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

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

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

/**
 * Drawable to render a circular highlight at the center of the key background.
 *
 */
public class CenterCircularHighlightDrawable extends BaseBackgroundDrawable {
  // According to the original design mock, the ratio of radius to height is 0.23.
  private static final float RADIUS_RATIO = 0.23f;

  private final int baseColor;
  private final int shadeColor;

  private final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
  private float centerX;
  private float centerY;
  private float radius;

  public CenterCircularHighlightDrawable(
      int leftPadding, int topPadding, int rightPadding, int bottomPadding,
      int baseColor, int shadeColor) {
    super(leftPadding, topPadding, rightPadding, bottomPadding);
    this.baseColor = baseColor;
    this.shadeColor = shadeColor;
  }

  @Override
  public void draw(Canvas canvas) {
    canvas.drawCircle(centerX, centerY, radius, paint);
  }

  @Override
  protected void onBoundsChange(Rect rect) {
    super.onBoundsChange(rect);
    Rect canvasRect = getCanvasRect();
    centerX = canvasRect.exactCenterX();
    centerY = canvasRect.exactCenterY();
    radius = canvasRect.height() * RADIUS_RATIO;

    // According to the original design mock, the circle has inner shadow,
    // whose width is about 20% of the radius.
    paint.setShader(new RadialGradient(centerX, centerY, radius,
                                       new int[] { baseColor, shadeColor },
                                       new float[] { 0.8f, 1.0f },
                                       TileMode.CLAMP));
  }
}