Android: Send <Text> metrics in onTextLayout events

Summary:
@public
As we're doing in D9440914 (OSS 64a52532fe), send text metrics in an onTextLayout callback. These can be used by surrounding views for doing complicated layout like:
- displaying a cursor at the end of text
- vertical centering using capheight-baseline

This right now isn't very performant but is only done when `onTextLayout` is set. I plan to optimize it with a capheight and xheight cache in a follow up diff.

Reviewed By: achen1

Differential Revision: D9585613

fbshipit-source-id: aa20535b8371d5aecf15822d66a0d973c9a7eeda

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

@@ -0,0 +1,50 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.views.text;
+
+import android.content.Context;
+import android.graphics.Rect;
+import android.text.Layout;
+import android.text.TextPaint;
+import android.util.DisplayMetrics;
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.WritableArray;
+import com.facebook.react.bridge.WritableMap;
+
+public class FontMetricsUtil {
+  public static WritableArray getFontMetrics(CharSequence text, Layout layout, TextPaint paint, Context context) {
+    DisplayMetrics dm = context.getResources().getDisplayMetrics();
+    WritableArray lines = Arguments.createArray();
+    for (int i = 0; i < layout.getLineCount(); i++) {
+      Rect bounds = new Rect();
+      layout.getLineBounds(i, bounds);
+
+      WritableMap line = Arguments.createMap();
+      TextPaint paintCopy = new TextPaint(paint);
+      paintCopy.setTextSize(paintCopy.getTextSize() * 100);
+      Rect capHeightBounds = new Rect();
+      paintCopy.getTextBounds("T", 0, 1, capHeightBounds);
+      Rect xHeightBounds = new Rect();
+      paintCopy.getTextBounds("x", 0, 1, xHeightBounds);
+      line.putDouble("x", bounds.left / dm.density);
+      line.putDouble("y", bounds.top / dm.density);
+      line.putDouble("width", layout.getLineWidth(i) / dm.density);
+      line.putDouble("height", bounds.height() / dm.density);
+      line.putDouble("descender", layout.getLineDescent(i) / dm.density);
+      line.putDouble("ascender", -layout.getLineAscent(i) / dm.density);
+      line.putDouble("baseline", layout.getLineBaseline(i) / dm.density);
+      line.putDouble(
+          "capHeight", capHeightBounds.height() / 100 * paint.getTextSize() / dm.density);
+      line.putDouble("xHeight", xHeightBounds.height() / 100 * paint.getTextSize() / dm.density);
+      line.putString(
+          "text", text.subSequence(layout.getLineStart(i), layout.getLineEnd(i)).toString());
+      lines.pushMap(line);
+    }
+    return lines;
+  }
+}

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

@@ -7,6 +7,7 @@
 
 package com.facebook.react.views.text;
 
+import android.graphics.Rect;
 import android.os.Build;
 import android.text.BoringLayout;
 import android.text.Layout;
@@ -14,13 +15,19 @@ import android.text.Spannable;
 import android.text.Spanned;
 import android.text.StaticLayout;
 import android.text.TextPaint;
+import android.util.DisplayMetrics;
 import android.view.Gravity;
 import android.widget.TextView;
 import com.facebook.infer.annotation.Assertions;
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.WritableArray;
+import com.facebook.react.bridge.WritableMap;
 import com.facebook.react.uimanager.LayoutShadowNode;
 import com.facebook.react.uimanager.ReactShadowNodeImpl;
 import com.facebook.react.uimanager.Spacing;
 import com.facebook.react.uimanager.UIViewOperationQueue;
+import com.facebook.react.uimanager.annotations.ReactProp;
+import com.facebook.react.uimanager.events.RCTEventEmitter;
 import com.facebook.yoga.YogaConstants;
 import com.facebook.yoga.YogaDirection;
 import com.facebook.yoga.YogaMeasureFunction;
@@ -44,6 +51,8 @@ public class ReactTextShadowNode extends ReactBaseTextShadowNode {
 
   private @Nullable Spannable mPreparedSpannableText;
 
+  private boolean mShouldNotifyOnTextLayout;
+
   private final YogaMeasureFunction mTextMeasureFunction =
       new YogaMeasureFunction() {
         @Override
@@ -127,11 +136,18 @@ public class ReactTextShadowNode extends ReactBaseTextShadowNode {
             }
           }
 
-          if (mNumberOfLines != UNSET &&
-              mNumberOfLines < layout.getLineCount()) {
-            return YogaMeasureOutput.make(
-                layout.getWidth(),
-                layout.getLineBottom(mNumberOfLines - 1));
+          if (mShouldNotifyOnTextLayout) {
+            WritableArray lines =
+              FontMetricsUtil.getFontMetrics(text, layout, sTextPaintInstance, getThemedContext());
+            WritableMap event = Arguments.createMap();
+            event.putArray("lines", lines);
+            getThemedContext()
+                .getJSModule(RCTEventEmitter.class)
+                .receiveEvent(getReactTag(), "topTextLayout", event);
+          }
+
+          if (mNumberOfLines != UNSET && mNumberOfLines < layout.getLineCount()) {
+            return YogaMeasureOutput.make(layout.getWidth(), layout.getLineBottom(mNumberOfLines - 1));
           } else {
             return YogaMeasureOutput.make(layout.getWidth(), layout.getHeight());
           }
@@ -223,4 +239,9 @@ public class ReactTextShadowNode extends ReactBaseTextShadowNode {
       uiViewOperationQueue.enqueueUpdateExtraData(getReactTag(), reactTextUpdate);
     }
   }
+
+  @ReactProp(name = "onTextLayout")
+  public void setShouldNotifyOnTextLayout(boolean shouldNotifyOnTextLayout) {
+    mShouldNotifyOnTextLayout = shouldNotifyOnTextLayout;
+  }
 }

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

@@ -8,9 +8,12 @@
 package com.facebook.react.views.text;
 
 import android.text.Spannable;
+import com.facebook.react.common.MapBuilder;
 import com.facebook.react.common.annotations.VisibleForTesting;
 import com.facebook.react.module.annotations.ReactModule;
 import com.facebook.react.uimanager.ThemedReactContext;
+import java.util.Map;
+import javax.annotation.Nullable;
 
 /**
  * Concrete class for {@link ReactTextAnchorViewManager} which represents view managers of anchor
@@ -58,4 +61,9 @@ public class ReactTextViewManager
     super.onAfterUpdateTransaction(view);
     view.updateView();
   }
+
+  @Override
+  public @Nullable Map getExportedCustomDirectEventTypeConstants() {
+    return MapBuilder.of("topTextLayout", MapBuilder.of("registrationName", "onTextLayout"));
+  }
 }