DWMThumbnail_v1：用 DWM 实时预览窗口画面

做窗口预览时，定时截图再刷新图片虽然直观，但代码量、刷新频率和资源占用都要自己处理。Windows 的 DWM 缩略图接口可以把一个现有窗口的画面实时合成到另一个窗口中，DWMThumbnail_v1 就是把这套接口整理成 AHK v1 可直接使用的类。

这个库源自 thqby 的实现，由 dbgba 移植到 AHK v1。它不需要额外 DLL，核心依赖是系统自带的 dwmapi.dll。

它能完成什么

为指定窗口创建一个独立的实时预览窗口。
按源窗口比例缩放预览，并随预览窗口尺寸变化自动调整。
设置预览透明度，只显示客户区，或临时显示、隐藏缩略图。
查询源窗口尺寸，并通过 updateProperties() 进一步修改 DWM 缩略图属性。

创建对象时可以传窗口句柄，也可以传 AHK 能识别的窗口条件。类内部会保存同一源窗口对应的缩略图对象，避免重复注册。

主要方法怎么理解

new DWMThumbnail(hwnd) 负责注册并显示预览；setOpacity() 接收 0 到 255 的透明度；onlyClientArea(true) 可以排除标题栏和边框；show()、hide() 控制显示状态；不用时调用 Destroy() 释放 DWM 缩略图和 GUI。

示例先创建一个蓝色源窗口，再为它创建实时缩略图。这样不依赖其他软件，适合先确认系统和库能正常工作。

示例代码：DWMThumbnail_v1_示例.ahk

库源码：DWMThumbnail_v1.ahk

; AutoHotkey v1 port of DWMThumbnail.ahk.
; Original author: thqby (https://github.com/thqby/ahk2_lib)
; Ported to AutoHotkey v1 by: dbgba

class DWMThumbnail {
	static thumbnails := {}

	Call(hwnd) {
		hwnd := DWMThumbnail._ResolveHwnd(hwnd)
		if (!hwnd)
			throw Exception("Invalid source window.", -1)
		if (DWMThumbnail.thumbnails.HasKey(hwnd)) {
			thumbnail := DWMThumbnail.thumbnails[hwnd]
			if IsObject(thumbnail)
				return thumbnail
		}
		return new DWMThumbnail(hwnd)
	}

	__New(hwnd) {
		DWMThumbnail._EnsureDwmApi()
		hwnd := DWMThumbnail._ResolveHwnd(hwnd)
		if (!hwnd)
			throw Exception("Invalid source window.", -1)

		this.sourceHwnd := hwnd
		this.ptr := 0
		this._closed := false
		this.guiName := "DWMThumbnail_v1_" hwnd "_" A_TickCount "_" A_Now

		guiName := this.guiName
		DWMThumbnail._EnsureMessageHooks()
		Gui, %guiName%:New, +AlwaysOnTop +E0x08000000 +ToolWindow +Resize -DPIScale +HwndhGui
		this.guiHwnd := hGui

		thumbnail := 0
		hr := DllCall("dwmapi\DwmRegisterThumbnail", "Ptr", hGui, "Ptr", hwnd, "Ptr*", thumbnail, "Int")
		if (hr) {
			Gui, %guiName%:Destroy
			throw DWMThumbnail._Error(hr, -1)
		}

		this.ptr := thumbnail
		DWMThumbnail.thumbnails[hwnd] := this
		guiMap := DWMThumbnail._GuiMap()
		guiMap[hGui] := this
		guiMap[guiName] := this

		this.querySourceSize(w, h)
		showW := Round(w / 2)
		showH := Round(h / 2)
		if (showW < 1)
			showW := 1
		if (showH < 1)
			showH := 1
		Gui, %guiName%:Show, % "w" showW " h" showH " NA", DWMThumbnail
		this.show()
	}

