适合单个Activity 的水印功能。

package com.flushao.util;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.drawable.Drawable;
import android.util.Log;

import androidx.annotation.IntRange;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import java.util.List;

/**
 * @author flushao
 * <p>
 * 添加水印的背景图
 */
public class WaterMarkBgView extends Drawable {

    private final Paint paint = new Paint();
    private List<String> labels;
    private Context context;
    private int degrees = 0;        // 角度
    private int fontSize = 12;       // 字体大小 单位sp
    private int line = 8;       // 多少行
    private int lineNumb = 10;  // 每行多少个

    /**
     * @param context  上下文
     * @param labels   水印文字列表
     * @param degrees  水印角度
     * @param fontSize 水印文字大小
     */
    public WaterMarkBgView(Context context, List<String> labels, int degrees, int fontSize) {
        this(context, labels, 5, 6, degrees, fontSize);
    }

    /**
     * @param context  上下文
     * @param labels   水印文字列表
     * @param degrees  水印角度
     * @param line     行数
     * @param lineNumb 每行水印数
     * @param fontSize 水印文字大小
     */
    public WaterMarkBgView(Context context, List<String> labels, int line, int lineNumb, int degrees, int fontSize) {
        this.labels = labels;
        this.context = context;
        this.degrees = degrees;
        this.fontSize = fontSize;
        this.line = line;
        this.lineNumb = lineNumb;
        // 做一些边缘检测

        if (fontSize > 24) {
            this.fontSize = 24;
            Logd.e("WaterMarkBgView", "水印字体过大将影响观感,建议使用 16 ~ 20 ！！！！");
            try {
                throw new Exception("水印字体过大将影响观感,建议使用 16 ~ 20 ！！！");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        if (degrees > 30) {
            this.degrees = 30;
            Logd.e("WaterMarkBgView", "建议水印倾斜角度设置在 20 度！！！！");
            try {
                throw new Exception("建议水印倾斜角度设置在 20 度！！！！");
            } catch (Exception e) {
                e.printStackTrace();
            }
        } else if (degrees < -30) {
            this.degrees = -30;
            Logd.e("WaterMarkBgView", "建议水印倾斜角度设置在 20 度！！！！");
            try {
                throw new Exception("建议水印倾斜角度设置在 20 度！！！！");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }

    public static int sp2px(Context context, float spValue) {
        final float fontScale = context.getResources().getDisplayMetrics().scaledDensity;
        return (int) (spValue * fontScale + 0.5f);
    }

    @Override
    public void draw(@NonNull Canvas canvas) {

        int width = getBounds().right;
        int height = getBounds().bottom;

        // 画布背景色
        canvas.drawColor(Color.parseColor("#00000000"));
        // 水印文字的颜色
        paint.setColor(Color.parseColor("#AEAEAE"));
        paint.setAntiAlias(true);
        paint.setAlpha(60);
        paint.setTextSize(sp2px(context, fontSize));
        canvas.save();
        canvas.rotate(degrees);
        // 开始绘制水印
        float textWidth = paint.measureText(labels.get(0));
        // 每一个的起始高度为： （总高度 - (最后一条的高度 + 每个水印列表的间距)  ) / 水印条数 - 1
        float everyTextLineHeight = (float) (height - (sp2px(context, fontSize)  * labels.size() + 5* labels.size())) / (line - 1);
        float everyTextWidth = (width - textWidth) / (lineNumb - 1);
        if (degrees == 0) {
            // 没角度直接画
            for (int i = 0; i < line; i++) {
                float positionY = i * everyTextLineHeight + sp2px(context, fontSize);
                for (int j = 0; j < lineNumb; j++) {
                    float positionX = j * everyTextWidth;
                    for (int l = 0; l < labels.size(); l++) {
                        canvas.drawText(labels.get(l), positionX, positionY + sp2px(context, fontSize) * l + 3, paint);
                    }
                }
            }
        }else {
            // 如果有角度，那就把其他三个象限都画上,并且以左上为起点
            for (int i = 0; i < line * 2; i++) {
                float positionY = i * everyTextLineHeight + sp2px(context, fontSize) - height;
                for (int j = 0; j < lineNumb * 2; j++) {
                    float positionX = j * everyTextWidth - width;
                    for (int l = 0; l < labels.size(); l++) {
                        canvas.drawText(labels.get(l), positionX, positionY + sp2px(context, fontSize) * l + 5, paint);
                    }
                }
            }
        }

        canvas.restore();
    }

    @Override
    public void setAlpha(@IntRange(from = 0, to = 255) int alpha) {
    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {
    }

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