Enable subpixel positioning for chrome os for fractional dsf

This patch enables the font subpixel positioning for the browser ui
and blink for fractional device scale factors.

It also adds a switch to force disable subpixel positioning for
easier debugging and testing on devices.

Bug: 839214
Change-Id: If8fd7dbc39ac3950bc27b5b7435b482fb4931065
Component: Font, subpixel positioning, kerning
Reviewed-on: https://chromium-review.googlesource.com/1053289Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558764}

ash/display/display_manager_unittest.cc

@@ -3376,8 +3376,97 @@ class FontTestHelper : public AshTestBase {
   DISALLOW_COPY_AND_ASSIGN(FontTestHelper);
 };
 
+bool IsTextSubpixelPositioningEnabled() {
+  gfx::FontRenderParams params =
+      gfx::GetFontRenderParams(gfx::FontRenderParamsQuery(), nullptr);
+  return params.subpixel_positioning;
+}
+
+gfx::FontRenderParams::Hinting GetFontHintingParams() {
+  gfx::FontRenderParams params =
+      gfx::GetFontRenderParams(gfx::FontRenderParamsQuery(), nullptr);
+  return params.hinting;
+}
+
 }  // namespace
 
+using DisplayManagerFontTest = testing::Test;
+
+TEST_F(DisplayManagerFontTest, TextSubpixelPositioningWithDsf100Internal) {
+  FontTestHelper helper(1.0f, FontTestHelper::INTERNAL);
+  ASSERT_DOUBLE_EQ(
+      1.0f,
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
+  EXPECT_FALSE(IsTextSubpixelPositioningEnabled());
+  EXPECT_NE(gfx::FontRenderParams::HINTING_NONE, GetFontHintingParams());
+}
+
+TEST_F(DisplayManagerFontTest, TextSubpixelPositioningWithDsf200Internal) {
+  FontTestHelper helper(2.0f, FontTestHelper::INTERNAL);
+  ASSERT_DOUBLE_EQ(
+      2.0f,
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
+  EXPECT_FALSE(IsTextSubpixelPositioningEnabled());
+  EXPECT_NE(gfx::FontRenderParams::HINTING_NONE, GetFontHintingParams());
+
+  display::test::DisplayManagerTestApi(helper.display_manager())
+      .SetDisplayUIScale(display::Screen::GetScreen()->GetPrimaryDisplay().id(),
+                         2.0f);
+
+  ASSERT_DOUBLE_EQ(
+      1.0f,
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
+  EXPECT_FALSE(IsTextSubpixelPositioningEnabled());
+  EXPECT_NE(gfx::FontRenderParams::HINTING_NONE, GetFontHintingParams());
+}
+
+TEST_F(DisplayManagerFontTest, TextSubpixelPositioningWithDsf100External) {
+  FontTestHelper helper(1.0f, FontTestHelper::EXTERNAL);
+  ASSERT_DOUBLE_EQ(
+      1.0f,
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
+  EXPECT_FALSE(IsTextSubpixelPositioningEnabled());
+  EXPECT_NE(gfx::FontRenderParams::HINTING_NONE, GetFontHintingParams());
+}
+
+TEST_F(DisplayManagerFontTest, TextSubpixelPositioningWithDsf125External) {
+  FontTestHelper helper(1.25f, FontTestHelper::EXTERNAL);
+  ASSERT_DOUBLE_EQ(
+      1.25f,
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
+  EXPECT_TRUE(IsTextSubpixelPositioningEnabled());
+  EXPECT_EQ(gfx::FontRenderParams::HINTING_NONE, GetFontHintingParams());
+}
+
+TEST_F(DisplayManagerFontTest, TextSubpixelPositioningWithDsf200External) {
+  FontTestHelper helper(2.0f, FontTestHelper::EXTERNAL);
+  ASSERT_DOUBLE_EQ(
+      2.0f,
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
+  EXPECT_FALSE(IsTextSubpixelPositioningEnabled());
+  EXPECT_NE(gfx::FontRenderParams::HINTING_NONE, GetFontHintingParams());
+}
+
+TEST_F(DisplayManagerFontTest,
+       TextSubpixelPositioningWithDsf125InternalWithScaling) {
+  FontTestHelper helper(1.25f, FontTestHelper::INTERNAL);
+  ASSERT_DOUBLE_EQ(
+      1.0f,
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
+  EXPECT_FALSE(IsTextSubpixelPositioningEnabled());
+  EXPECT_NE(gfx::FontRenderParams::HINTING_NONE, GetFontHintingParams());
+
+  display::test::DisplayManagerTestApi(helper.display_manager())
+      .SetDisplayUIScale(display::Screen::GetScreen()->GetPrimaryDisplay().id(),
+                         0.8f);
+
+  ASSERT_DOUBLE_EQ(
+      1.25f,
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
+  EXPECT_TRUE(IsTextSubpixelPositioningEnabled());
+  EXPECT_EQ(gfx::FontRenderParams::HINTING_NONE, GetFontHintingParams());
+}
+
 TEST_F(DisplayManagerTest, CheckInitializationOfRotationProperty) {
   int64_t id = display_manager()->GetDisplayAt(0).id();
   display_manager()->RegisterDisplayProperty(

