Add draw_utils::AdjustBottomGapForRightSidePage().

Currently in PDFiumEngine::FillPageSides() the logic for handling the
bottom gaps of pages on the right side is in the FillPageSides().

This CL moves that logic to
draw_utils::AdjustBottomGapForRightSidePage(), making it testable.

Bug: 51472
Change-Id: I5c5d0929c46745ee315f3b7ce77dc4cb0b44e5f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726757Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Jeremy Chinsen <chinsenj@google.com>
Cr-Commit-Position: refs/heads/master@{#682888}

pdf/draw_utils/coordinates.cc

@@ -12,6 +12,11 @@
 namespace chrome_pdf {
 namespace draw_utils {
 
+void AdjustBottomGapForRightSidePage(int page_x, pp::Rect* bottom_gap) {
+  bottom_gap->set_x(page_x);
+  bottom_gap->set_width(bottom_gap->width() / 2);
+}
+
 void ExpandDocumentSize(const pp::Size& rect_size, pp::Size* doc_size) {
   int width_diff = std::max(0, rect_size.width() - doc_size->width());
   doc_size->Enlarge(width_diff, rect_size.height());

pdf/draw_utils/coordinates.h

@@ -26,6 +26,12 @@ struct PageInsetSizes {
   int bottom;
 };
 
+// Given a right page's |bottom_gap|, reduce it to only the part of |bottom_gap|
+// that is directly below the right page by translating |bottom_gap| to |page_x|
+// and halving its width. This avoids over-drawing empty space on the already
+// drawn left page and the empty space to the right of the page.
+void AdjustBottomGapForRightSidePage(int page_x, pp::Rect* bottom_gap);
+
 // Given |rect_size|, sets the width of |doc_size| to the max of |rect_size|'s
 // width and |doc_size|'s width. Also adds the height of |rect_size| to
 // |doc_size|'s height.

pdf/draw_utils/coordinates_unittest.cc

@@ -40,6 +40,20 @@ void CompareSize(const pp::Size& expected_size, const pp::Size& given_size) {
 
 }  // namespace
 
+TEST(CoordinateTest, AdjustBottomGapForRightSidePage) {
+  pp::Rect bottom_gap(0, 10, 500, 100);
+  AdjustBottomGapForRightSidePage(250, &bottom_gap);
+  CompareRect({250, 10, 250, 100}, bottom_gap);
+
+  bottom_gap.SetRect(15, 20, 700, 100);
+  AdjustBottomGapForRightSidePage(365, &bottom_gap);
+  CompareRect({365, 20, 350, 100}, bottom_gap);
+
+  bottom_gap.SetRect(100, 40, 951, 200);
+  AdjustBottomGapForRightSidePage(450, &bottom_gap);
+  CompareRect({450, 40, 475, 200}, bottom_gap);
+}
+
 TEST(CoordinateTest, ExpandDocumentSize) {
   pp::Size doc_size(100, 400);
 

pdf/pdfium/pdfium_engine.cc

@@ -2837,9 +2837,8 @@ void PDFiumEngine::FillPageSides(int progressive_index) {
         page_in_screen.bottom(), dirty_in_screen);
 
     if (page_index % 2 == 1) {
-      // Only draw over the right two-up view column with empty space.
-      bottom_in_screen.set_width(bottom_in_screen.width() / 2);
-      bottom_in_screen.set_x(page_in_screen.x());
+      draw_utils::AdjustBottomGapForRightSidePage(page_in_screen.x(),
+                                                  &bottom_in_screen);
     }
 
     bottom_in_screen = bottom_in_screen.Intersect(dirty_in_screen);