RenderText: Allow setting display offset explicitly

ui/gfx/render_text_unittest.cc

Index: ui/gfx/render_text_unittest.cc
diff --git a/ui/gfx/render_text_unittest.cc b/ui/gfx/render_text_unittest.cc
index 4686066f088953085ff1df8d5e7bb381efa47866..3cd3b98e75e0eea0e30a426aeb57a2aefdd21ce2 100644
--- a/ui/gfx/render_text_unittest.cc
+++ b/ui/gfx/render_text_unittest.cc
@@ -1040,7 +1040,7 @@ TEST_F(RenderTextTest, SelectAll) {
   EXPECT_EQ(was_rtl, base::i18n::IsRTL());
 }
 
-  TEST_F(RenderTextTest, MoveCursorLeftRightWithSelection) {
+TEST_F(RenderTextTest, MoveCursorLeftRightWithSelection) {
   scoped_ptr<RenderText> render_text(RenderText::CreateInstance());
   render_text->SetText(WideToUTF16(L"abc\x05d0\x05d1\x05d2"));
   // Left arrow on select ranging (6, 4).
@@ -1488,6 +1488,80 @@ TEST_F(RenderTextTest, GetTextOffsetHorizontalDefaultInRTL) {
   SetRTL(was_rtl);
 }
 
+TEST_F(RenderTextTest, SetDisplayOffset) {
+  scoped_ptr<RenderText> render_text(RenderText::CreateInstance());
+  render_text->SetText(ASCIIToUTF16("abcdefg"));
+  render_text->SetFontList(FontList("Arial, 13px"));
+
+  const Size font_size(render_text->GetContentWidth(),
+                       render_text->font_list().GetHeight());
+  const int kEnlargement = 10;
+
+  // Set display width |kEnlargement| pixels greater than content width and test
+  // different possible situations. In this case the only possible display
+  // offset is zero.
+  Rect display_rect(font_size);
+  display_rect.Inset(0, 0, -kEnlargement, 0);
+  render_text->SetDisplayRect(display_rect);
+
+  struct {
+    HorizontalAlignment alignment;
+    int offset;
+  } small_content_cases[] = {
+    { ALIGN_LEFT, -kEnlargement },
+    { ALIGN_LEFT, 0 },
+    { ALIGN_LEFT, kEnlargement },
+    { ALIGN_RIGHT, -kEnlargement },
+    { ALIGN_RIGHT, 0 },
+    { ALIGN_RIGHT, kEnlargement },
+    { ALIGN_CENTER, -kEnlargement },
+    { ALIGN_CENTER, 0 },
+    { ALIGN_CENTER, kEnlargement },
+  };
+
+  for (size_t i = 0; i < ARRAYSIZE_UNSAFE(small_content_cases); i++) {
+    render_text->SetHorizontalAlignment(small_content_cases[i].alignment);
+    render_text->SetDisplayOffset(small_content_cases[i].offset);
+    EXPECT_EQ(0, render_text->GetUpdatedDisplayOffset().x());
+  }
+
+  // Set display width |kEnlargement| pixels less than content width and test
+  // different possible situations.
+  display_rect = Rect(font_size);
+  display_rect.Inset(0, 0, kEnlargement, 0);
+  render_text->SetDisplayRect(display_rect);
+
+  struct {
+    HorizontalAlignment alignment;
+    int offset;
+    int expected_offset;
+  } large_content_cases[] = {
+    // When text is left-aligned, display offset can be in range
+    // [-kEnlargement, 0].
+    { ALIGN_LEFT, -2 * kEnlargement, -kEnlargement },
+    { ALIGN_LEFT, -kEnlargement / 2, -kEnlargement / 2 },
+    { ALIGN_LEFT, kEnlargement, 0 },
+    // When text is right-aligned, display offset can be in range
+    // [0, kEnlargement].
+    { ALIGN_RIGHT, -kEnlargement, 0 },
+    { ALIGN_RIGHT, kEnlargement / 2, kEnlargement / 2 },
+    { ALIGN_RIGHT, 2 * kEnlargement, kEnlargement },
+    // When text is center-aligned, display offset can be in range
+    // [-kEnlargement / 2, kEnlargement / 2].
+    { ALIGN_CENTER, -kEnlargement, -kEnlargement / 2 },
+    { ALIGN_CENTER, -kEnlargement / 4, -kEnlargement / 4 },
+    { ALIGN_CENTER, kEnlargement / 4, kEnlargement / 4 },
+    { ALIGN_CENTER, kEnlargement, kEnlargement / 2 },
+  };
+
+  for (size_t i = 0; i < ARRAYSIZE_UNSAFE(large_content_cases); i++) {
+    render_text->SetHorizontalAlignment(large_content_cases[i].alignment);
+    render_text->SetDisplayOffset(large_content_cases[i].offset);
+    EXPECT_EQ(large_content_cases[i].expected_offset,
+              render_text->GetUpdatedDisplayOffset().x());
+  }
+}
+
 TEST_F(RenderTextTest, SameFontForParentheses) {
   struct {
     const base::char16 left_char;