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

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

import android.graphics.BlurMaskFilter;
import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.Rect;
import android.graphics.BlurMaskFilter.Blur;
import android.graphics.Paint.Style;
import android.graphics.Shader.TileMode;
import android.graphics.drawable.Drawable;

/**
 * The light (indicator) mark for ALT key on qwerty layout.
 *
 */
public class LightIconDrawable extends Drawable {
  private final float topOffset;
  private final float rightOffset;

  private final int lightColor;
  private final int darkColor;
  private final float radius;

  private float centerX;
  private float centerY;

  private final Paint basePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
  private final Paint shadePaint = new Paint(Paint.ANTI_ALIAS_FLAG);

  public LightIconDrawable(float topOffset, float rightOffset,
                           int lightColor, int darkColor, int shadeColor, float radius) {
    this.topOffset = topOffset;
    this.rightOffset = rightOffset;
    this.lightColor = lightColor;
    this.darkColor = darkColor;
    this.radius = radius;

    if (lightColor == darkColor) {
      basePaint.setColor(lightColor);
    }

    shadePaint.setStyle(Style.STROKE);
    shadePaint.setStrokeWidth(1);
    shadePaint.setMaskFilter(new BlurMaskFilter(2, Blur.INNER));
    shadePaint.setColor(shadeColor);
  }

  /* (non-Javadoc)
   * @see android.graphics.drawable.Drawable#draw(android.graphics.Canvas)
   */
  @Override
  public void draw(Canvas canvas) {
    canvas.drawCircle(centerX, centerY, radius, basePaint);
    canvas.drawCircle(centerX, centerY, radius, shadePaint);
  }

  @Override
  protected void onBoundsChange(Rect bound) {
    super.onBoundsChange(bound);

    centerX = bound.right - rightOffset;
    centerY = bound.top + topOffset;

    if (lightColor != darkColor) {
      float top = centerY - radius;
      // Hard coded parameters are based on design mock.
      basePaint.setShader(new LinearGradient(
          centerX, top, centerX + 2, top + 8, lightColor, darkColor, TileMode.CLAMP));
    }
  }

  @Override
  public int getOpacity() {
    return PixelFormat.TRANSLUCENT;
  }

  @Override
  public void setAlpha(int alpha) {
  }

  @Override
  public void setColorFilter(ColorFilter cf) {
  }
}