Screen capture in Haskell?

The Approach Tikhon mentioned is correct. Just to add some code to the answer he gave above

import Graphics.Win32.Windowimport Graphics.Win32.GDI.Bitmapimport Graphics.Win32.GDI.HDCimport Graphics.Win32.GDI.Graphics2Dmain = do desktop   <- getDesktopWindow -- Grab the Hwnd of the desktop, GetDC 0, GetDC NULL etc all work too          hdc       <- getWindowDC (Just desktop) -- Get the dc handle of the desktop          (x,y,r,b) <- getWindowRect desktop -- Find the size of the desktop so we can know which size the destination bitmap should be                                             -- (left, top, right, bottom)          newDC     <- createCompatibleDC (Just hdc) -- Create a new DC to hold the copied image. It should be compatible with the source DC          let width  = r - x -- Calculate the width          let height = b - y -- Calculate the Height          newBmp    <- createCompatibleBitmap hdc width height -- Create a new Bitmap which is compatible with the newly created DC          selBmp    <- selectBitmap newDC newBmp -- Select the Bitmap into the DC, drawing on the DC now draws on the bitmap as well          bitBlt newDC 0 0 width height hdc 0 0 sRCCOPY -- use SRCCOPY to copy the desktop DC into the newDC          createBMPFile "Foo.bmp" newBmp newDC  -- Write out the new Bitmap file to Foo.bmp          putStrLn "Bitmap image copied" -- Some debug message          deleteBitmap selBmp -- Cleanup the selected bitmap          deleteBitmap newBmp -- Cleanup the new bitmap          deleteDC newDC      -- Cleanup the DC we created.

This was just quickly put together, but it saves a screenshot of to a file named Foo.bmp. Ps. To whomever wrote the Win32 Library, nicely done :)

You can also do it in a cross-platform way with GTK.

That would not be much different from doing it with C: Taking a screenshot with C/GTK.

{-# LANGUAGE OverloadedStrings #-}import Graphics.UI.Gtkimport System.Environmentimport Data.Text as Tmain :: IO ()main = do    [fileName] <- getArgs    _ <- initGUI    Just screen <- screenGetDefault    window <- screenGetRootWindow screen    size <- drawableGetSize window    origin <- drawWindowGetOrigin window    Just pxbuf <-        pixbufGetFromDrawable            window            ((uncurry . uncurry Rectangle) origin size)    pixbufSave pxbuf fileName "png" ([] :: [(T.Text, T.Text)])

You should be able to do this with the Win32 API. Based on What is the best way to take screenshots of a Window with C++ in Windows?, you need to get the context of the window and then copy the image from it using GetWindowDC and BitBlt respectively.

Looking around the Haskell Win32 API documentation, there is a getWindowDC function in Graphics.Win32.Window. This returns an IO HDC. There is a bitblt function in Graphics.Win32.GDI.Graphics2D. This function takes an HDC along with a bunch of INTs which presumably correspond to the arguments it takes in C++.

Unfortunately, I don't have a Windows machine handy, so I can't write the actual code. You'll have to figure out how to use the Win32 API functions yourself, which might be a bit of a bother.

When you do, it would be great if you factored it into a library and put it up on Hackage--Windows does not usually get much love in Haskell land (as I myself show :P), so I'm sure other Windows programmers would be grateful for an easy way to take screenshots.