	__Delete() {
		this.Destroy()
	}

	Destroy() {
		if (this._closed)
			return
		this._closed := true

		if (this.ptr) {
			DllCall("dwmapi\DwmUnregisterThumbnail", "Ptr", this.ptr, "Int")
			this.ptr := 0
		}

		if (this.sourceHwnd && DWMThumbnail.thumbnails.HasKey(this.sourceHwnd))
			DWMThumbnail.thumbnails.Delete(this.sourceHwnd)

		guiMap := DWMThumbnail._GuiMap()
		if (this.guiHwnd && guiMap.HasKey(this.guiHwnd))
			guiMap.Delete(this.guiHwnd)
		if (this.guiName != "" && guiMap.HasKey(this.guiName))
			guiMap.Delete(this.guiName)

		if (this.guiName != "") {
			guiName := this.guiName
			Gui, %guiName%:Destroy
			this.guiName := ""
		}
	}

	querySourceSize(ByRef width, ByRef height) {
		VarSetCapacity(size, 8, 0)
		hr := DllCall("dwmapi\DwmQueryThumbnailSourceSize", "Ptr", this.ptr, "Ptr", &size, "Int")
		if (hr)
			throw DWMThumbnail._Error(hr, -1)
		width := NumGet(size, 0, "Int")
		height := NumGet(size, 4, "Int")
	}

	updateProperties(properties) {
		if !IsObject(properties)
			throw Exception("properties must be an object.", -1)

		VarSetCapacity(buf, 48, 0)
		flags := 0
		for k, v in properties {
			key := k
			StringLower, key, key
			if (key = "rcdestination" || key = "dest" || key = "d") {
				flags |= 1
				DWMThumbnail._PutRect(buf, 4, v)
			} else if (key = "rcsource" || key = "src" || key = "s") {
				if IsObject(v) {
					flags |= 2
					DWMThumbnail._PutRect(buf, 20, v)
				}
			} else if (key = "opacity" || key = "o") {
				flags |= 4
				NumPut(v, buf, 36, "UChar")
			} else if (key = "fvisible" || key = "vis" || key = "v") {
				flags |= 8
				NumPut(v ? 1 : 0, buf, 40, "Int")
			} else if (key = "fsourceclientareaonly" || key = "client" || key = "c") {
				flags |= 16
				NumPut(v ? 1 : 0, buf, 44, "Int")
			}
		}

		NumPut(flags, buf, 0, "UInt")
		hr := DllCall("dwmapi\DwmUpdateThumbnailProperties", "Ptr", this.ptr, "Ptr", &buf, "Int")
		if (hr)
			throw DWMThumbnail._Error(hr, -1)
	}

	show(dst := "", src := "") {
		if !IsObject(dst) {
			DWMThumbnail._GetClientSize(this.guiHwnd, w, h)
			dst := [0, 0, w, h]
		}
		guiName := this.guiName
		Gui, %guiName%:Show, NA
		this.updateProperties({v: 1, d: dst, s: src})
	}

	hide() {
		this.updateProperties({v: 0})
		guiName := this.guiName
		Gui, %guiName%:Hide
	}

	onlyClientArea(client := true) {
		this.updateProperties({c: client})
	}

	setOpacity(opacity) {
		this.updateProperties({o: opacity})
	}

	_OnGuiSize(id, minMax, width, height) {
		guiMap := DWMThumbnail._GuiMap()
		if (!guiMap.HasKey(id))
			return
		thumbnail := guiMap[id]
		if (!IsObject(thumbnail) || !thumbnail.ptr || width = "" || height = "" || width <= 0 || height <= 0)
			return
		DWMThumbnail._UpdateToClientSize(thumbnail.ptr, width, height)
	}

	_OnGuiClose(id) {
		guiMap := DWMThumbnail._GuiMap()
		if (!guiMap.HasKey(id))
			return
		thumbnail := guiMap[id]
		if IsObject(thumbnail)
			thumbnail.Destroy()
	}

