Hello OpenCV on iOS

[soapgu]

• 前言

上一篇已经成功在本机mac上安装opcv的库，并启动一个C++控制台程序成功调用。
但是一般我们的程序都是以app的形式作为载体的，我们需要能直接调用api并且和当前应用的界面有个“深度对接”。本来是想先从mac App，AppKit这条路来尝试的。但是opencv官网上貌似暂时只支持ios平台。所以还是先走通ios这条路再尝试mac app，毕竟ios app 和mac app有很多相似点，实在不行可以考虑通用app在macOS直接运行

• 获取 opencv iOS的库之路

本来以为很“简单”，摸着邓兄过河就行了。

参考资料

• swift-使用opencv

1. 直接下载Libragy Realse - iOS pack
   从官方下载iOS的库，解压zip。opencv2.framework 加入到Framworks里面，在代码里面import opencv2，敲代码也没问题。但是build以后，报错了...

/Users/guhui/WorkSpace/PlayPen/OpenCVIOS/OpenCVIOS/ViewController.swift:9:8: Could not find module 'opencv2' for target 'arm64-apple-ios-simulator'; found: x86_64-apple-ios-simulator, armv7s, armv7s-apple-ios, armv7-apple-ios, i386-apple-ios-simulator, arm64-apple-ios, armv7, at: /Users/guhui/WorkSpace/PlayPen/OpenCVIOS/opencv2.framework/Modules/opencv2.swiftmodule

一下子有点懵，剧情不是按照我想的发展啊。
难道又是我M1 arm的锅，换个思路。我直接从源代码编译出来用总行吧。“一条龙服务”总不会不支持吧

2. build framwrok by source
   https://github.com/opencv/opencv/tree/4.x/platforms/ios/readme.txt 里面讲得还是蛮清楚的

进控制台

git clone [email protected]:opencv/opencv.git
python opencv/platforms/ios/build_framework.py ios

接下来是漫长的等待...
建议可以出去喝一杯再回来看
编译似乎没什么问题

重新引用opencv2.framework ，结果还是一样的报错

生成的sample项目编译一下也是一样的错误

3. 最终解决方案
   一下陷入迷茫不知道怎么解决了。
   
   还是要冷静，首先从报错关键信息入手应该是arm64-apple-ios-simulator这个关键字，打开opencv2.framework，从/Modules/opencv2.swiftmodule看确实没有arm64-apple-ios-simulator，只有“兄弟” i386-apple-ios-simulator，x86_64-apple-ios-simulator。根本就没有编译出这个架构的模块
   那再回头到编译这个动作去解决

openCV 官方教程对编译库有更详细的说明

• Installation in iOS
  里面提到了--iphonesimulator_archs可以改架构

输入help命令看看详细说明

guhui@guhuideMacBook-Pro Githubs % python opencv/platforms/ios/build_framework.py ios --help                                                            
usage: build_framework.py [-h] [--opencv DIR] [--contrib DIR]
                          [--without MODULE] [--disable FEATURE] [--dynamic]
                          [--disable-bitcode]
                          [--iphoneos_deployment_target IPHONEOS_DEPLOYMENT_TARGET]
                          [--build_only_specified_archs]
                          [--iphoneos_archs IPHONEOS_ARCHS]
                          [--iphonesimulator_archs IPHONESIMULATOR_ARCHS]
                          [--enable_nonfree] [--debug] [--debug_info]
                          [--framework_name FRAMEWORK_NAME] [--legacy_build]
                          [--run_tests] [--build_docs] [--disable-swift]
                          OUTDIR

The script builds OpenCV.framework for iOS.

positional arguments:
  OUTDIR                folder to put built framework

optional arguments:
  -h, --help            show this help message and exit
  --opencv DIR          folder with opencv repository (default is "../.."
                        relative to script location)
  --contrib DIR         folder with opencv_contrib repository (default is
                        "None" - build only main framework)
  --without MODULE      OpenCV modules to exclude from the framework. To
                        exclude multiple, specify this flag again, e.g. "--
                        without video --without objc"
  --disable FEATURE     OpenCV features to disable (add WITH_*=OFF). To
                        disable multiple, specify this flag again, e.g. "--
                        disable tbb --disable openmp"
  --dynamic             build dynamic framework (default is "False" - builds
                        static framework)
  --disable-bitcode     disable bitcode (enabled by default)
  --iphoneos_deployment_target IPHONEOS_DEPLOYMENT_TARGET
                        specify IPHONEOS_DEPLOYMENT_TARGET
  --build_only_specified_archs
                        if enabled, only directly specified archs are built
                        and defaults are ignored
  --iphoneos_archs IPHONEOS_ARCHS
                        select iPhoneOS target ARCHS. Default is
                        "armv7,armv7s,arm64"
  --iphonesimulator_archs IPHONESIMULATOR_ARCHS
                        select iPhoneSimulator target ARCHS. Default is
                        "i386,x86_64"
  --enable_nonfree      enable non-free modules (disabled by default)
  --debug               Build "Debug" binaries (disabled by default)
  --debug_info          Build with debug information (useful for Release mode:
                        BUILD_WITH_DEBUG_INFO=ON)
  --framework_name FRAMEWORK_NAME
                        Name of OpenCV framework (default: opencv2, will
                        change to OpenCV in future version)
  --legacy_build        Build legacy opencv2 framework (default: False,
                        equivalent to "--framework_name=opencv2
                        --without=objc")
  --run_tests           Run tests
  --build_docs          Build docs
  --disable-swift       Disable building of Swift extensions

IPHONESIMULATOR_ARCHS select iPhoneSimulator target ARCHS. Default is "i386,x86_64"
文档很清晰，默认架构没有。
尝试

python opencv/platforms/ios/build_framework.py ios --iphonesimulator_archs arm64 

Using IPHONEOS_DEPLOYMENT_TARGET=9.0
Using iPhoneOS ARCHS=[u'armv7', u'armv7s', u'arm64']
Using iPhoneSimulator ARCHS=[u'arm64']
============================================================
ERROR: Cannot have the same architecture for multiple platforms in a fat framework! Consider using build_xcframework.py in the apple platform folder instead. Duplicate archs are set([u'arm64'])
============================================================

晕死，模拟器和iphone架构重复还不给执行。
不高兴去改脚本了，暂时把arm64从iphone架构阉掉，反正我先只用模拟器运行

 python opencv/platforms/ios/build_framework.py ios --iphonesimulator_archs x86_64,arm64 --iphoneos_archs armv7,armv7s

• Demo Code

storyboard拖一个button并和ViewController关联
从unsplash下一个图拖到Assets里面

//
//  ViewController.swift
//  OpenCVIOS
//
//  Created by guhui on 2021/12/29.
//

import UIKit
import opencv2

class ViewController: UIViewController {
    @IBOutlet var imageButton: UIButton!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        let orgImage = UIImage(named: "picture")
        let src = Mat(uiImage: orgImage!)
        let gray = Mat()
        Imgproc.cvtColor(src: src, dst: gray, code: .COLOR_RGBA2GRAY)
        imageButton.setImage(gray.toUIImage(), for: .normal)
    }

}

运行结果