使用 PYQT 绘画

Question

我正在尝试在 PYQT 中实现类似 Paint 的程序。我正在尝试使用 PYQT 包中的 Scribble 示例的代码，该代码可以在：C:\Python26\Lib\site-packages\PyQt4\examples\widgets 中找到。现在关于这个我有两个问题：

1. 在 Scribble 程序中，绘画时，当您按住鼠标按钮并涂鸦时，绘画不会实时更新。我发现这个问题来自ScribbleArea类中的函数drawLineTo，该行：

self.update(QtCore.QRect(self.lastPoint, endPoint).normalized().adjusted(-rad, -rad, +rad , +rad))

现在，如果我简单地替换这一行，

self.update()

问题就解决了，但光标不在绘画发生的确切位置。

你知道我可以在 self.update() 中添加哪些参数来解决这两个问题吗？

1. 我想像 Scribble 一样打开一个图像并在其上绘画，然后仅保存带有空白的绘画，比如说白色背景（背景中没有原始图像）。你能告诉我该怎么做吗？

我将不胜感激您对其中任何一个问题的回答。

谢谢！

Answer 1

刚刚学习 pyqt，但我修改了代码以解决光标不匹配问题（并修改了 openImage 方法以保持图像大小与窗口同步）：

#!/usr/bin/env python


#############################################################################
##
## Copyright (C) 2010 Riverbank Computing Limited.
## Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
## All rights reserved.
##
## This file is part of the examples of PyQt.
##
## $QT_BEGIN_LICENSE:BSD$
## You may use this file under the terms of the BSD license as follows:
##
## "Redistribution and use in source and binary forms, with or without
## modification, are permitted provided that the following conditions are
## met:
##   * Redistributions of source code must retain the above copyright
##     notice, this list of conditions and the following disclaimer.
##   * Redistributions in binary form must reproduce the above copyright
##     notice, this list of conditions and the following disclaimer in
##     the documentation and/or other materials provided with the
##     distribution.
##   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
##     the names of its contributors may be used to endorse or promote
##     products derived from this software without specific prior written
##     permission.
##
## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
## "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
## LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
## A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
## OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
## SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
## LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
## DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
## THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
## (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
## $QT_END_LICENSE$
##
#############################################################################


# These are only needed for Python v2 but are harmless for Python v3.
import sip
sip.setapi('QString', 2)
sip.setapi('QVariant', 2)

from PyQt4 import QtCore, QtGui


class ScribbleArea(QtGui.QWidget):
    """
      this scales the image but it's not good, too many refreshes really mess it up!!!
    """
    def __init__(self, parent=None):
        super(ScribbleArea, self).__init__(parent)

        self.setAttribute(QtCore.Qt.WA_StaticContents)
        self.modified = False
        self.scribbling = False
        self.myPenWidth = 1
        self.myPenColor = QtCore.Qt.blue
        imageSize = QtCore.QSize(500, 500)
#       self.image = QtGui.QImage()
        self.image = QtGui.QImage(imageSize, QtGui.QImage.Format_RGB32)
        self.lastPoint = QtCore.QPoint()

    def openImage(self, fileName):
        loadedImage = QtGui.QImage()
        if not loadedImage.load(fileName):
            return False

        w = loadedImage.width()
        h = loadedImage.height()    
        self.mainWindow.resize(w, h)

#       newSize = loadedImage.size().expandedTo(self.size())
#       self.resizeImage(loadedImage, newSize)
        self.image = loadedImage
        self.modified = False
        self.update()
        return True

    def saveImage(self, fileName, fileFormat):
        visibleImage = self.image
        self.resizeImage(visibleImage, self.size())

        if visibleImage.save(fileName, fileFormat):
            self.modified = False
            return True
        else:
            return False

    def setPenColor(self, newColor):
        self.myPenColor = newColor

    def setPenWidth(self, newWidth):
        self.myPenWidth = newWidth

    def clearImage(self):
        self.image.fill(QtGui.qRgb(255, 255, 255))
        self.modified = True
        self.update()

    def mousePressEvent(self, event):
#       print "self.image.width() = %d" % self.image.width()
#       print "self.image.height() = %d" % self.image.height()
#       print "self.image.size() = %s" % self.image.size()
#       print "self.size() = %s" % self.size()
#       print "event.pos() = %s" % event.pos()
        if event.button() == QtCore.Qt.LeftButton:
            self.lastPoint = event.pos()
            self.scribbling = True

    def mouseMoveEvent(self, event):
        if (event.buttons() & QtCore.Qt.LeftButton) and self.scribbling:
            self.drawLineTo(event.pos())

    def mouseReleaseEvent(self, event):
        if event.button() == QtCore.Qt.LeftButton and self.scribbling:
            self.drawLineTo(event.pos())
            self.scribbling = False

    def paintEvent(self, event):
        painter = QtGui.QPainter(self)
        painter.drawImage(event.rect(), self.image)

    def resizeEvent(self, event):
#       print "resize event"
#       print "event = %s" % event
#       print "event.oldSize() = %s" % event.oldSize()
#       print "event.size() = %s" % event.size()

        self.resizeImage(self.image, event.size())

