rv1126 opencv c++加中文水印

1背景

Ubuntu 18.04 PC上用opencv c++加中文水印可以成功，通过libopencv_freetype.so，但是rv1126上没有这个库，网上发现opencv本身不带freetype，需要opencv_contrib扩展，里面有modules带freetype，所以需要移植开源的opencv_contrib，并将配置项对接到menuconfig里面。

开源链接如下：

https://github.com/opencv/opencv_contrib

或者

https://github.com/Itseez/opencv_contrib

解决办法：在buildroot里面看到一段注释如下：opencv3.mk里面

所以解决方法是将freetype模块从opencv_contrib里面移到了opencv里面，然后加上编译选项，修改opencv3.mk来编译freetype，需要注意的是，opencv里面的freetype，需要依赖系统的两个工具：

BR2_PACKAGE_FREETYPE
BR2_PACKAGE_HARFBUZZ

2.步骤

1.将freetype模块从opencv_contrib里面拷贝到opencv的module里面，也就是解压buildroot/dl目录下opencv的压缩包，然后将freetype源码拷贝到解压的opencv源码目录中module文件夹下，拷贝之后重新打包成tar.gz，buildroot会在编译的时候自动解压的。

2.修改buildroot/package/opencv3里面的配置：

zl@zl-Lenovo:~/rv1126-workspace/rv1126_rv1109_linux_sdk/buildroot/package/opencv3$ git diff .
diff --git a/package/opencv3/Config.in b/package/opencv3/Config.in
index b9ea033f13..a54cc4249b 100644
--- a/package/opencv3/Config.in
+++ b/package/opencv3/Config.in
@@ -176,6 +176,14 @@ config BR2_PACKAGE_OPENCV3_LIB_SHAPE
          Include opencv_shape (shape descriptors and matchers) module
          into the OpenCV build.

+config BR2_PACKAGE_OPENCV3_LIB_FREETYPE
+        bool "freetype"
+        depends on BR2_PACKAGE_FREETYPE
+        depends on BR2_PACKAGE_HARFBUZZ
+        help
+          Include opencv_freetype module into the OpenCV build. This
+         FreeType2 wrapper module allows to draw strings with outlines and bitmaps.
+
 config BR2_PACKAGE_OPENCV3_LIB_STITCHING
        bool "stitching"
        select BR2_PACKAGE_OPENCV3_LIB_CALIB3D
diff --git a/package/opencv3/opencv3.mk b/package/opencv3/opencv3.mk
index 3e3e5987a5..cc0769c894 100644
--- a/package/opencv3/opencv3.mk
+++ b/package/opencv3/opencv3.mk
@@ -104,6 +104,7 @@ OPENCV3_CONF_OPTS += \
        -DBUILD_opencv_video=$(if $(BR2_PACKAGE_OPENCV3_LIB_VIDEO),ON,OFF) \
        -DBUILD_opencv_videoio=$(if $(BR2_PACKAGE_OPENCV3_LIB_VIDEOIO),ON,OFF) \
        -DBUILD_opencv_videostab=$(if $(BR2_PACKAGE_OPENCV3_LIB_VIDEOSTAB),ON,OFF) \
+       -DBUILD_opencv_freetype=$(if $(BR2_PACKAGE_OPENCV3_LIB_FREETYPE),ON,OFF) \
        -DBUILD_opencv_viz=OFF \
        -DBUILD_opencv_world=OFF

3.make menuconfig配置相应的项

从上面修改可以看到opencv的freetype模块，依赖系统的两个模块：

BR2_PACKAGE_FREETYPE和BR2_PACKAGE_HARFBUZZ

需要确保这两个是打开的，opencv3里面才会出现相应的freetype选项，勾选之后，保存配置修改，然后删掉opencv3，重新编译就可以生成libopencv_freetype.so了。注意：如果是pc上编译的话，需要更新下交叉编译链。里面的库变了。

结论：通过测试上面修改之后，通过下面的代码，可以给图片添加中文水印：

const char *filename = "../ttf-test/opencv-test.jpg";
cv::Mat mat = cv::imread(filename);
if (mat.empty())
{
    throw("Faild open file.");
}

cv::Point p = cv::Point(mat.cols/2, mat.rows/2);
cv::Ptr<cv::freetype::FreeType2> ft2 = cv::freetype::createFreeType2();
// cv::String ttf_path = "FZHuangTJXSJF.TTF";
// cv::String ttf_path = "simfang.ttf";
cv::String ttf_path = "../ttf-test/simsun.ttf";
ft2->loadFontData(ttf_path,0);
ft2->putText(mat, "勿忘初心", p, 70, cv::Scalar(0, 255, 0), cv::FILLED,cv::LINE_AA,true);

cv::imwrite("../ttf-test/opencv-test-new.jpg", mat);
// 保存修改后的图片

注意：

实际使用中发现，freetype的这种方式，调用ft2->putText的时候，mat必须是3通道的，否则会报错，原因如下图所示：