制作一个具有我的应用程序透明背景的全屏绘画程序

我的目标是制作一个小型 PC/Windows 程序，它允许我在屏幕顶部进行绘制，并将结果保存为具有透明背景的 png 格式。像这样的软件Epic Pen https://epic-pen.com/ or gInk https://github.com/geovens/gInk但我的方式。全部使用 Python 3.7 和 PyQt5。

到目前为止，我设法得到了一个功能性的绘图应用程序（基本上遵循本教程 https://www.youtube.com/watch?v=qEgyGyVA1ZQ）因为我同时在学习PyQt。我设法将草稿保存为具有透明背景的 png。我可以使画板全屏且无边框。

现在的问题是，我找不到一种方法使整个背景透明。尽管我找到了使用以下方法使窗口透明且无边框的方法：

Window = Window()
Window.setStyleSheet("background:transparent;")
Window.setAttribute(Qt.WA_TranslucentBackground)
Window.setWindowFlags(Qt.FramelessWindowHint)
Window.show()

它有效......直到我有一个绘图区域。我可以在它上面画画，它会以透明背景保存，但它显示黑色。

所以我正在寻找这个解决方案。即使没有 PyQt，我也不在乎，只要我能让我的程序运行即可。

So here is what I have (I show you windowed with the frame to make it easier to explain):

And here is what I want:

这是我的代码：

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow, QMenuBar, QMenu, QAction, QShortcut, QFileDialog
from PyQt5.QtGui import QIcon, QImage, QPainter, QPen
from PyQt5.QtCore import Qt, QPoint


class Window(QMainWindow):
    def __init__(self):
        super().__init__()

        top = 400
        left = 400
        width = 800
        height = 600

        icon = "icons/icon.png"

        self.setWindowTitle("ScreenPen drawing board")
        self.setGeometry(top, left, width, height)
        self.setWindowIcon(QIcon(icon))

# ---------- sets image ----------
        self.image = QImage(self.size(), QImage.Format_RGBA64)
        self.image.fill(Qt.transparent)

# ---------- init drawing state ----------
        self.drawing = False
        self.brushSize = 2
        self.brushColor = Qt.red
        self.lastPoint = QPoint()

# ---------- Define Menus ----------
    # mainmenu
        mainMenu = self.menuBar()
        fileMenu = mainMenu.addMenu("File")
        toolMenu = mainMenu.addMenu("Tool")
        toolColor = mainMenu.addMenu("Color")
    # smenu save
        saveAction = QAction(QIcon("icons/save.png"), "Save", self)
        saveAction.setShortcut("Ctrl+S")
        fileMenu.addAction(saveAction)
        saveAction.triggered.connect(self.saveFrame)
    # smenu clear frame
        clearFrameAction = QAction(QIcon("icons/clear.png"), "Clear Frame", self)
        clearFrameAction.setShortcut("Ctrl+Del")
        fileMenu.addAction(clearFrameAction)
        clearFrameAction.triggered.connect(self.clearFrame)
    # smenu Tool Pen
        toolPenAction = QAction(QIcon("icons/toolPen.png"), "Pen", self)
        # clearAction.setShortcut("Ctrl+Del")
        toolMenu.addAction(toolPenAction)

# ---------- Catch Mouse Down --------

    def mousePressEvent(self, event):
        if event.button() == Qt.LeftButton:
            self.drawing = True
            self.lastPoint = event.pos()

# ---------- Catch Mouse Move --------
    def mouseMoveEvent(self, event):
        if (event.buttons() & Qt.LeftButton) & self.drawing:
            painter = QPainter(self.image)
            painter.setPen(QPen(self.brushColor, self.brushSize, Qt.SolidLine, Qt.RoundCap, Qt.RoundJoin))
            painter.drawLine(self.lastPoint, event.pos())
            self.lastPoint = event.pos()
            self.update()

# ---------- Catch Mouse Up --------
    def mouseReleaseEvent(self, event):
        if event.button == Qt.LeftButton:
            self.drawing = False

# ---------- Paint --------
    def paintEvent(self, event):
        canvasPainter = QPainter(self)
        canvasPainter.drawImage(self.rect(), self.image, self.image.rect())

# ---------- Save Action ----------
    def saveFrame(self):
        filePath,  _ = QFileDialog.getSaveFileName(self, "Save Image", "", "PNG(*.png);;JPEG(*.jpg *.jpeg);; ALL Files(*.*)")
        if filePath == "":
            return
        self.image.save(filePath)

# ---------- Clear Frame Action ----------
    def clearFrame(self):
        self.image.fill(Qt.white)
        self.update()

if __name__ == "__main__":
    app = QApplication(sys.argv)
    Window = Window()
    # Window style
    Window.setStyleSheet("background:transparent;")
    Window.setAttribute(Qt.WA_TranslucentBackground)
    # Window.setWindowFlags(Qt.FramelessWindowHint)
    Window.show()
    app.exec()

实现此目的的一种方法（应该适用于大多数平台）是创建整个桌面的图像，然后将其裁剪到窗口覆盖的区域。这可以在 Qt 中轻松完成，使用QScreen.grabWindow https://doc.qt.io/qt-5/qscreen.html#grabWindow:

def saveFrame(self):
    filePath,  _ = QFileDialog.getSaveFileName(self, "Save Image", "", "PNG(*.png);;JPEG(*.jpg *.jpeg);; ALL Files(*.*)")
    if filePath == "":
        return

    screen = QApplication.desktop().windowHandle().screen()
    wid = QApplication.desktop().winId()
    pixmap = screen.grabWindow(wid, self.x(), self.y(), self.width(), self.height())
    pixmap.save(filePath)

或者可能：

    screen = self.windowHandle().screen()
    pixmap = screen.grabWindow(0, self.x(), self.y(), self.width(), self.height())
    pixmap.save(filePath)

这些都在 Linux 上适用于我，但我还没有在其他平台上测试过它们。如果您还想获取窗框，请使用self.frameGeometry()以获得所需的尺寸。