ui/gfx/font_render_params_linux.cc

@@ -278,11 +278,16 @@ FontRenderParams GetFontRenderParams(const FontRenderParamsQuery& query,
     params.hinting = FontRenderParams::HINTING_FULL;
     params.subpixel_rendering = FontRenderParams::SUBPIXEL_RENDERING_NONE;
     params.subpixel_positioning = false;
-  } else {
+  } else if (!base::CommandLine::ForCurrentProcess()->HasSwitch(
+                 switches::kDisableFontSubpixelPositioning)) {
 #if !defined(OS_CHROMEOS)
     params.subpixel_positioning = actual_query.device_scale_factor > 1.0f;
 #else
-    params.subpixel_positioning = false;
+    // We want to enable subpixel positioning for fractional dsf.
+    params.subpixel_positioning =
+        std::abs(std::round(actual_query.device_scale_factor) -
+                 actual_query.device_scale_factor) >
+        std::numeric_limits<float>::epsilon();
 #endif  // !defined(OS_CHROMEOS)
 
     // To enable subpixel positioning, we need to disable hinting.

ui/gfx/font_render_params_linux_unittest.cc

@@ -310,9 +310,20 @@ TEST_F(FontRenderParamsTest, ForceSubpixelPositioning) {
     FontRenderParams params =
         GetFontRenderParams(FontRenderParamsQuery(), NULL);
     EXPECT_TRUE(params.antialiasing);
+    EXPECT_TRUE(params.subpixel_positioning);
+    SetFontRenderParamsDeviceScaleFactor(1.0f);
+  }
+  ClearFontRenderParamsCacheForTest();
+  SetFontRenderParamsDeviceScaleFactor(2.f);
+  // Subpixel positioning should be forced on non-Chrome-OS.
+  {
+    FontRenderParams params =
+        GetFontRenderParams(FontRenderParamsQuery(), nullptr);
+    EXPECT_TRUE(params.antialiasing);
 #if !defined(OS_CHROMEOS)
     EXPECT_TRUE(params.subpixel_positioning);
 #else
+    // Integral scale factor does not require subpixel positioning.
     EXPECT_FALSE(params.subpixel_positioning);
 #endif  // !defined(OS_CHROMEOS)
     SetFontRenderParamsDeviceScaleFactor(1.0f);

ui/gfx/switches.cc

@@ -18,6 +18,11 @@ const char kDisableDirectWriteForUI[] = "disable-directwrite-for-ui";
 const char kEnableHarfBuzzRenderText[] = "enable-harfbuzz-rendertext";
 #endif
 
+// Force disables font subpixel positioning. This affects the character glyph
+// sharpness, kerning, hinting and layout.
+const char kDisableFontSubpixelPositioning[] =
+    "disable-font-subpixel-positioning";
+
 // Run in headless mode, i.e., without a UI or display server dependencies.
 const char kHeadless[] = "headless";
 

ui/gfx/switches.h

@@ -19,6 +19,8 @@ GFX_SWITCHES_EXPORT extern const char kDisableDirectWriteForUI[];
 GFX_SWITCHES_EXPORT extern const char kEnableHarfBuzzRenderText[];
 #endif
 
+GFX_SWITCHES_EXPORT extern const char kDisableFontSubpixelPositioning[];
+
 GFX_SWITCHES_EXPORT extern const char kHeadless[];
 
 }  // namespace switches