在 pyqt4 中旋转像素图会产生不需要的翻译 [英] Rotating a pixmap in pyqt4 gives undesired translation

问题描述

我正在尝试编写一个简单的应用程序，该应用程序在按下按钮时旋转 png 图像.我一切正常，只是当图像旋转时，它会在东南方向偏离它的中心.我本来以为它没有绕着中心旋转，但它每旋转 45 度就回到原点，这很奇怪.

在一个关键事件上，我只是调用:

pixmap = pixmap.transformed(QtGui.QTransform().rotate(-self.rot), QtCore.Qt.SmoothTransformation)

有没有办法设置变换的原点来阻止图像四处移动?

解决方案

一个简单的解决方案，如果你使用的是

或者，这篇文章:无法让图像在 Qt 中心旋转，如果您直接使用 QPainter 绘制 QPixmap，似乎可以解决您的问题.

I'm trying to write a simple application that rotates a png image when a button is pressed. I have it all working fine except that as the image rotates it deviates from it's centre in a south-east direction. I would have thought it wasn't rotating around its centre, but it returns to the origin every 45 degrees of rotation, which is strange.

On a key event I'm simply calling:

pixmap = pixmap.transformed(QtGui.QTransform().rotate(-self.rot), QtCore.Qt.SmoothTransformation)

Is there a way to set the origin of the transformation to stop the image moving around?

解决方案

A simple solution, if you are using a QLabel to draw the QPixmap, is to set the alignment of the QLabel to AlignCenter. Moreover, to avoid an initial resizing of the QLabel during the first 45 degrees of the image rotation, the minimum size of the QLabel can be set to the value of the pixmap's diagonal. The image should then properly rotate around its centre without any unwanted back-and-forth translation.

Below I demonstrate how this can be done in a simple application:

import sys
from PyQt4 import QtGui, QtCore
import urllib

class myApplication(QtGui.QWidget):
    def __init__(self, parent=None):
        super(myApplication, self).__init__(parent)

        #---- Prepare a Pixmap ----

        url = ('http://sstatic.net/stackexchange/img/logos/' +
               'careers/careers-icon.png?v=0288ba302bf6')
        self.img = QtGui.QImage()
        self.img.loadFromData(urllib.urlopen(url).read())

        pixmap = QtGui.QPixmap(self.img)

        #---- Embed Pixmap in a QLabel ----

        diag = (pixmap.width()**2 + pixmap.height()**2)**0.5

        self.label = QtGui.QLabel()
        self.label.setMinimumSize(diag, diag)
        self.label.setAlignment(QtCore.Qt.AlignCenter)
        self.label.setPixmap(pixmap)

        #---- Prepare a Layout ----

        grid = QtGui.QGridLayout()

        button = QtGui.QPushButton('Rotate 15 degrees')
        button.clicked.connect(self.rotate_pixmap)

        grid.addWidget(self.label, 0, 0)
        grid.addWidget(button, 1, 0)

        self.setLayout(grid)

        self.rotation = 0

    def rotate_pixmap(self):

        #---- rotate ----

        # Rotate from initial image to avoid cumulative deformation from
        # transformation

        pixmap = QtGui.QPixmap(self.img)
        self.rotation += 15

        transform = QtGui.QTransform().rotate(self.rotation)
        pixmap = pixmap.transformed(transform, QtCore.Qt.SmoothTransformation)

        #---- update label ----

        self.label.setPixmap(pixmap)

if __name__ == '__main__':

    app = QtGui.QApplication(sys.argv)

    instance = myApplication()  
    instance.show()    

    sys.exit(app.exec_())

Which results in:

Alternatively, this post : can't get the image to rotate in center in Qt, seems to address your issue if you are painting the QPixmap directly with QPainter.

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