从haskell调用C opencv函数 [英] Calling a C opencv function from haskell

问题描述

我试图使用OpenCV与Haskell。我的想法是从Haskell调用c ++函数。

现在我这样做：

  { - ＃LANGUAGE ForeignFunctionInterface＃ - } 
 
模块Lib 
（
 someFunc 
）其中
 
 import Foreign.C 
 import Foreign.C.String 
 import Foreign.C.Types 
 import Foreign.Ptr 
 
 data LplROI = LplROI {
 coi： ：CInt，
 xOffset :: CInt，
 yOffset :: CInt 
} 
 
 data LpImage = LpImage {
 align :: CInt，
 alphaChannel :: CInt，
 borderConst :: CInt，
 borderMode :: CInt，
 channelSeq :: CChar，
 colorModel :: CChar，
 dataOrder :: CInt ，
 depth :: CInt，
 height :: CInt，
 id :: CInt，
 imageData :: CChar，
 mageDataOrigin :: CChar，
 imageId :: CChar，
 imageSize :: CInt，
 maskROI :: LpImage，
 nChannels :: CInt，
 nSize :: CInt，
 origin :: CInt， 
 roi :: LplROI，
 tileInfo :: CChar，
 width :: CInt，
 widthStep :: CInt 
} 
 
 ccall_ZN2cv6imreadERKNS_6StringEiimRead_ImRead :: CString  - > CInt→> IO（Ptr LpImage）
 
 someFunc = do 
 filename<  -  newCString/home/chuck/Pictures/such-a-bad-day.jpg
 imRead_ImRead filename 1 
  

我阅读这篇文章来自Haskell的CPlusPlus ，因此我得到了名称​​ _ZN2cv6imreadERKNS_6StringEi 。

但是GHCi说：

ByteCodeLink：找不到标签
在交互式链接期间，GHCi找不到以下符号：
_ZN2cv6imreadERKNS_6StringEi

在Python中，我应该import cv2，但我不知道它如何在Haskell上工作。

a href =https://wiki.haskell.org/FFI_cook_book =nofollow> FFI厨师书但我不能得到我的问题的答案。

有什么想法吗？

解决方案

OpenCV api是用C ++编写的。这就是为什么调用它的方式在这里： haskell的C ++ 。但是当你在/ usr / lib /下安装OpenCV时，你不会得到一个.so文件，例如 cv2.so 。这意味着使用 foreign import ccall 很难使用c名称。
所以，我使用@ReidBarton说 haskell-opencv ，它很好地工作。或者至少比另一种方式更容易。

以下是使用示例：

 模块Lib 
（someFunc 
）其中
 
 import Control.Monad（void）
导入合格的OpenCV为CV 
导入合格的Data.ByteString为B 
 
 someFunc :: IO（）
 someFunc = do 
 img<  -  CV.imdecode CV.ImreadUnchanged< $> B.readFile/some_pic.jpg
 CV.withWindowtest$ \window  - > do 
 CV.imshow window img 
 void $ CV.waitKey 10000 
  

stack.yaml 我添加了这个：

 包：
  -  location：
 git：https://github.com/LumiGuide/haskell-opencv.git 
 commit：07afde39fa16f7a4282d4a812e70b9ed33d0f3ef 
  - '。'
  
 
 
 
因此看起来是cabal文件的一部分：
  library 
 hs-source-dirs：src 
 exposed-modules：Lib 
 build-depends：base> = 4.7& < 5 
，opencv 
，bytestring 
默认语言：Haskell2010 
 
可执行文件simple-exe 
 hs-source-dirs：app 
 main -is：Main.hs 
  -  ghc-options：-threaded -rtsopts -with-rtsopts = -N 
 build-depends：base 
，simple 
，opencv 
，bytestring 
默认语言：Haskell2010 
 
 test-suite simple-test 
 type：exitcode-stdio-1.0 
 hs-source-dirs：test 
 main-is：Spec.hs 
 build-depends：base 
，simple 
，opencv 
，bytestring 
  -  ghc-options：-threaded  - rtsopts -with-rtsopts = -N 
 default-language：Haskell2010 
  
有人。 
 
I'm trying to use OpenCV with Haskell. My idea is calling the c++ function from Haskell.

