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Fix text not scaling down when system fontScale < 1.0 (#54238)
Summary: Fixes #54168 In React Native 0.82.0, text on Android does not scale down when the system font scale is set to less than 1.0 (e.g., 85%). This regression was introduced when `PixelUtil.toPixelFromSP()` was changed to use `DisplayMetricsHolder.getScreenDisplayMetrics()` instead of `getWindowDisplayMetrics()` in commit [1ad2ec0](1ad2ec0). The issue occurs because: 1. **windowDisplayMetrics** is obtained from `context.resources.displayMetrics` and includes the system font scale from `Configuration` 2. **screenDisplayMetrics** is populated by `Display.getRealMetrics()`, which returns physical display metrics **without** the system font scale setting ([Reference](https://developer.android.com/reference/android/view/Display#getRealMetrics(android.util.DisplayMetrics))) When `getRealMetrics()` is called, it overwrites the `scaledDensity` value (which is `density * fontScale`), effectively resetting it to just `density` and losing the user's font scale preference. ## Changelog: <!-- Help reviewers and the release process by writing your own changelog entry. Pick one each for the category and type tags: [ANDROID|GENERAL|IOS|INTERNAL] [BREAKING|ADDED|CHANGED|DEPRECATED|REMOVED|FIXED|SECURITY] - Message For more details, see: https://reactnative.dev/contributing/changelogs-in-pull-requests --> [ANDROID] [FIXED] - Fix text not scaling down when system fontScale < 1.0 Pull Request resolved: #54238 Test Plan: https://github.com/kdwkr/rn-0.82.0-android-layout-scale Tested with this reproducer --- Reviewed By: javache Differential Revision: D85350263 Pulled By: alanleedev fbshipit-source-id: ff646cf0405f689ff2a9166a1474fdb8b1b85fd6
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‎packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/DisplayMetricsHolder.kt‎

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@@ -61,6 +61,7 @@ public object DisplayMetricsHolder {
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}
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@JvmStatic
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@Suppress("DEPRECATION")
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public fun initDisplayMetrics(context: Context) {
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val displayMetrics = context.resources.displayMetrics
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windowDisplayMetrics = displayMetrics
@@ -72,7 +73,11 @@ public object DisplayMetricsHolder {
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//
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// See:
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// http://developer.android.com/reference/android/view/Display.html#getRealMetrics(android.util.DisplayMetrics)
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@Suppress("DEPRECATION") wm.defaultDisplay.getRealMetrics(screenDisplayMetrics)
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wm.defaultDisplay.getRealMetrics(screenDisplayMetrics)
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// Preserve fontScale from the configuration because getRealMetrics() returns
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// physical display metrics without the system font scale setting.
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// This is needed for proper text scaling when fontScale < 1.0
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screenDisplayMetrics.scaledDensity = displayMetrics.scaledDensity
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DisplayMetricsHolder.screenDisplayMetrics = screenDisplayMetrics
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}
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‎packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/DisplayMetricsHolderTest.kt‎

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@@ -166,4 +166,18 @@ class DisplayMetricsHolderTest {
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assertThat(decodedWidth).isEqualTo(width)
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assertThat(decodedHeight).isEqualTo(height)
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}
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@Test
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fun initDisplayMetrics_preservesScaledDensityForFontScale() {
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val originalMetrics = context.resources.displayMetrics
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val customScaledDensity = originalMetrics.density * 0.85f // fontScale = 0.85
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originalMetrics.scaledDensity = customScaledDensity
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DisplayMetricsHolder.initDisplayMetrics(context)
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val screenMetrics = DisplayMetricsHolder.getScreenDisplayMetrics()
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assertThat(screenMetrics.scaledDensity).isEqualTo(customScaledDensity)
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}
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}

