Android: Add a maxFontSizeMultiplier prop to <Text> and <TextInput> (#23069)

Summary:
Equivalent of this iOS PR: #20915

Motivation:
----------

Whenever a user changes the system font size to its maximum allowable setting, React Native apps that allow font scaling can become unusable because the text gets too big. Experimenting with a native app like iMessage on iOS, the font size used for non-body text (e.g. header, navigational elements) is capped while the body text (e.g. text in the message bubbles) is allowed to grow.

This PR introduces a new prop on `<Text>` and `<TextInput>` called `maxFontSizeMultiplier`. This enables devs to set the maximum allowed text scale factor on a Text/TextInput. The default is 0 which means no limit.
Pull Request resolved: #23069

Differential Revision: D13748513

Pulled By: mdvacca

fbshipit-source-id: 8dd5d6d97bf79387d9a2236fa2e586ccb01afde9

Author: Adam Comella

ReactAndroid/src/main/java/com/facebook/react/uimanager/PixelUtil.java

@@ -7,6 +7,7 @@
 
 package com.facebook.react.uimanager;
 
+import android.util.DisplayMetrics;
 import android.util.TypedValue;
 
 /**
@@ -42,10 +43,21 @@ public static float toSPFromPixel(float value) {
    * Convert from SP to PX
    */
   public static float toPixelFromSP(float value) {
-    return TypedValue.applyDimension(
-        TypedValue.COMPLEX_UNIT_SP,
-        value,
-        DisplayMetricsHolder.getWindowDisplayMetrics());
+    return toPixelFromSP(value, Float.NaN);
+  }
+
+  /**
+   * Convert from SP to PX
+   */
+  public static float toPixelFromSP(float value, float maxFontScale) {
+    DisplayMetrics displayMetrics = DisplayMetricsHolder.getWindowDisplayMetrics();
+    float scaledDensity = displayMetrics.scaledDensity;
+    float currentFontScale = scaledDensity / displayMetrics.density;
+    if (maxFontScale >= 1 && maxFontScale < currentFontScale) {
+      scaledDensity = displayMetrics.density * maxFontScale;
+    }
+
+    return value * scaledDensity;
   }
 
   /**

ReactAndroid/src/main/java/com/facebook/react/uimanager/ViewProps.java

@@ -106,6 +106,7 @@ public class ViewProps {
   public static final String VISIBLE = "visible";
 
   public static final String ALLOW_FONT_SCALING = "allowFontScaling";
+  public static final String MAX_FONT_SIZE_MULTIPLIER = "maxFontSizeMultiplier";
   public static final String INCLUDE_FONT_PADDING = "includeFontPadding";
 
   public static final String BORDER_WIDTH = "borderWidth";

ReactAndroid/src/main/java/com/facebook/react/views/text/ReactBaseTextShadowNode.java

@@ -349,6 +349,14 @@ public void setAllowFontScaling(boolean allowFontScaling) {
     }
   }
 
+  @ReactProp(name = ViewProps.MAX_FONT_SIZE_MULTIPLIER, defaultFloat = Float.NaN)
+  public void setMaxFontSizeMultiplier(float maxFontSizeMultiplier) {
+    if (maxFontSizeMultiplier != mTextAttributes.getMaxFontSizeMultiplier()) {
+      mTextAttributes.setMaxFontSizeMultiplier(maxFontSizeMultiplier);
+      markUpdated();
+    }
+  }
+
   @ReactProp(name = ViewProps.TEXT_ALIGN)
   public void setTextAlign(@Nullable String textAlign) {
     if (textAlign == null || "auto".equals(textAlign)) {

ReactAndroid/src/main/java/com/facebook/react/views/text/TextAttributes.java

@@ -7,6 +7,7 @@
 
 package com.facebook.react.views.text;
 
+import com.facebook.react.bridge.JSApplicationIllegalArgumentException;
 import com.facebook.react.uimanager.PixelUtil;
 import com.facebook.react.uimanager.ViewDefaults;
 
@@ -15,13 +16,17 @@
  * to child so inheritance can be implemented correctly. An example complexity that causes a prop
  * to end up in TextAttributes is when multiple props need to be considered together to determine
  * the rendered aka effective value. For example, to figure out the rendered/effective font size,
- * you need to take into account the fontSize and allowFontScaling props.
+ * you need to take into account the fontSize, maxFontSizeMultiplier, and allowFontScaling props.
  */
 public class TextAttributes {
+  // Setting the default to 0 indicates that there is no max.
+  public static final float DEFAULT_MAX_FONT_SIZE_MULTIPLIER = 0.0f;
+
   private boolean mAllowFontScaling = true;
   private float mFontSize = Float.NaN;
   private float mLineHeight = Float.NaN;
   private float mLetterSpacing = Float.NaN;
+  private float mMaxFontSizeMultiplier = Float.NaN;
   private float mHeightOfTallestInlineImage = Float.NaN;
 
   public TextAttributes() {
@@ -37,6 +42,7 @@ public TextAttributes applyChild(TextAttributes child) {
     result.mFontSize = !Float.isNaN(child.mFontSize) ? child.mFontSize : mFontSize;
     result.mLineHeight = !Float.isNaN(child.mLineHeight) ? child.mLineHeight : mLineHeight;
     result.mLetterSpacing = !Float.isNaN(child.mLetterSpacing) ? child.mLetterSpacing : mLetterSpacing;
+    result.mMaxFontSizeMultiplier = !Float.isNaN(child.mMaxFontSizeMultiplier) ? child.mMaxFontSizeMultiplier : mMaxFontSizeMultiplier;
     result.mHeightOfTallestInlineImage = !Float.isNaN(child.mHeightOfTallestInlineImage) ? child.mHeightOfTallestInlineImage : mHeightOfTallestInlineImage;
 
     return result;
@@ -77,6 +83,17 @@ public void setLetterSpacing(float value) {
     mLetterSpacing = value;
   }
 
