如何更改ExoPlayer字幕在安卓系统中的位置？

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.Surface;

import com.google.android.exoplayer2.Renderer;
import com.google.android.exoplayer2.format.MediaFormat;
import com.google.android.exoplayer2.util.Util;

public class CustomSubtitleRenderer implements Renderer {

    private final Paint paint = new Paint();
    private int xPosition = 100; // 自定义水平位置
    private int yPosition = 100; // 自定义垂直位置

    @Override
    public int getTrackType() {
        return Util.SDK_INT >= 24 ? C.TRACK_TYPE_TEXT : C.TRACK_TYPE_SUBTITLE;
    }

    @Override
    public void render(long positionUs, long elapsedRealtimeUs, boolean isLastFrame, MediaCodecAdapter mediaCodecAdapter, Surface surface) {
        if (surface == null) {
            return;
        }

        Canvas canvas = surface.lockCanvas(null);
        if (canvas != null) {
            try {
                // 清除画布
                canvas.drawColor(Color.BLACK);

                // 绘制字幕
                String subtitleText = "Example Subtitle";
                paint.setColor(Color.WHITE);
                paint.setTextSize(30);
                canvas.drawText(subtitleText, xPosition, yPosition, paint);
            } finally {
                surface.unlockCanvasAndPost(canvas);
            }
        }
    }

    @Override
    public void onEnabled(boolean enabled) {
        // 启用/禁用渲染器时的逻辑
    }

    @Override
    public void onDisabled() {
        // 启用/禁用渲染器时的逻辑
    }

    @Override
    public MediaFormat getOutputFormat(int trackIndex) {
        return MediaFormat.createTextSampleFormat(trackIndex, MimeTypes.APPLICATION_SUBRIP, MediaFormat.NO_VALUE, MediaFormat.NO_VALUE, C.SELECTION_FLAG_DEFAULT);
    }

    @Override
    public void onConfigurationChanged(Configuration configuration) {
        // 配置变化时的逻辑
    }

    @Override
    public void onReleased() {
        // 释放资源时的逻辑
    }
}