Add GetPageInsetsForTwoUpView() to pdf/draw_utils.

In PDFiumEngine, currently the size of the shadows surrounding a
page is constant because there is only a single page view. With
the addition of two-up view, the sizes of the shadows will depend
on the position of the page within its document.

draw_utils::GetPageInsetsForTwoUpView() is a function that takes
the position of the page within the document and shadow sizes,
and returns the proper configuration of inset sizes for two-up
view. Having this as a separate function makes this logic testable
and reduces the future complexity of PDFiumEngine.

Bug: 51472
Change-Id: Icecbb05f672b10ca682ae383308abb96075b64ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1707951
Commit-Queue: Jeremy Chinsen <chinsenj@google.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#679590}

pdf/draw_utils/coordinates.cc

@@ -17,6 +17,25 @@ void ExpandDocumentSize(const pp::Size& rect_size, pp::Size* doc_size) {
   doc_size->Enlarge(width_diff, rect_size.height());
 }
 
+PageInsetSizes GetPageInsetsForTwoUpView(
+    size_t page_index,
+    size_t num_of_pages,
+    const PageInsetSizes& single_view_insets,
+    int horizontal_separator) {
+  DCHECK_GE(page_index, 0u);
+  DCHECK_LT(page_index, num_of_pages);
+
+  // Don't change |two_up_insets| if the page is on the left side and is the
+  // last page. In this case, the shadows on both sides should be the same size.
+  PageInsetSizes two_up_insets = single_view_insets;
+  if (page_index % 2 == 1)
+    two_up_insets.left = horizontal_separator;
+  else if (page_index != num_of_pages - 1)
+    two_up_insets.right = horizontal_separator;
+
+  return two_up_insets;
+}
+
 pp::Rect GetLeftFillRect(const pp::Rect& page_rect,
                          const PageInsetSizes& inset_sizes,
                          int bottom_separator) {

pdf/draw_utils/coordinates.h

@@ -5,6 +5,8 @@
 #ifndef PDF_DRAW_UTILS_COORDINATES_H_
 #define PDF_DRAW_UTILS_COORDINATES_H_
 
+#include "stddef.h"
+
 #include "ppapi/cpp/rect.h"
 
 namespace pp {
@@ -29,6 +31,15 @@ struct PageInsetSizes {
 // |doc_size|'s height.
 void ExpandDocumentSize(const pp::Size& rect_size, pp::Size* doc_size);
 
+// Given |page_index|, and |num_of_pages|, return the configuration of
+// |single_view_insets| and |horizontal_separator| for the current page in
+// two-up view.
+PageInsetSizes GetPageInsetsForTwoUpView(
+    size_t page_index,
+    size_t num_of_pages,
+    const PageInsetSizes& single_view_insets,
+    int horizontal_separator);
+
 // Given |page_rect| in document coordinates, |inset_sizes|, and
 // |bottom_separator|, return a pp::Rect object representing the gap on the
 // left side of the page created by insetting the page. I.e. the difference,

pdf/draw_utils/coordinates_unittest.cc

@@ -13,10 +13,19 @@ namespace draw_utils {
 namespace {
 
 constexpr int kBottomSeparator = 4;
+constexpr int kHorizontalSeparator = 1;
 constexpr PageInsetSizes kLeftInsets{5, 3, 1, 7};
 constexpr PageInsetSizes kRightInsets{1, 3, 5, 7};
 constexpr PageInsetSizes kSingleViewInsets{5, 3, 5, 7};
 
+void CompareInsetSizes(const PageInsetSizes& expected_insets,
+                       const PageInsetSizes& given_insets) {
+  EXPECT_EQ(expected_insets.left, given_insets.left);
+  EXPECT_EQ(expected_insets.top, given_insets.top);
+  EXPECT_EQ(expected_insets.right, given_insets.right);
+  EXPECT_EQ(expected_insets.bottom, given_insets.bottom);
+}
+
 }  // namespace
 
 TEST(CoordinateTest, ExpandDocumentSize) {
@@ -44,6 +53,28 @@ TEST(CoordinateTest, ExpandDocumentSize) {
   EXPECT_EQ(1450, doc_size.height());
 }
 
+TEST(CoordinateTest, GetPageInsetsForTwoUpView) {
+  // Page is on the left side and isn't the last page in the document.
+  CompareInsetSizes(kLeftInsets,
+                    GetPageInsetsForTwoUpView(0, 10, kSingleViewInsets,
+                                              kHorizontalSeparator));
+
+  // Page is on the left side and is the last page in the document.
+  CompareInsetSizes(kSingleViewInsets,
+                    GetPageInsetsForTwoUpView(10, 11, kSingleViewInsets,
+                                              kHorizontalSeparator));
+
+  // Only one page in the document.
+  CompareInsetSizes(
+      kSingleViewInsets,
+      GetPageInsetsForTwoUpView(0, 1, kSingleViewInsets, kHorizontalSeparator));
+
+  // Page is on the right side of the document.
+  CompareInsetSizes(
+      kRightInsets,
+      GetPageInsetsForTwoUpView(1, 4, kSingleViewInsets, kHorizontalSeparator));
+}
+
 TEST(CoordinateTest, GetLeftFillRect) {
   // Testing various rectangles with different positions and sizes.
   pp::Rect page_rect(10, 20, 400, 500);