src/android/src/com/google/android/inputmethod/japanese/view/VerticalInnerDropShadowDrawable.java

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package org.mozc.android.inputmethod.japanese.view;

import com.google.common.base.Optional;

import android.graphics.Canvas;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.Shader.TileMode;

/**
 * Drawable for drop shadow on top and bottom of the boundary.
 */
public class VerticalInnerDropShadowDrawable extends BaseBackgroundDrawable {

  private final int shadowSize;
  private Optional<LinearGradient> topShadow = Optional.absent();
  private Optional<LinearGradient> bottomShadow = Optional.absent();
  private final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

  public VerticalInnerDropShadowDrawable(
      int leftPadding, int topPadding, int rightPadding, int bottomPadding,
      int shadowSize) {
    super(leftPadding, topPadding, rightPadding, bottomPadding);
    this.shadowSize = shadowSize;
  }

  @Override
  public void draw(Canvas canvas) {
    if (isCanvasRectEmpty()) {
      return;
    }

    Rect rect = getCanvasRect();
    if (topShadow.isPresent()) {
      paint.setShader(topShadow.get());
      canvas.drawRect(rect, paint);
    }

    if (bottomShadow.isPresent()) {
      paint.setShader(bottomShadow.get());
      canvas.drawRect(rect, paint);
    }
  }

  @Override
  protected void onBoundsChange(Rect bounds) {
    super.onBoundsChange(bounds);
    if (isCanvasRectEmpty()) {
      topShadow = Optional.absent();
      bottomShadow = Optional.absent();
      return;
    }

    Rect canvasRect = getCanvasRect();
    topShadow = Optional.of(new LinearGradient(
        0, canvasRect.top, 0, Math.min(canvasRect.bottom, canvasRect.top + shadowSize),
        0xA6000000, 0x00000000, TileMode.CLAMP));
    bottomShadow = Optional.of(new LinearGradient(
        0, Math.max(canvasRect.top, canvasRect.bottom - shadowSize), 0, canvasRect.bottom,
        0x00000000, 0xA6000000, TileMode.CLAMP));
  }
}