‎packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/PixelUtilTest.kt‎

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/*
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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package com.facebook.react.uimanager
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import android.content.Context
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import android.content.res.Configuration
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import android.content.res.Resources
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import android.util.DisplayMetrics
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import com.facebook.testutils.shadows.ShadowNativeLoader
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import com.facebook.testutils.shadows.ShadowSoLoader
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import kotlin.math.abs
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import org.assertj.core.api.Assertions.assertThat
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import org.junit.After
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import org.junit.Before
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import org.junit.Test
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import org.junit.runner.RunWith
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import org.mockito.kotlin.mock
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import org.mockito.kotlin.whenever
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import org.robolectric.RobolectricTestRunner
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import org.robolectric.RuntimeEnvironment
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import org.robolectric.annotation.Config
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@RunWith(RobolectricTestRunner::class)
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@Config(shadows = [ShadowSoLoader::class, ShadowNativeLoader::class])
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class PixelUtilTest {
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private lateinit var context: Context
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@Before
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fun setUp() {
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context = RuntimeEnvironment.getApplication()
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DisplayMetricsHolder.setWindowDisplayMetrics(null)
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DisplayMetricsHolder.setScreenDisplayMetrics(null)
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}
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@After
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fun tearDown() {
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DisplayMetricsHolder.setWindowDisplayMetrics(null)
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DisplayMetricsHolder.setScreenDisplayMetrics(null)
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}
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@Test
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fun toPixelFromSP_respectsFontScaleLessThanOne() {
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// Setup display metrics with fontScale < 1.0
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val displayMetrics = DisplayMetrics()
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displayMetrics.density = 3.0f
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displayMetrics.scaledDensity = 3.0f * 0.85f // fontScale = 0.85
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displayMetrics.widthPixels = 1080
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displayMetrics.heightPixels = 1920
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displayMetrics.densityDpi = DisplayMetrics.DENSITY_XXHIGH
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DisplayMetricsHolder.setWindowDisplayMetrics(displayMetrics)
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DisplayMetricsHolder.setScreenDisplayMetrics(displayMetrics)
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// Test that toPixelFromSP respects fontScale < 1.0
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val fontSize = 16f // 16sp
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val result = PixelUtil.toPixelFromSP(fontSize)
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// Expected: 16sp * 3.0 (density) * 0.85 (fontScale) = 40.8px
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val expected = fontSize * displayMetrics.scaledDensity
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assertThat(abs(result - expected)).isLessThan(0.1f)
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}
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@Test
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fun toPixelFromSP_respectsFontScaleGreaterThanOne() {
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// Setup display metrics with fontScale > 1.0
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val displayMetrics = DisplayMetrics()
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displayMetrics.density = 3.0f
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displayMetrics.scaledDensity = 3.0f * 1.3f // fontScale = 1.3
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displayMetrics.widthPixels = 1080
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displayMetrics.heightPixels = 1920
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displayMetrics.densityDpi = DisplayMetrics.DENSITY_XXHIGH
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DisplayMetricsHolder.setWindowDisplayMetrics(displayMetrics)
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DisplayMetricsHolder.setScreenDisplayMetrics(displayMetrics)
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// Test that toPixelFromSP respects fontScale > 1.0
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val fontSize = 16f // 16sp
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val result = PixelUtil.toPixelFromSP(fontSize)
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// Expected: 16sp * 3.0 (density) * 1.3 (fontScale) = 62.4px
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val expected = fontSize * displayMetrics.scaledDensity
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assertThat(abs(result - expected)).isLessThan(0.1f)
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}
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@Test
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fun toPixelFromSP_respectsMaxFontScale() {
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// Setup display metrics with high fontScale
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val displayMetrics = DisplayMetrics()
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displayMetrics.density = 3.0f
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displayMetrics.scaledDensity = 3.0f * 2.0f // fontScale = 2.0
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displayMetrics.widthPixels = 1080
