Saving GDI32.dll bitmap to disk in Golang

Question

My first SO question :-) I wish to take a screenshot from Golang by calling into User32.dll and GDI32.dll on a windows machine (project requirement).

I have a handle to the bitmap containing screenshot pixels. However, I don't know how to access its data or how to save it to disk. Anyone know how to map GDI bitmap to Golang []byte and then save as a JPG or PNG?

package main
import "syscall"

var (
    user32            = syscall.NewLazyDLL("user32.dll")
    procGetClientRect = user32.NewProc("GetClientRect")
    // etc...
    gdi32             = syscall.NewLazyDLL("gdi32.dll")
    procCreateDC      = gdi32.NewProc("CreateDC")
    SRCCOPY      uint = 13369376
   //etc...
)

//
// omitted for brevity
//
func TakeDesktopScreenshotViaWinAPI() {

    // these are all calls to user32.dll or gdi32.dll
    hDesktop := GetDesktopWindow()
    desktopRect := GetClientRect(hDesktop)
    width := int(desktopRect.Right - desktopRect.Left)
    height := int(desktopRect.Bottom - desktopRect.Top)

    // create device contexts
    srcDC := GetDC(hDesktop)
    targetDC := CreateCompatibleDC(srcDC)

    // create bitmap to copy to
    hBitmap := CreateCompatibleBitmap(targetDC, width, height)

    // select the bitmap into target DC
    hOldSelection := SelectObject(targetDC, HGDIOBJ(hBitmap))

    //bit block transfer from src to target
    BitBlt(targetDC, 0, 0, width, height, srcDC, 0, 0, SRCCOPY)

   // how to save the  the data in
   // *hBitmap ???

   // restore selection
   SelectObject(targetDC, hOldSelection)

   // clean up
   DeleteDC(HDC(targetDC))
   ReleaseDC(hDesktop, srcDC)
   DeleteObject(HGDIOBJ(hBitmap))
}

Answer 1

You could just use the screenshot library by vova616, or take a look at the screenshot_windows.go for the required conversion method.

As per the provided example:

package main

import (
    "github.com/vova616/screenshot"
    "image/png"
    "os"
)

func main() {
    img, err := screenshot.CaptureScreen()
    if err != nil {
        panic(err)
    }
    f, err := os.Create("./ss.png")
    if err != nil {
        panic(err)
    }
    err = png.Encode(f, img)
    if err != nil {
        panic(err)
    }
    f.Close()
}