NDK处理图片——添加文字和图片水印

        马化腾说过腾讯的服务器一天存储几个亿的图片，可见图片已经成为移动社交必不可少的元素。而用户往往喜欢在原图基础上编辑文字或者添加配图，达到图文并茂、生动形象的目的，以表达此时此地此景此物。添加水印已成为美图秀秀、QQ天天P图、各大直播平台的必备技能。接下来给大家介绍下，这是基于android移动端的NDK处理图片，添加文字或者图片水印。

        先看下添加水印后的效果：

        一张图片是由宽x高的二维矩阵像素点构成的，添加水印就是将覆盖层的矩阵像素与原图矩阵像素叠加。而一个像素是由ARGB（Alpha、Red、Green、Blue）组成，像素叠加需要拆分成ARGB分量进行叠加。native层处理代码如下：

jintArrayJava_com_frank_image_ImageUtil_textWaterMark(JNIEnv *env, jobject, jintArray pixels, jint width, jint height,                                         jintArray textPixels, jint textWidth, jint textHeight){    //像素数组拷贝到native层    jint *pixel = env->GetIntArrayElements(pixels, false);    jint *textPixel = env->GetIntArrayElements(textPixels, false);    int size = width * height;    int alpha, red, green, blue;    int text_alpha, text_red, text_green, text_blue;    int x, y;    for(x=0; x<width; x++){        for(y=0; y< height; y++){            //获取每一个像素点            int color = pixel[y*width + x];            alpha = (color >> 24) & 0xFF;            red = (color >> 16) & 0xFF;            green = (color >> 8) & 0xFF;            blue = color & 0xFF;            //获取text的像素点,与原图像素相加            if(x < textWidth && y < textHeight){                int textColor = textPixel[y*textWidth + x];                text_alpha = (textColor >> 24) & 0xFF;                text_red = (textColor >> 16) & 0xFF;                text_green = (textColor >> 8) & 0xFF;                text_blue = textColor & 0xFF;                //新的RGB分量=图片分量(R/G/B) + 文本分量(R/G/B)                red   = (1-text_alpha)*red  + text_alpha*text_red;                green = (1-text_alpha)*green + text_alpha*text_green;                blue  = (1-text_alpha)*blue + text_alpha*text_blue;                //边界检测:0<rgb<255                red = red > 255 ? 255 : (red < 0 ? 0 : red);                green = green > 255 ? 255 : (green < 0 ? 0 : green);                blue = blue > 255 ? 255 : (blue < 0 ? 0 : blue);            }            //重新赋值给每个像素点            pixel[y*width + x] = (alpha << 24) | (red << 16) | (green << 8) | blue;        }    }    jintArray newPixel = env->NewIntArray(size);    env->SetIntArrayRegion(newPixel, 0, size, pixel);    env->ReleaseIntArrayElements(pixels, pixel, 0);    env->ReleaseIntArrayElements(textPixels, textPixel, 0);    return newPixel;}

        java层调用native层的文字水印处理方法，传入原图像素数组、原图宽度、原图高度、水印的像素数组、水印宽度、水印高度等参数。等待native层处理完成返回新数组，然后根据新数组创建新的Bitmap：

    /**     * 使用NDK向图片添加文字水印     * @param drawable drawable     * @param imageView imageView     * @param text 文本内容     */    private void textWaterMark(Drawable drawable, ImageView imageView, String text){        if (drawable != null && drawable instanceof BitmapDrawable) {            Bitmap bitmap = ((BitmapDrawable)drawable).getBitmap();            int width = bitmap.getWidth();            int height = bitmap.getHeight();            int[] pixels = new int[width * height];            //获取bitmap的所有pixel像素点            bitmap.getPixels(pixels, 0, width, 0, 0, width, height);            //文本转成bitmap,再获取像素数组            Bitmap textBitmap = BitmapUtil.textToBitmap(text, Color.BLUE, 16, this);            int textWidth = textBitmap.getWidth();            int textHeight = textBitmap.getHeight();            int[] textPixel = new int[textWidth * textHeight];            textBitmap.getPixels(textPixel, 0, textWidth, 0, 0, textWidth, textHeight);            //ndk处理像素点数组            int[] newPixels = ImageUtil.textWaterMark(pixels, width, height, textPixel, textWidth, textHeight);            Bitmap ndkBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);            //重新设置bitmap的所有pixel像素点            ndkBitmap.setPixels(newPixels, 0, width, 0, 0, width, height);            imageView.setImageBitmap(ndkBitmap);        }    }