+  public float getMaxFontSizeMultiplier() {
+    return mMaxFontSizeMultiplier;
+  }
+
+  public void setMaxFontSizeMultiplier(float maxFontSizeMultiplier) {
+    if (maxFontSizeMultiplier != 0 && maxFontSizeMultiplier < 1) {
+      throw new JSApplicationIllegalArgumentException("maxFontSizeMultiplier must be NaN, 0, or >= 1");
+    }
+    mMaxFontSizeMultiplier = maxFontSizeMultiplier;
+  }
+
   public float getHeightOfTallestInlineImage() {
     return mHeightOfTallestInlineImage;
   }
@@ -94,7 +111,7 @@ public void setHeightOfTallestInlineImage(float value) {
   public int getEffectiveFontSize() {
     float fontSize = !Float.isNaN(mFontSize) ? mFontSize : ViewDefaults.FONT_SIZE_SP;
     return mAllowFontScaling
-      ? (int) Math.ceil(PixelUtil.toPixelFromSP(fontSize))
+      ? (int) Math.ceil(PixelUtil.toPixelFromSP(fontSize, getEffectiveMaxFontSizeMultiplier()))
       : (int) Math.ceil(PixelUtil.toPixelFromDIP(fontSize));
   }
 
@@ -104,7 +121,7 @@ public float getEffectiveLineHeight() {
     }
 
     float lineHeight = mAllowFontScaling
-      ? PixelUtil.toPixelFromSP(mLineHeight)
+      ? PixelUtil.toPixelFromSP(mLineHeight, getEffectiveMaxFontSizeMultiplier())
       : PixelUtil.toPixelFromDIP(mLineHeight);
 
     // Take into account the requested line height
@@ -121,14 +138,21 @@ public float getEffectiveLetterSpacing() {
     }
 
     float letterSpacingPixels = mAllowFontScaling
-      ? PixelUtil.toPixelFromSP(mLetterSpacing)
+      ? PixelUtil.toPixelFromSP(mLetterSpacing, getEffectiveMaxFontSizeMultiplier())
       : PixelUtil.toPixelFromDIP(mLetterSpacing);
 
     // `letterSpacingPixels` and `getEffectiveFontSize` are both in pixels,
     // yielding an accurate em value.
     return letterSpacingPixels / getEffectiveFontSize();
   }
 
+  // Never returns NaN
+  public float getEffectiveMaxFontSizeMultiplier() {
+    return !Float.isNaN(mMaxFontSizeMultiplier)
+      ? mMaxFontSizeMultiplier
+      : DEFAULT_MAX_FONT_SIZE_MULTIPLIER;
+  }
+
   public String toString() {
     return (
       "TextAttributes {"
@@ -140,6 +164,8 @@ public String toString() {
       + "\n  getEffectiveLetterSpacing(): " + getEffectiveLetterSpacing()
       + "\n  getLineHeight(): " + getLineHeight()
       + "\n  getEffectiveLineHeight(): " + getEffectiveLineHeight()
+      + "\n  getMaxFontSizeMultiplier(): " + getMaxFontSizeMultiplier()
+      + "\n  getEffectiveMaxFontSizeMultiplier(): " + getEffectiveMaxFontSizeMultiplier()
       + "\n}"
     );
   }

ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactEditText.java

@@ -647,6 +647,13 @@ public void setFontSize(float fontSize) {
     applyTextAttributes();
   }
 
+  public void setMaxFontSizeMultiplier(float maxFontSizeMultiplier) {
+    if (maxFontSizeMultiplier != mTextAttributes.getMaxFontSizeMultiplier()) {
+      mTextAttributes.setMaxFontSizeMultiplier(maxFontSizeMultiplier);
+      applyTextAttributes();
+    }
+  }
+
   protected void applyTextAttributes() {
     // In general, the `getEffective*` functions return `Float.NaN` if the
     // property hasn't been set.

ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactTextInputManager.java

@@ -217,6 +217,11 @@ public void setFontFamily(ReactEditText view, String fontFamily) {
     view.setTypeface(newTypeface);
   }
 
+  @ReactProp(name = ViewProps.MAX_FONT_SIZE_MULTIPLIER, defaultFloat = Float.NaN)
+  public void setMaxFontSizeMultiplier(ReactEditText view, float maxFontSizeMultiplier) {
+    view.setMaxFontSizeMultiplier(maxFontSizeMultiplier);
+  }
+
   /**
   /* This code was taken from the method setFontWeight of the class ReactTextShadowNode
   /* TODO: Factor into a common place they can both use