	_UpdateToClientSize(thumbnail, width, height) {
		VarSetCapacity(buf, 48, 0)
		NumPut(1, buf, 0, "UInt")
		VarSetCapacity(size, 8, 0)
		hr := DllCall("dwmapi\DwmQueryThumbnailSourceSize", "Ptr", thumbnail, "Ptr", &size, "Int")
		if (!hr) {
			w := NumGet(size, 0, "Int")
			h := NumGet(size, 4, "Int")
			if (w > 0 && h > 0 && w * height > width * h) {
				h0 := Round(h * width / w)
				h1 := Round((height - h0) / 2)
				DWMThumbnail._PutRect(buf, 4, [0, h1, width, h0 + h1])
			} else if (w > 0 && h > 0) {
				w0 := Round(w * height / h)
				w1 := Round((width - w0) / 2)
				DWMThumbnail._PutRect(buf, 4, [w1, 0, w0 + w1, height])
			} else {
				DWMThumbnail._PutRect(buf, 4, [0, 0, width, height])
			}
		} else {
			DWMThumbnail._PutRect(buf, 4, [0, 0, width, height])
		}
		DllCall("dwmapi\DwmUpdateThumbnailProperties", "Ptr", thumbnail, "Ptr", &buf, "Int")
	}

	_PutRect(ByRef buf, offset, rc) {
		NumPut(rc[1], buf, offset + 0, "Int")
		NumPut(rc[2], buf, offset + 4, "Int")
		NumPut(rc[3], buf, offset + 8, "Int")
		NumPut(rc[4], buf, offset + 12, "Int")
	}

	_GetClientSize(hwnd, ByRef width, ByRef height) {
		VarSetCapacity(rc, 16, 0)
		DllCall("GetClientRect", "Ptr", hwnd, "Ptr", &rc, "Int")
		width := NumGet(rc, 8, "Int") - NumGet(rc, 0, "Int")
		height := NumGet(rc, 12, "Int") - NumGet(rc, 4, "Int")
	}

	_ResolveHwnd(hwnd) {
		if hwnd is integer
			return hwnd + 0
		return WinExist(hwnd)
	}

	_GuiMap() {
		static guiMap := {}
		return guiMap
	}

	_EnsureMessageHooks() {
		static hooked := false
		if (hooked)
			return
		hooked := true
		OnMessage(0x0005, "DWMThumbnail_v1_WM_SIZE")
		OnMessage(0x0010, "DWMThumbnail_v1_WM_CLOSE")
	}

	_EnsureDwmApi() {
		static hDwmApi := 0
		if (!hDwmApi)
			hDwmApi := DllCall("LoadLibrary", "Str", "dwmapi.dll", "Ptr")
		if (!hDwmApi)
			throw Exception("LoadLibrary failed for dwmapi.dll.", -1, A_LastError)
		return hDwmApi
	}

	_Error(hr, what := -1) {
		return Exception("DWM call failed.", what, Format("0x{:08X}", hr & 0xFFFFFFFF))
	}
}

; GUI messages are handled with functions instead of labels so this file can be included at the top of a v1 script.
DWMThumbnail_v1_WM_SIZE(wParam, lParam, msg, hwnd) {
	guiMap := DWMThumbnail._GuiMap()
	if (!guiMap.HasKey(hwnd))
		return
	width := lParam & 0xFFFF
	height := (lParam >> 16) & 0xFFFF
	DWMThumbnail._OnGuiSize(hwnd, wParam, width, height)
}

DWMThumbnail_v1_WM_CLOSE(wParam, lParam, msg, hwnd) {
	guiMap := DWMThumbnail._GuiMap()
	if (!guiMap.HasKey(hwnd))
		return
	DWMThumbnail._OnGuiClose(hwnd)
	return 0
}

使用边界

DWM Thumbnail 是系统合成出来的实时预览，不是截图文件，因此不能直接拿到像素数据做保存、识别或编辑。源窗口也必须仍然存在；源窗口关闭后，应及时销毁对应对象。

它更适合窗口监看、小窗预览、GUI 中展示其他程序状态。需要真正截屏、离屏取图或图像识别时，应改用截图类库或 WinCapture 一类方案。

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DWMThumbnail_v1：用 DWM 实时预览窗口画面

它能完成什么

主要方法怎么理解

示例代码：DWMThumbnail_v1_示例.ahk

库源码：DWMThumbnail_v1.ahk

使用边界

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DWMThumbnail_v1：用 DWM 实时预览窗口画面

它能完成什么

主要方法怎么理解

示例代码：DWMThumbnail_v1_示例.ahk

库源码：DWMThumbnail_v1.ahk

使用边界

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