与水印相关的源文件在这里: frameworks/base/services/core/java/com/android/server/wm/Watermark.java

参数包括：

• －要显示的字串（只能显示ASCII字符)
• －字符大小(dpi)
• －x轴偏移
• －y轴偏移
• －字体阴影颜色
• －字体颜色
• －字体阴影半径
• －字体阴影x轴偏移量
• －字体阴影y轴偏移量

class Watermark {
    Watermark(Display display, DisplayMetrics dm, SurfaceSession session, String[] tokens) {
        if (false) {
            Log.i(WindowManagerService.TAG, "*********************** WATERMARK");
            for (int i=0; i<tokens.length; i++) {
                Log.i(WindowManagerService.TAG, "  TOKEN #" + i + ": " + tokens[i]);
            }
        }

        mDisplay = display;
        mTokens = tokens;

        StringBuilder builder = new StringBuilder(32);
        int len = mTokens[0].length();
        len = len & ~1;
        for (int i=0; i<len; i+=2) {
            int c1 = mTokens[0].charAt(i);
            int c2 = mTokens[0].charAt(i+1);
            if (c1 >= 'a' && c1 <= 'f') c1 = c1 - 'a' + 10;
            else if (c1 >= 'A' && c1 <= 'F') c1 = c1 - 'A' + 10;
            else c1 -= '0';
            if (c2 >= 'a' && c2 <= 'f') c2 = c2 - 'a' + 10;
            else if (c2 >= 'A' && c2 <= 'F') c2 = c2 - 'A' + 10;
            else c2 -= '0';
            builder.append((char)(255-((c1*16)+c2)));
        }
        mText = builder.toString();
        if (false) {
            Log.i(WindowManagerService.TAG, "Final text: " + mText);
        }

        int fontSize = WindowManagerService.getPropertyInt(tokens, 1,
                TypedValue.COMPLEX_UNIT_DIP, 20, dm);

        mTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mTextPaint.setTextSize(fontSize);
        mTextPaint.setTypeface(Typeface.create(Typeface.SANS_SERIF, Typeface.BOLD));

        FontMetricsInt fm = mTextPaint.getFontMetricsInt();
        mTextWidth = (int)mTextPaint.measureText(mText);
        mTextHeight = fm.descent - fm.ascent;

        mDeltaX = WindowManagerService.getPropertyInt(tokens, 2,
                TypedValue.COMPLEX_UNIT_PX, mTextWidth*2, dm);
        mDeltaY = WindowManagerService.getPropertyInt(tokens, 3,
                TypedValue.COMPLEX_UNIT_PX, mTextHeight*3, dm);
        int shadowColor = WindowManagerService.getPropertyInt(tokens, 4,
                TypedValue.COMPLEX_UNIT_PX, 0xb0000000, dm);
        int color = WindowManagerService.getPropertyInt(tokens, 5,
                TypedValue.COMPLEX_UNIT_PX, 0x60ffffff, dm);
        int shadowRadius = WindowManagerService.getPropertyInt(tokens, 6,
                TypedValue.COMPLEX_UNIT_PX, 7, dm);
        int shadowDx = WindowManagerService.getPropertyInt(tokens, 8,
                TypedValue.COMPLEX_UNIT_PX, 0, dm);
        int shadowDy = WindowManagerService.getPropertyInt(tokens, 9,
                TypedValue.COMPLEX_UNIT_PX, 0, dm);
        // ...
    }
    // ...
}

由于水印的文件字是用16字制表示，不好直接写出来。下面提供一个简单的c代码用于生成我们所需要的水印配置文件：

$ cat > create_watermark.c << EOF

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

int main(int argc, char *argv[])
{
    char *msg = "Hello, world!";
    char *hex = "0123456789abcdef";
    int i;

    for (i = 0; i < strlen(msg); i++) {
        int ch = 255 - msg[i];
        printf("%c%c", hex[ch >> 4], hex[ch & 0xf]);
    }
    printf("%%%d", 40);
    return 0;
}
EOF

编译代码：

$ gcc -o create_watermark create_watermark.c

创建system/etc/setup.conf:

$ ./create_watermark > system/etc/setup.conf