  const float y_origin_offset = -1 * source_rect.origin.y;
 
-  if (center_horizontally) {
-    x_offset += (rect.size.width -
-                     (source_rect.size.width * scaling_factor))/2;
-  }
-  if (center_vertically) {
-    y_offset += (rect.size.height -
-                     (source_rect.size.height * scaling_factor))/2;
-  }
+  // If the PDF needs to be centered, calculate the offsets here.
+  float x_offset = center_horizontally ?
+      ((rect.size.width - (source_width * scaling_factor)) / 2) : 0;
+  if (rotate)
+    x_offset = -x_offset;
+
+  float y_offset = center_vertically ?
+      ((rect.size.height - (source_height * scaling_factor)) / 2) : 0;
+
   CGContextSaveGState(context);
+
+  // The transform operations specified here gets applied in reverse order.
+  // i.e. the origin offset translation happens first.
+  // Origin is at bottom-left.
   CGContextTranslateCTM(context, x_offset, y_offset);

[kmadhusu, 2012/06/16 00:44:11]

Why can't we do a single Translation operation like before?

[Lei Zhang, 2012/06/16 01:47:20]

We may be able to, but it's easier to visualize what is happening when you break
the translation into distinct steps:

- adjust for the offset
- adjust for the rotation
- adjust for centering

+  if (rotate) {
+    CGContextTranslateCTM(context, rect.size.width, 0);

[kmadhusu, 2012/06/16 00:44:11]

Can you add a comment on why we need to do this translation?

[Lei Zhang, 2012/06/16 01:47:20]

Done.

+    // Rotates counter-clockwise by 90 degrees.
+    CGContextRotateCTM(context, M_PI_2);
+  }
   CGContextScaleCTM(context, scaling_factor, scaling_factor);
+  CGContextTranslateCTM(context, x_origin_offset, y_origin_offset);
+
   CGContextDrawPDFPage(context, pdf_page);
   CGContextRestoreGState(context);
+
   return true;
 }
 
@@ -269,7 +292,7 @@
   DCHECK(pdf_data_.get());
   DCHECK(!context_.get());
 
-  std::string path_string = file_path.value();
+  const std::string& path_string = file_path.value();
   ScopedCFTypeRef<CFURLRef> path_url(CFURLCreateFromFileSystemRepresentation(
       kCFAllocatorDefault, reinterpret_cast<const UInt8*>(path_string.c_str()),
       path_string.length(), false));