        除此之外，需要加载so库，声明native方法供java调用：

    static {        System.loadLibrary("image");    }    public static native int[] textWaterMark(int[] pixels, int width, int height,                                         int[] textPixels, int textWidth, int textHeight);

        这样看起来，只是在原图左上角添加水印，不够灵活。那么问题来了，有没办法去灵活控制水印在原图的位置呢？答案是肯定的，只需要传入x、y坐标的偏移量，native层加上偏移量处理就可以了。代码如下：

jintArrayJava_com_frank_image_ImageUtil_textWaterMark(JNIEnv *env, jobject, jintArray pixels, jint width, jint height,                                         jintArray textPixels, jint textWidth, jint textHeight,                                         jint offsetX, jint offsetY){    //像素数组拷贝到native层    jint *pixel = env->GetIntArrayElements(pixels, false);    jint *textPixel = env->GetIntArrayElements(textPixels, false);    int size = width * height;    int alpha, red, green, blue;    int text_alpha, text_red, text_green, text_blue;    int x, y;    for(x=0; x<width; x++){        for(y=0; y< height; y++){            //获取每一个像素点            int color = pixel[y*width + x];            alpha = (color >> 24) & 0xFF;            red = (color >> 16) & 0xFF;            green = (color >> 8) & 0xFF;            blue = color & 0xFF;            //获取text的像素点,与原图像素相加(加上偏移量判断，控制水印显示位置)            if(x > offsetX && x < (textWidth+offsetX) && y > offsetY && y < (textHeight+offsetY)){                int textColor = textPixel[(y-offsetY)*textWidth + (x-offsetX)];                text_alpha = (textColor >> 24) & 0xFF;                text_red = (textColor >> 16) & 0xFF;                text_green = (textColor >> 8) & 0xFF;                text_blue = textColor & 0xFF;                //新的RGB分量=图片分量(R/G/B) + 文本分量(R/G/B)                red   = (1-text_alpha)*red  + text_alpha*text_red;                green = (1-text_alpha)*green + text_alpha*text_green;                blue  = (1-text_alpha)*blue + text_alpha*text_blue;                //边界检测:0<rgb<255                red = red > 255 ? 255 : (red < 0 ? 0 : red);                green = green > 255 ? 255 : (green < 0 ? 0 : green);                blue = blue > 255 ? 255 : (blue < 0 ? 0 : blue);            }            //重新赋值给每个像素点            pixel[y*width + x] = (alpha << 24) | (red << 16) | (green << 8) | blue;        }    }    jintArray newPixel = env->NewIntArray(size);    env->SetIntArrayRegion(newPixel, 0, size, pixel);    env->ReleaseIntArrayElements(pixels, pixel, 0);    env->ReleaseIntArrayElements(textPixels, textPixel, 0);    return newPixel;}

        同样地，添加图片水印的native方法如下：

jintArrayJava_com_frank_image_ImageUtil_picWaterMark(JNIEnv *env, jobject, jintArray pixels, jint width, jint height,                                            jintArray overlayPixels, jint overlayWidth, jint overlayHeight,                                             jint offsetX, jint offsetY){    //像素数组拷贝到native层    jint *pixel = env->GetIntArrayElements(pixels, false);    jint *overlayPixel = env->GetIntArrayElements(overlayPixels, false);    int size = width * height;    int alpha, red, green, blue;    int x, y;    for(x=0; x<width; x++){        for(y=0; y< height; y++){            //获取每一个像素点            int color = pixel[y*width + x];            alpha = (color >> 24) & 0xFF;            red = (color >> 16) & 0xFF;            green = (color >> 8) & 0xFF;            blue = color & 0xFF;            //获取覆盖层图片的像素点            if(x > offsetX && x < (overlayWidth+offsetX) && y > offsetY && y < (overlayHeight+offsetY)){                int addColor = overlayPixel[(y-offsetY)*overlayWidth + (x-offsetX)];                //替换原图像素的RGBA                alpha = (addColor >> 24) & 0xFF;                red = (addColor >> 16) & 0xFF;                green = (addColor >> 8) & 0xFF;                blue = addColor & 0xFF;            }            //重新赋值给每个像素点            pixel[y*width + x] = (alpha << 24) | (red << 16) | (green << 8) | blue;        }    }    jintArray newPixel = env->NewIntArray(size);    env->SetIntArrayRegion(newPixel, 0, size, pixel);    env->ReleaseIntArrayElements(pixels, pixel, 0);    env->ReleaseIntArrayElements(overlayPixels, overlayPixel, 0);    return newPixel;}

        加上x、y坐标偏移量的添加水印效果如下：

        欢迎各位图片处理、多媒体开发爱好者相互交流，相互学习。。。