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displayMetrics.heightPixels = 1920
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displayMetrics.densityDpi = DisplayMetrics.DENSITY_XXHIGH
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DisplayMetricsHolder.setWindowDisplayMetrics(displayMetrics)
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DisplayMetricsHolder.setScreenDisplayMetrics(displayMetrics)
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// Test that maxFontScale limits the scaling
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val fontSize = 16f // 16sp
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val maxFontScale = 1.5f
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val result = PixelUtil.toPixelFromSP(fontSize, maxFontScale)
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// With fontScale = 2.0, scaledValue would be 16 * 3.0 * 2.0 = 96px
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// But maxFontScale = 1.5 limits it to 16 * 3.0 * 1.5 = 72px
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val expected = fontSize * displayMetrics.density * maxFontScale
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assertThat(abs(result - expected)).isLessThan(0.1f)
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}
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@Test
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fun toPixelFromSP_doesNotApplyMaxFontScaleWhenFontScaleIsLess() {
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// Setup display metrics with low fontScale
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val displayMetrics = DisplayMetrics()
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displayMetrics.density = 3.0f
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displayMetrics.scaledDensity = 3.0f * 0.8f // fontScale = 0.8
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displayMetrics.widthPixels = 1080
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displayMetrics.heightPixels = 1920
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displayMetrics.densityDpi = DisplayMetrics.DENSITY_XXHIGH
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DisplayMetricsHolder.setWindowDisplayMetrics(displayMetrics)
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DisplayMetricsHolder.setScreenDisplayMetrics(displayMetrics)
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// Test that maxFontScale doesn't prevent scaling down
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val fontSize = 16f // 16sp
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val maxFontScale = 1.5f
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val result = PixelUtil.toPixelFromSP(fontSize, maxFontScale)
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// With fontScale = 0.8, scaledValue is 16 * 3.0 * 0.8 = 38.4px
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// maxFontScale limit would be 16 * 3.0 * 1.5 = 72px
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// min(38.4, 72) = 38.4px, so fontScale is respected
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val expected = fontSize * displayMetrics.scaledDensity
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assertThat(abs(result - expected)).isLessThan(0.1f)
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}
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@Test
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fun toPixelFromDIP_convertsCorrectly() {
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val displayMetrics = DisplayMetrics()
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displayMetrics.density = 3.0f
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displayMetrics.widthPixels = 1080
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displayMetrics.heightPixels = 1920
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displayMetrics.densityDpi = DisplayMetrics.DENSITY_XXHIGH
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DisplayMetricsHolder.setScreenDisplayMetrics(displayMetrics)
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val dipValue = 16f
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val result = PixelUtil.toPixelFromDIP(dipValue)
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// Expected: 16dp * 3.0 (density) = 48px
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val expected = dipValue * displayMetrics.density
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assertThat(abs(result - expected)).isLessThan(0.1f)
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}
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@Test
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fun initDisplayMetrics_preservesFontScale() {
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// Create a context with custom configuration
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val mockContext = mock<Context>()
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val mockResources = mock<Resources>()
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val configuration = Configuration()
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configuration.fontScale = 0.85f
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val displayMetrics = DisplayMetrics()
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displayMetrics.density = 3.0f
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displayMetrics.scaledDensity = 3.0f * 0.85f // fontScale = 0.85
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displayMetrics.widthPixels = 1080
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displayMetrics.heightPixels = 1920
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displayMetrics.densityDpi = DisplayMetrics.DENSITY_XXHIGH
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whenever(mockContext.resources).thenReturn(mockResources)
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whenever(mockResources.displayMetrics).thenReturn(displayMetrics)
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whenever(mockResources.configuration).thenReturn(configuration)
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whenever(mockContext.getSystemService(Context.WINDOW_SERVICE))
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.thenReturn(context.getSystemService(Context.WINDOW_SERVICE))
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// Initialize display metrics
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DisplayMetricsHolder.initDisplayMetrics(mockContext)
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val screenMetrics = DisplayMetricsHolder.getScreenDisplayMetrics()
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// Verify that scaledDensity (which includes fontScale) is preserved
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assertThat(abs(screenMetrics.scaledDensity - displayMetrics.scaledDensity)).isLessThan(0.01f)
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}
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}

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