在SWIG的外部库中引用特定类 [英] Referencing specific classes in an external library with SWIG

问题描述

目前，我试图包装我的自定义C ++库以供Java（最终Android）使用。我的库使用OpenCV Mat 和 Size 类作为输入。下面是我迄今为止的一个示例SWIG界面：

Currently, I'm trying to wrap my custom C++ library for use in Java (and ultimately Android). My library uses the OpenCV Mat and Size classes as input. Below, is an example SWIG interface of what I have so far:

%module customLib

%include <std_vector.i>
%include <std_string.i>

%{
#include "opencv2/core/core.hpp"
#include "../include/myinc/CustomLib.h"
%}

namespace cv {
    class Mat {};
    class Size {};
}

namespace myinc {
    CustomType preprocessMatrix(const cv::Mat& src, cv::Mat& dst, const cv::Size& ksize);
}

OpenCV有 Mat 和 Size 已经;我想知道我在这里做了什么会导致命名冲突一旦我添加OpenCV自己的Java框架。这是通过SWIG包括对外部库类的引用的正确方法吗？

OpenCV has Java wrappers for Mat and Size already; I'm wondering if what I've done here will cause naming conflicts once I add OpenCV's own Java framework. Is this the correct way to include references to an external library's classes via SWIG? Or, is there a better way to accomplish this type of thing?

推荐答案

我想到了这一切！我花了一些时间来理解SWIG的Java类型打印系统是如何工作的（大多数示例都会覆盖一些重要的概念）。

I figured this one out finally! It took me a bit to understand how SWIG's Java typemapping system worked (most of the examples gloss over some of the important concepts).

如果其他人无法理解如何编写Java类型的图形，这里是一种帮助我的方法。我决定最容易从自上而下的角度（即Java - >中间JNI - > JNI）查看类型映射。首先，将 jstype 定义为要在Java类中查看的类型（例如module_name.java）。使用 javain 告诉SWIG如何将您的变量从Java类传递到中间JNI类（例如module_nameJNI.java）。接下来，将 jtype 定义为与 javain 相同的类型。例如， $ javainput.getNativeObjectAddr（）返回 long ，因此这将成为我的 jtype 。最后，定义 jni 作为实际的JNI函数将使用什么。

If others are having trouble understanding how to write Java typemaps, here is a way that helped me. I decided it was easiest to view the typemaps from a top-down perspective (i.e., Java -> intermediate JNI -> JNI). First, define the jstype as the type you want to see in your Java classes (e.g., module_name.java). Use javain to tell SWIG how to pass your the variable from the Java class to the intermediate JNI class (e.g., module_nameJNI.java). Next, define the jtype as the same type as javain would be. For example, $javainput.getNativeObjectAddr() returns a long, so this would become my jtype. Finally, define jni as what the actual JNI function will be using.

下面是我在OpenCV的Java界面（2.4.5版）上运行的SWIG类型图：

Below, are the SWIG typemaps I came up with for running on top of OpenCV's Java interface (as of 2.4.5):

    %typemap(jstype) cv::Mat& "org.opencv.core.Mat"
    %typemap(javain) cv::Mat& "$javainput.getNativeObjAddr()"
    %typemap(jtype) cv::Mat& "long"
    %typemap(jni) cv::Mat& "jlong"

    %typemap(in) cv::Mat& {
            $1 = *(cv::Mat **)&$input;
    }

    %typemap(jstype) cv::Size& "org.opencv.core.Size"
    %typemap(javain) cv::Size& "$javainput"
    %typemap(jtype) cv::Size& "org.opencv.core.Size"
    %typemap(jni) cv::Size& "jobject"

    %typemap(in) cv::Size& {
            jclass sizeClass = JCALL1(GetObjectClass, jenv, $input);
            jfieldID widthFieldId = JCALL3(GetFieldID, jenv, sizeClass, "width", "D");
            jfieldID heightFieldId = JCALL3(GetFieldID, jenv, sizeClass, "height", "D");
            double width = JCALL2(GetDoubleField, jenv, $input, widthFieldId);
            double height = JCALL2(GetDoubleField, jenv, $input, heightFieldId);
            $1 = new cv::Size((int)width, (int)height);
    }

    %typemap(freearg) cv::Size& {
            delete $1;
    }

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