Right now I'm doing this: 
{-# LANGUAGE ForeignFunctionInterface #-}

module Lib
    (
        someFunc
    ) where

import Foreign.C
import Foreign.C.String
import Foreign.C.Types
import Foreign.Ptr

data LplROI = LplROI {
    coi :: CInt,
    xOffset :: CInt,
    yOffset :: CInt
}

data LpImage = LpImage {
    align :: CInt,
    alphaChannel :: CInt,
    borderConst :: CInt,
    borderMode :: CInt,
    channelSeq :: CChar,
    colorModel :: CChar,
    dataOrder :: CInt,
    depth :: CInt,
    height :: CInt,
    id :: CInt,
    imageData :: CChar, 
    mageDataOrigin :: CChar,
    imageId :: CChar,
    imageSize :: CInt,
    maskROI :: LpImage,
    nChannels :: CInt, 
    nSize :: CInt,
    origin :: CInt,
    roi :: LplROI,
    tileInfo :: CChar,
    width :: CInt,
    widthStep :: CInt
}

foreign import ccall "_ZN2cv6imreadERKNS_6StringEi" imRead_ImRead :: CString -> CInt -> IO (Ptr LpImage)

someFunc = do
    filename <- newCString "/home/chuck/Pictures/such-a-bad-day.jpg"
    imRead_ImRead filename 1
I read this post CPlusPlus from Haskell, and so I got the name _ZN2cv6imreadERKNS_6StringEi. In 2.1.1 Finding the mangled named.

But GHCi says: 

  
ByteCodeLink: can't find label
  During interactive linking, GHCi couldn't find the following symbol:
    _ZN2cv6imreadERKNS_6StringEi
In Python I should "import cv2", but I don't know how it works on Haskell.

I also read: FFI cook book But I can't get an answer to my question there.

Any idea?
解决方案
What I was trying doesn't work. 
The OpenCV api is written in C++. That's why the way to call it is here: C++ from haskell. But when you install OpenCV in "/usr/lib/", you don't get a .so file like cv2.so. It means that's quite difficult to use foreign import ccall as the c-name is not built. 
So, I used what @ReidBarton said "haskell-opencv" and it works nicely. Or at least easier than the other way. 

Here is a use example:
module Lib
( someFunc
) where

import Control.Monad ( void )
import qualified OpenCV as CV
import qualified Data.ByteString as B

someFunc :: IO ()
someFunc = do
    img <- CV.imdecode CV.ImreadUnchanged <$> B.readFile "/some_pic.jpg"
    CV.withWindow "test" $ \window -> do
     CV.imshow window img
     void $ CV.waitKey 10000
in the stack.yaml I added this:
packages:    
 - location:
    git: https://github.com/LumiGuide/haskell-opencv.git
    commit: 07afde39fa16f7a4282d4a812e70b9ed33d0f3ef
 - '.'
and so looks a part of the cabal file:
library  
 hs-source-dirs:      src
  exposed-modules:     Lib
  build-depends:       base >= 4.7 && < 5
                     , opencv
                     , bytestring
  default-language:    Haskell2010

 executable simple-exe
  hs-source-dirs:      app
  main-is:             Main.hs
 -- ghc-options:         -threaded -rtsopts -with-rtsopts=-N
  build-depends:       base
                     , simple
                     , opencv
                     , bytestring
  default-language:    Haskell2010

 test-suite simple-test
  type:                exitcode-stdio-1.0
  hs-source-dirs:      test
  main-is:             Spec.hs
  build-depends:       base
                     , simple
                     , opencv
                     , bytestring
 -- ghc-options:         -threaded -rtsopts -with-rtsopts=-N
  default-language:    Haskell2010
I hope it helps someone. 

                        
这篇关于从haskell调用C opencv函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！