#       if self.width() > self.image.width() or self.height() > self.image.height():
#           newWidth = max(self.width() + 128, self.image.width())
#           newHeight = max(self.height() + 128, self.image.height())
#           print "newWidth = %d, newHeight = %d" % (newWidth, newHeight)
#           self.resizeImage(self.image, QtCore.QSize(newWidth, newHeight))
#           self.update()

        super(ScribbleArea, self).resizeEvent(event)

    def drawLineTo(self, endPoint):
        painter = QtGui.QPainter(self.image)
        painter.setPen(QtGui.QPen(self.myPenColor, self.myPenWidth,
            QtCore.Qt.SolidLine, QtCore.Qt.RoundCap, QtCore.Qt.RoundJoin))
        painter.drawLine(self.lastPoint, endPoint)
        self.modified = True

        # rad = self.myPenWidth / 2 + 2
        # self.update(QtCore.QRect(self.lastPoint, endPoint).normalized().adjusted(-rad, -rad, +rad, +rad))
        self.update()
        self.lastPoint = QtCore.QPoint(endPoint)

    def resizeImage(self, image, newSize):
        if image.size() == newSize:
            return

#       print "image.size() = %s" % repr(image.size())
#       print "newSize = %s" % newSize

# this resizes the canvas without resampling the image
        newImage = QtGui.QImage(newSize, QtGui.QImage.Format_RGB32)
        newImage.fill(QtGui.qRgb(255, 255, 255))
        painter = QtGui.QPainter(newImage)
        painter.drawImage(QtCore.QPoint(0, 0), image)


##  this resampled the image but it gets messed up with so many events...       
##      painter.setRenderHint(QtGui.QPainter.SmoothPixmapTransform, True)
##      painter.setRenderHint(QtGui.QPainter.HighQualityAntialiasing, True)
#       
#       newImage = QtGui.QImage(newSize, QtGui.QImage.Format_RGB32)
#       newImage.fill(QtGui.qRgb(255, 255, 255))
#       painter = QtGui.QPainter(newImage)
#       srcRect = QtCore.QRect(QtCore.QPoint(0,0), image.size())
#       dstRect = QtCore.QRect(QtCore.QPoint(0,0), newSize)
##      print "srcRect = %s" % srcRect
##      print "dstRect = %s" % dstRect
#       painter.drawImage(dstRect, image, srcRect)


        self.image = newImage

    def print_(self):
        printer = QtGui.QPrinter(QtGui.QPrinter.HighResolution)

        printDialog = QtGui.QPrintDialog(printer, self)
        if printDialog.exec_() == QtGui.QDialog.Accepted:
            painter = QtGui.QPainter(printer)
            rect = painter.viewport()
            size = self.image.size()
            size.scale(rect.size(), QtCore.Qt.KeepAspectRatio)
            painter.setViewport(rect.x(), rect.y(), size.width(), size.height())
            painter.setWindow(self.image.rect())
            painter.drawImage(0, 0, self.image)
            painter.end()

    def isModified(self):
        return self.modified

    def penColor(self):
        return self.myPenColor

    def penWidth(self):
        return self.myPenWidth


class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()

        self.saveAsActs = []

        self.scribbleArea = ScribbleArea(self)
        self.scribbleArea.clearImage()
        self.scribbleArea.mainWindow = self  # maybe not using this?
        self.setCentralWidget(self.scribbleArea)

        self.createActions()
        self.createMenus()

        self.setWindowTitle("Scribble")
        self.resize(500, 500)

    def closeEvent(self, event):
        if self.maybeSave():
            event.accept()
        else:
            event.ignore()

    def open(self):
        if self.maybeSave():
            fileName = QtGui.QFileDialog.getOpenFileName(self, "Open File",
                QtCore.QDir.currentPath())
            if fileName:
                self.scribbleArea.openImage(fileName)

