Eliminate hardcoded scale factor in a11y scroll

ci/licenses_golden/licenses_flutter

@@ -2390,6 +2390,9 @@ ORIGIN: ../../../flutter/third_party/accessibility/base/win/atl_module.h + ../..
 TYPE: LicenseType.bsd
 FILE: ../../../flutter/third_party/accessibility/base/auto_reset.h
 FILE: ../../../flutter/third_party/accessibility/base/win/atl_module.h
+FILE: ../../../flutter/third_party/accessibility/base/win/display.cc
+FILE: ../../../flutter/third_party/accessibility/base/win/display.h
+FILE: ../../../flutter/third_party/accessibility/base/win/display_unittest.cc
 FILE: ../../../flutter/third_party/accessibility/base/win/enum_variant.cc
 FILE: ../../../flutter/third_party/accessibility/base/win/enum_variant.h
 FILE: ../../../flutter/third_party/accessibility/base/win/enum_variant_unittest.cc

third_party/accessibility/BUILD.gn

@@ -81,6 +81,7 @@ if (enable_unittests) {
           "ax/platform/ax_platform_node_win_unittest.cc",
           "base/win/dispatch_stub.cc",
           "base/win/dispatch_stub.h",
+          "base/win/display_unittest.cc",
           "base/win/scoped_bstr_unittest.cc",
           "base/win/scoped_safearray_unittest.cc",
           "base/win/scoped_variant_unittest.cc",

third_party/accessibility/ax/BUILD.gn

@@ -99,6 +99,7 @@ source_set("ax") {
     ]
     libs = [
       "oleacc.lib",
+      "shcore.lib",
       "uiautomationcore.lib",
     ]
   }

third_party/accessibility/ax/platform/ax_platform_node_win.cc

@@ -31,10 +31,12 @@
 #include "ax_fragment_root_win.h"
 #include "ax_platform_node_delegate.h"
 #include "ax_platform_node_delegate_utils_win.h"
+#include "shellscalingapi.h"
 #include "uia_registrar_win.h"
 
 #include "base/logging.h"
 #include "base/win/atl_module.h"
+#include "base/win/display.h"
 #include "gfx/geometry/rect_conversions.h"
 
 // From ax.constants.mojom
@@ -476,9 +478,7 @@ gfx::Vector2d AXPlatformNodeWin::CalculateUIAScrollPoint(
 
   const HWND hwnd = GetDelegate()->GetTargetForNativeAccessibilityEvent();
   BASE_DCHECK(hwnd);
-  // TODO(gw280): https://github.com/flutter/flutter/issues/78798
-  // Support scale factors
-  const float scale_factor = 1.0f;
+  const float scale_factor = base::win::GetScaleFactorForHWND(hwnd);
   const int small_change =
       base::ClampRound(kSmallScrollIncrement * scale_factor);
 

third_party/accessibility/base/BUILD.gn

@@ -26,6 +26,8 @@ source_set("base") {
     sources += [
       "win/atl.h",
       "win/atl_module.h",
+      "win/display.cc",
+      "win/display.h",
       "win/enum_variant.cc",
       "win/enum_variant.h",
       "win/scoped_bstr.cc",

third_party/accessibility/base/win/display.cc

@@ -0,0 +1,59 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/win/display.h"
+
+namespace base {
+namespace win {
+
+float GetScaleFactorForHWND(HWND hwnd) {
+  HMONITOR monitor = MonitorFromWindow(hwnd, MONITOR_DEFAULTTONEAREST);
+  DEVICE_SCALE_FACTOR scale_factor = DEVICE_SCALE_FACTOR_INVALID;
+  if (SUCCEEDED(GetScaleFactorForMonitor(monitor, &scale_factor))) {
+    return ScaleFactorToFloat(scale_factor);
+  }
+  return 1.0f;
+}
+
+float ScaleFactorToFloat(DEVICE_SCALE_FACTOR scale_factor) {
+  switch (scale_factor) {
+    case SCALE_100_PERCENT:
+      return 1.0f;
+    case SCALE_120_PERCENT:
+      return 1.2f;
+    case SCALE_125_PERCENT:
+      return 1.25f;
+    case SCALE_140_PERCENT:
+      return 1.4f;
+    case SCALE_150_PERCENT:
+      return 1.5f;
+    case SCALE_160_PERCENT:
+      return 1.6f;
+    case SCALE_175_PERCENT:
+      return 1.75f;
+    case SCALE_180_PERCENT:
+      return 1.8f;
+    case SCALE_200_PERCENT:
+      return 2.0f;
+    case SCALE_225_PERCENT:
+      return 2.25f;
+    case SCALE_250_PERCENT:
+      return 2.5f;
+    case SCALE_300_PERCENT:
+      return 3.0f;
+    case SCALE_350_PERCENT:
+      return 3.5f;
+    case SCALE_400_PERCENT:
+      return 4.0f;
+    case SCALE_450_PERCENT:
+      return 4.5f;
+    case SCALE_500_PERCENT:
+      return 5.0f;
+    default:
+      return 1.0f;
+  }
+}
+
+}  // namespace win
+}  // namespace base

third_party/accessibility/base/win/display.h

@@ -0,0 +1,23 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_WIN_DISPLAY_H_
+#define BASE_WIN_DISPLAY_H_
+
+#include <windows.h>
+
+#include <shellscalingapi.h>
+
+#include "base/base_export.h"
+
+namespace base {
+namespace win {
+
+float GetScaleFactorForHWND(HWND hwnd);
+float ScaleFactorToFloat(DEVICE_SCALE_FACTOR scale_factor);
+
+}  // namespace win
+}  // namespace base
+
+#endif  // BASE_WIN_DISPLAY_H_

third_party/accessibility/base/win/display_unittest.cc

@@ -0,0 +1,32 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/win/display.h"
+
+#include "gtest/gtest.h"
+
+namespace base {
+namespace win {
+
+TEST(Display, ScaleFactorToFloat) {
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_100_PERCENT), 1.00f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_120_PERCENT), 1.20f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_125_PERCENT), 1.25f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_140_PERCENT), 1.40f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_150_PERCENT), 1.50f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_160_PERCENT), 1.60f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_175_PERCENT), 1.75f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_180_PERCENT), 1.80f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_200_PERCENT), 2.00f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_225_PERCENT), 2.25f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_250_PERCENT), 2.50f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_350_PERCENT), 3.50f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_400_PERCENT), 4.00f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_450_PERCENT), 4.50f);
+  EXPECT_EQ(ScaleFactorToFloat(SCALE_500_PERCENT), 5.00f);
+  EXPECT_EQ(ScaleFactorToFloat(DEVICE_SCALE_FACTOR_INVALID), 1.0f);
+}
+
+}  // namespace win
+}  // namespace base