screenshot.go

package main

import (
	"fmt"
	"syscall"
	"unsafe"
)

var (
	user32                 = syscall.NewLazyDLL("user32.dll")
	gdi32                  = syscall.NewLazyDLL("gdi32.dll")
	kernel32               = syscall.NewLazyDLL("kernel32.dll")
	openClipboard          = user32.NewProc("OpenClipboard")
	closeClipboard         = user32.NewProc("CloseClipboard")
	emptyClipboard         = user32.NewProc("EmptyClipboard")
	setClipboardData       = user32.NewProc("SetClipboardData")
	getDC                  = user32.NewProc("GetDC")
	releaseDC              = user32.NewProc("ReleaseDC")
	createCompatibleDC     = gdi32.NewProc("CreateCompatibleDC")
	createCompatibleBitmap = gdi32.NewProc("CreateCompatibleBitmap")
	selectObject           = gdi32.NewProc("SelectObject")
	bitBlt                 = gdi32.NewProc("BitBlt")
	deleteObject           = gdi32.NewProc("DeleteObject")
	getDIBits              = gdi32.NewProc("GetDIBits")
	globalAlloc            = kernel32.NewProc("GlobalAlloc")
	globalLock             = kernel32.NewProc("GlobalLock")
	globalUnlock           = kernel32.NewProc("GlobalUnlock")
)

const (
	SRCCOPY       = 0x00CC0020
	CF_DIB        = 8
	GMEM_MOVEABLE = 0x0002
)

type BITMAPINFOHEADER struct {
	BiSize          uint32
	BiWidth         int32
	BiHeight        int32
	BiPlanes        uint16
	BiBitCount      uint16
	BiCompression   uint32
	BiSizeImage     uint32
	BiXPelsPerMeter int32
	BiYPelsPerMeter int32
	BiClrUsed       uint32
	BiClrImportant  uint32
}

func main() {
	hwnd := uintptr(0)
	hdc, _, _ := getDC.Call(hwnd)
	defer releaseDC.Call(hwnd, hdc)

	memDC, _, _ := createCompatibleDC.Call(hdc)
	defer deleteObject.Call(memDC)

	screenWidth := 1920
	screenHeight := 1080

	hBitmap, _, _ := createCompatibleBitmap.Call(hdc, uintptr(screenWidth), uintptr(screenHeight))
	defer deleteObject.Call(hBitmap)

	oldBitmap, _, _ := selectObject.Call(memDC, hBitmap)
	defer selectObject.Call(memDC, oldBitmap)

	bitBlt.Call(memDC, 0, 0, uintptr(screenWidth), uintptr(screenHeight), hdc, 0, 0, SRCCOPY)

	var bi BITMAPINFOHEADER
	bi.BiSize = uint32(unsafe.Sizeof(bi))
	bi.BiWidth = int32(screenWidth)
	bi.BiHeight = int32(-screenHeight) // top-down DIB
	bi.BiPlanes = 1
	bi.BiBitCount = 24
	bi.BiCompression = 0

	hDIB, _, _ := globalAlloc.Call(GMEM_MOVEABLE, uintptr((screenWidth*screenHeight*3)+int(unsafe.Sizeof(bi))))
	lpDIB, _, _ := globalLock.Call(hDIB)
	defer globalUnlock.Call(hDIB)

	// 取點集的資料，從lpDIB+unsafe.Sizeof(bi)的位置開始寫起
	getDIBits.Call(hdc, hBitmap, 0, uintptr(screenHeight), lpDIB+unsafe.Sizeof(bi), uintptr(unsafe.Pointer(&bi)), 0)
	// 將BITMAPINFOHEADER補上，即寫lpDIB開始寫入BITMAPINFOHEADER的資料
	copy((*[1 << 30]byte)(unsafe.Pointer(lpDIB))[:], (*[1 << 30]byte)(unsafe.Pointer(&bi))[:unsafe.Sizeof(bi)])

	openClipboard.Call(0)
	defer closeClipboard.Call()

	emptyClipboard.Call()
	setClipboardData.Call(CF_DIB, hDIB)

	fmt.Println("Screenshot copied to clipboard as CF_DIB")
}