    def save(self):
        action = self.sender()
        fileFormat = action.data()
        self.saveFile(fileFormat)

    def penColor(self):
        newColor = QtGui.QColorDialog.getColor(self.scribbleArea.penColor())
        if newColor.isValid():
            self.scribbleArea.setPenColor(newColor)

    def penWidth(self):
        newWidth, ok = QtGui.QInputDialog.getInteger(self, "Scribble",
            "Select pen width:", self.scribbleArea.penWidth(), 1, 50, 1)
        if ok:
            self.scribbleArea.setPenWidth(newWidth)

    def about(self):
        QtGui.QMessageBox.about(self, "About Scribble",
            "<p>The <b>Scribble</b> example shows how to use "
            "QMainWindow as the base widget for an application, and how "
            "to reimplement some of QWidget's event handlers to receive "
            "the events generated for the application's widgets:</p>"
            "<p> We reimplement the mouse event handlers to facilitate "
            "drawing, the paint event handler to update the application "
            "and the resize event handler to optimize the application's "
            "appearance. In addition we reimplement the close event "
            "handler to intercept the close events before terminating "
            "the application.</p>"
            "<p> The example also demonstrates how to use QPainter to "
            "draw an image in real time, as well as to repaint "
            "widgets.</p>")

    def createActions(self):
        self.openAct = QtGui.QAction("&Open...", self, shortcut="Ctrl+O",
            triggered=self.open)

        for format in QtGui.QImageWriter.supportedImageFormats():
            format = str(format)

            text = format.upper() + "..."

            action = QtGui.QAction(text, self, triggered=self.save)
            action.setData(format)
            self.saveAsActs.append(action)

        self.printAct = QtGui.QAction("&Print...", self,
            triggered=self.scribbleArea.print_)

        self.exitAct = QtGui.QAction("E&xit", self, shortcut="Ctrl+Q",
            triggered=self.close)

        self.penColorAct = QtGui.QAction("&Pen Color...", self,
            triggered=self.penColor)

        self.penWidthAct = QtGui.QAction("Pen &Width...", self,
            triggered=self.penWidth)

        self.clearScreenAct = QtGui.QAction("&Clear Screen", self,
            shortcut="Ctrl+L", triggered=self.scribbleArea.clearImage)

        self.aboutAct = QtGui.QAction("&About", self, triggered=self.about)

        self.aboutQtAct = QtGui.QAction("About &Qt", self,
            triggered=QtGui.qApp.aboutQt)

    def createMenus(self):
        self.saveAsMenu = QtGui.QMenu("&Save As", self)
        for action in self.saveAsActs:
            self.saveAsMenu.addAction(action)

        fileMenu = QtGui.QMenu("&File", self)
        fileMenu.addAction(self.openAct)
        fileMenu.addMenu(self.saveAsMenu)
        fileMenu.addAction(self.printAct)
        fileMenu.addSeparator()
        fileMenu.addAction(self.exitAct)

        optionMenu = QtGui.QMenu("&Options", self)
        optionMenu.addAction(self.penColorAct)
        optionMenu.addAction(self.penWidthAct)
        optionMenu.addSeparator()
        optionMenu.addAction(self.clearScreenAct)

        helpMenu = QtGui.QMenu("&Help", self)
        helpMenu.addAction(self.aboutAct)
        helpMenu.addAction(self.aboutQtAct)

        self.menuBar().addMenu(fileMenu)
        self.menuBar().addMenu(optionMenu)
        self.menuBar().addMenu(helpMenu)

    def maybeSave(self):
        if self.scribbleArea.isModified():
            ret = QtGui.QMessageBox.warning(self, "Scribble",
                "The image has been modified.\n"
                "Do you want to save your changes?",
                QtGui.QMessageBox.Save | QtGui.QMessageBox.Discard |
                QtGui.QMessageBox.Cancel)
            if ret == QtGui.QMessageBox.Save:
                return self.saveFile('png')
            elif ret == QtGui.QMessageBox.Cancel:
                return False

        return True

    def saveFile(self, fileFormat):
        initialPath = QtCore.QDir.currentPath() + '/untitled.' + fileFormat

        fileName = QtGui.QFileDialog.getSaveFileName(self, "Save As",
            initialPath,
            "%s Files (*.%s);;All Files (*)" % (fileFormat.upper(), fileFormat))
        if fileName:
            return self.scribbleArea.saveImage(fileName, fileFormat)

        return False


if __name__ == '__main__':

    import sys

    app = QtGui.QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())