[TextField] Fix label cutout doesn't work on API < 18

Android framework Canvas.clipRect() has a bug with Region.Op.DIFFERENCE when handling bounds.left on APIs lower than 18, which causes text field outlines are still drawn over the label on lower APIs, despite the label area is supposed to be cut out.

Fixes this by bringing back the old solution we were using - "painting out" the label area after the stroke is drawn. Since the implementation is quite complicated, this CL also splits the CutoutDrawable to two inner impl classes to have a better code structure.

Resolves #2811 (comment)

PiperOrigin-RevId: 482013070

Author: drchen

lib/java/com/google/android/material/textfield/CutoutDrawable.java

@@ -16,11 +16,18 @@
 
 package com.google.android.material.textfield;
 
+import android.annotation.TargetApi;
 import android.graphics.Canvas;
+import android.graphics.Color;
+import android.graphics.Paint;
+import android.graphics.Paint.Style;
+import android.graphics.PorterDuff.Mode;
+import android.graphics.PorterDuffXfermode;
 import android.graphics.RectF;
 import android.graphics.Region.Op;
 import android.os.Build.VERSION;
 import android.os.Build.VERSION_CODES;
+import android.view.View;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import com.google.android.material.shape.MaterialShapeDrawable;
@@ -31,13 +38,15 @@
  * outline mode.
  */
 class CutoutDrawable extends MaterialShapeDrawable {
-  @NonNull private final RectF cutoutBounds;
+  @NonNull protected final RectF cutoutBounds;
 
-  CutoutDrawable() {
-    this(null);
+  static CutoutDrawable create(@Nullable ShapeAppearanceModel shapeAppearanceModel) {
+    return VERSION.SDK_INT >= VERSION_CODES.JELLY_BEAN_MR2
+        ? new ImplApi18(shapeAppearanceModel)
+        : new ImplApi14(shapeAppearanceModel);
   }
 
-  CutoutDrawable(@Nullable ShapeAppearanceModel shapeAppearanceModel) {
+  private CutoutDrawable(@Nullable ShapeAppearanceModel shapeAppearanceModel) {
     super(shapeAppearanceModel != null ? shapeAppearanceModel : new ShapeAppearanceModel());
     cutoutBounds = new RectF();
   }
@@ -67,20 +76,96 @@ void removeCutout() {
     setCutout(0, 0, 0, 0);
   }
 
-  @Override
-  protected void drawStrokeShape(@NonNull Canvas canvas) {
-    if (cutoutBounds.isEmpty()) {
-      super.drawStrokeShape(canvas);
-    } else {
-      // Saves the canvas so we can restore the clip after drawing the stroke.
-      canvas.save();
-      if (VERSION.SDK_INT >= VERSION_CODES.O) {
-        canvas.clipOutRect(cutoutBounds);
+  @TargetApi(VERSION_CODES.JELLY_BEAN_MR2)
+  private static class ImplApi18 extends CutoutDrawable {
+    ImplApi18(@Nullable ShapeAppearanceModel shapeAppearanceModel) {
+      super(shapeAppearanceModel);
+    }
+
+    @Override
+    protected void drawStrokeShape(@NonNull Canvas canvas) {
+      if (cutoutBounds.isEmpty()) {
+        super.drawStrokeShape(canvas);
       } else {
-        canvas.clipRect(cutoutBounds, Op.DIFFERENCE);
+        // Saves the canvas so we can restore the clip after drawing the stroke.
+        canvas.save();
+        if (VERSION.SDK_INT >= VERSION_CODES.O) {
+          canvas.clipOutRect(cutoutBounds);
+        } else {
+          canvas.clipRect(cutoutBounds, Op.DIFFERENCE);
+        }
+        super.drawStrokeShape(canvas);
+        canvas.restore();
       }
+    }
+  }
+
+  // Workaround: Canvas.clipRect() had a bug before API 18 - bound.left didn't work correctly
+  //             with Region.Op.DIFFERENCE. "Paints out" the cutout area instead on lower APIs.
+  private static class ImplApi14 extends CutoutDrawable {
+    private Paint cutoutPaint;
+    private int savedLayer;
+
+    ImplApi14(@Nullable ShapeAppearanceModel shapeAppearanceModel) {
+      super(shapeAppearanceModel);
+    }
+
+    @Override
+    public void draw(@NonNull Canvas canvas) {
+      preDraw(canvas);
+      super.draw(canvas);
+      postDraw(canvas);
+    }
+
+    @Override
+    protected void drawStrokeShape(@NonNull Canvas canvas) {
       super.drawStrokeShape(canvas);
-      canvas.restore();
+      canvas.drawRect(cutoutBounds, getCutoutPaint());
+    }
+
+    private Paint getCutoutPaint() {
+      if (cutoutPaint == null) {
+        cutoutPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
+        cutoutPaint.setStyle(Style.FILL_AND_STROKE);
+        cutoutPaint.setColor(Color.WHITE);
+        cutoutPaint.setXfermode(new PorterDuffXfermode(Mode.DST_OUT));
+      }
+      return cutoutPaint;
+    }
+
+    private void preDraw(@NonNull Canvas canvas) {
+      Callback callback = getCallback();
+
+      if (useHardwareLayer(callback)) {
+        View viewCallback = (View) callback;
+        // Make sure we're using a hardware layer.
+        if (viewCallback.getLayerType() != View.LAYER_TYPE_HARDWARE) {
+          viewCallback.setLayerType(View.LAYER_TYPE_HARDWARE, null);
+        }
+      } else {
+        // If we're not using a hardware layer, save the canvas layer.
+        saveCanvasLayer(canvas);
+      }
+    }
+
+    private void saveCanvasLayer(@NonNull Canvas canvas) {
+      if (VERSION.SDK_INT >= VERSION_CODES.LOLLIPOP) {
+        savedLayer = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), null);
+      } else {
+        savedLayer =
+            canvas.saveLayer(
+                0, 0, canvas.getWidth(), canvas.getHeight(), null, Canvas.ALL_SAVE_FLAG);
+      }
+    }
+
+    private void postDraw(@NonNull Canvas canvas) {
+      if (!useHardwareLayer(getCallback())) {
+        canvas.restoreToCount(savedLayer);
+      }
+    }
+
+    private boolean useHardwareLayer(Callback callback) {
+      return callback instanceof View;
     }
   }
 }

lib/java/com/google/android/material/textfield/TextInputLayout.java

@@ -785,7 +785,7 @@ private void assignBoxBackgroundByMode() {
         break;
       case BOX_BACKGROUND_OUTLINE:
         if (hintEnabled && !(boxBackground instanceof CutoutDrawable)) {
-          boxBackground = new CutoutDrawable(shapeAppearanceModel);
+          boxBackground = CutoutDrawable.create(shapeAppearanceModel);
         } else {
           boxBackground = new MaterialShapeDrawable(shapeAppearanceModel);
         }