Add draw_utils::CenterRectHorizontally().

In single-view, pages are horizontally centered within the document.
This centering is being done in PDFiumEngine, making it difficult to
test.

This CL moves the centering logic for single-view to
draw_utils::CenterRectHorizontally(). This allows us to test the logic.

Bug: 51472
Change-Id: Idd67cde3c57d4155c9e02ca82a36ad19a6205f08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1730524
Commit-Queue: Jeremy Chinsen <chinsenj@google.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683387}

pdf/draw_utils/coordinates.cc

@@ -17,6 +17,12 @@ void AdjustBottomGapForRightSidePage(int page_x, pp::Rect* bottom_gap) {
   bottom_gap->set_width(bottom_gap->width() / 2);
 }
 
+void CenterRectHorizontally(int doc_width, pp::Rect* rect) {
+  DCHECK_GE(doc_width, rect->width());
+
+  rect->set_x((doc_width - rect->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

@@ -32,6 +32,10 @@ struct PageInsetSizes {
 // drawn left page and the empty space to the right of the page.
 void AdjustBottomGapForRightSidePage(int page_x, pp::Rect* bottom_gap);
 
+// Given |doc_width|, horizontally center |rect| within the document.
+// |doc_width| must be greater than or equal to |rect|.
+void CenterRectHorizontally(int doc_width, pp::Rect* rect);
+
 // 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

@@ -54,6 +54,20 @@ TEST(CoordinateTest, AdjustBottomGapForRightSidePage) {
   CompareRect({450, 40, 475, 200}, bottom_gap);
 }
 
+TEST(CoordinateTest, CenterRectHorizontally) {
+  pp::Rect page_rect(10, 20, 400, 300);
+  CenterRectHorizontally(600, &page_rect);
+  CompareRect({100, 20, 400, 300}, page_rect);
+
+  page_rect.SetRect(300, 450, 500, 700);
+  CenterRectHorizontally(800, &page_rect);
+  CompareRect({150, 450, 500, 700}, page_rect);
+
+  page_rect.SetRect(800, 100, 200, 250);
+  CenterRectHorizontally(350, &page_rect);
+  CompareRect({75, 100, 200, 250}, page_rect);
+}
+
 TEST(CoordinateTest, ExpandDocumentSize) {
   pp::Size doc_size(100, 400);
 

pdf/pdfium/pdfium_engine.cc

@@ -2395,8 +2395,7 @@ void PDFiumEngine::AppendPageRectToPages(const pp::Rect& page_rect,
 void PDFiumEngine::LoadPagesInSingleView(std::vector<pp::Rect> page_rects,
                                          bool reload) {
   for (size_t i = 0; i < page_rects.size(); ++i) {
-    // Center pages relative to the entire document.
-    page_rects[i].set_x((layout_.size().width() - page_rects[i].width()) / 2);
+    draw_utils::CenterRectHorizontally(layout_.size().width(), &page_rects[i]);
     InsetPage(i, page_rects.size(), /*multiplier=*/1, &page_rects[i]);
     AppendPageRectToPages(page_rects[i], i, reload);
   }