Camera Hal3实现水印或者弹幕功能

1，水印或者弹幕实现的效果图

2，因为Camera Hal3中图像的格式yuv420sp格式，那么水印或者弹幕就需要转换成yuv420sp的格式，这样才能将水印或者弹幕的图像合成到camera的每一帧图像中。水印或者弹幕的图像这里提供的是32×24 bmp格式的图像，如图：

这个提供水印图像主要是数组和字母，空格，冒号，斜线和部分汉字。
水印或者弹幕图像的下载路径：https://download.csdn.net/download/jiangchaobing_2017/88540699

3，下面就是通过fopen和fread函数去打开读取水印bmp格式的图像

int WaterMark::InitwWaterMark()
{
    FILE *fp = NULL;
    int i;
    int pic_width = 0, pic_height = 0;
    char filename[256];
    unsigned char *argb_buf = NULL;


    for(i = 0; i < MAX_ICON_NUM; i++) {
        sprintf(filename, "%s/argb8888_24x32_%d.bmp", WATERMARK_BMP_DIR, i);
        ALOGE("open file %s\n", filename);
        fp = fopen(filename, "r");
        if(NULL == fp) {
            ALOGE("Fail to open file %s(%s)!", filename, strerror(errno));
            goto OPEN_FILE_ERR;
        }
        icon_arry[i].id = i;

        fseek(fp, 18, SEEK_SET);
        fread(&pic_width, 1, 4, fp);
        fread(&pic_height, 1, 4, fp);
        icon_arry[i].width = abs(pic_width);
        icon_arry[i].height = abs(pic_height);
        ALOGE("real width=%d(%d), height=%d(%d)\n", icon_arry[i].width, pic_width, icon_arry[i].height, pic_height);

        icon_arry[i].y = (unsigned char*)malloc(icon_arry[i].width * icon_arry[i].height*5/2);
        if(NULL == icon_arry[i].y) {
            ALOGE("malloc picture yuv fail !\n");
            fclose(fp);
            goto ALLOC_Y_ERR;
        }
        memset(icon_arry[i].y, 0xff, (icon_arry[i].width * icon_arry[i].height*5/2));
        icon_arry[i].alph = icon_arry[i].y + icon_arry[i].width * icon_arry[i].height;
        icon_arry[i].c = icon_arry[i].alph + icon_arry[i].width * icon_arry[i].height;

        argb_buf = (unsigned char *)malloc(icon_arry[i].width * icon_arry[i].height * 4);
        if (NULL == argb_buf) {
            ALOGE("malloc bmp buf fail !\n");
            fclose(fp);
            goto ALLOC_BUF_ERR;
        }

        fseek(fp, 54, SEEK_SET);
        fread(argb_buf, icon_arry[i].width * icon_arry[i].height * 4, 1, fp);

        ARGB8888ToYUV420sp(argb_buf, icon_arry[i].width, icon_arry[i].height,
                   icon_arry[i].y, icon_arry[i].c, icon_arry[i].alph);

        fclose(fp);
        free(argb_buf);
    }

    return 0;

ALLOC_BUF_ERR:
ALLOC_Y_ERR:
OPEN_FILE_ERR:

    for(i = 0; i < MAX_ICON_NUM; ++i) {
        if(icon_arry[i].y != NULL) {
            free(icon_arry[i].y);
            icon_arry[i].y = NULL;
        }
    }
    return -1;
}

而这里ARGB8888ToYUV420sp主要是将bmp格式解析处理的图像数据转换成yuv420sp格式。rgb转yuv的换算公式：

4，将水印转换的yuv格式图像和camera的图像进行合成成一帧图像

void WaterMark::Yuv420spBlending(unsigned char *bg_y, unsigned char *bg_c, int bg_width, int bg_height, 
						int left, unsigned int top, int fg_width, int fg_height,
                        unsigned char *fg_y, unsigned char *fg_c, unsigned char *alph)
{
    unsigned char *bg_y_p = NULL;
    unsigned char *bg_c_p = NULL;
    int i = 0;
    int j = 0;

    bg_y_p = bg_y + top * bg_width + left;
    bg_c_p = bg_c + (top >>1)*bg_width + left;

    for(i = 0; i<(int)fg_height; i++) {
        if((i&1) == 0) {
            for(j=0; j< (int)fg_width; j++) {
                *bg_y_p = ((256 - *alph)*(*bg_y_p) + (*fg_y++)*(*alph))>>8;
                *bg_c_p = ((256 - *alph)*(*bg_c_p) + (*fg_c++)*(*alph))>>8;

                alph++;
                bg_y_p++;
                bg_c_p++;
            }
            bg_c_p = bg_c_p + bg_width - fg_width;
        } else {
            for(j=0; j< (int)fg_width; j++) {
                *bg_y_p = ((256 - *alph)*(*bg_y_p) + (*fg_y++)*(*alph))>>8;
                alph++;
                bg_y_p++;
            }
        }
            bg_y_p = bg_y_p + bg_width - fg_width;
    }
}