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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Issue with DPI corrections with Qt5 backend","articleBody":"I am running into issues with Matplotlib 2.0 with the Qt5 backend. The following script:\r\n\r\n```python\r\nimport matplotlib\r\nmatplotlib.use('Qt5Agg')\r\nimport matplotlib.pyplot as plt\r\n\r\nfig = plt.figure()\r\nax = fig.add_axes([0, 0, 1, 1])\r\n\r\nprint(ax.transData.transform((0.0, 0.0)))\r\nprint(ax.transData.transform((0.5, 0.5)))\r\nprint(ax.transData.transform((1.0, 1.0)))\r\nprint(fig.canvas.width(), fig.canvas.height())\r\n```\r\n\r\nreturns\r\n\r\n```\r\n[ 0.  0.]\r\n[ 640.  480.]\r\n[ 1280.   960.]\r\n320 240\r\n```\r\n\r\nwith Qt5, and:\r\n\r\n```\r\n[ 0. 0.]\r\n[ 320. 240.]\r\n[ 640. 480.]\r\n(640, 480)\r\n```\r\n\r\nwith Qt4. In Qt5 there is a factor of 4x difference between the display coordinates and the size of the widget, where I think there should only be a factor of 2x. A more visual way to see this issue is to run:\r\n\r\n```python\r\nfrom PyQt5 import QtGui, QtWidgets\r\nfrom matplotlib.figure import Figure\r\nfrom matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas\r\n\r\n\r\nclass MplCanvas(FigureCanvas):\r\n\r\n    def __init__(self, fig):\r\n        FigureCanvas.__init__(self, fig)\r\n        self.renderer = None\r\n        self.x = self.y = 0\r\n\r\n    def paintEvent(self, event):\r\n\r\n        if self.renderer is None:\r\n            self.renderer = self.get_renderer()\r\n\r\n        super(MplCanvas, self).paintEvent(event)\r\n\r\n        p = QtGui.QPainter(self)\r\n        pen = QtGui.QPen(QtGui.QColor('black'))\r\n        pen.setWidth(20)\r\n        p.setPen(pen)\r\n        p.drawPoint(self.x, self.y)\r\n\r\n    def mouse_press(self, event):\r\n        x, y = ax.transData.transform((event.xdata, event.ydata))\r\n        self.x, self.y = x, self.height() - y\r\n        self.update()\r\n\r\n\r\napp = QtWidgets.QApplication([''])\r\n\r\nfig = Figure()\r\ncanvas = MplCanvas(fig)\r\nax = fig.add_axes([0, 0, 1, 1])\r\n\r\nprint(ax.transData.transform((0.0, 0.0)))\r\nprint(ax.transData.transform((0.5, 0.5)))\r\nprint(ax.transData.transform((1.0, 1.0)))\r\nprint(canvas.width(), canvas.height())\r\n\r\ncanvas.mpl_connect('button_press_event', canvas.mouse_press)\r\ncanvas.mpl_connect('motion_notify_event', canvas.mouse_press)\r\n\r\ncanvas.show()\r\napp.exec_()\r\n```\r\n\r\nThis shows a window where if you move around the cursor, a black square should follow it. With Qt5, the square is offset by a factor of 2x:\r\n\r\n\u003cimg width=\"378\" alt=\"untitled\" src=\"https://cloud.githubusercontent.com/assets/314716/22799480/d005a51e-eefd-11e6-8acd-62070f6570db.png\"\u003e\r\n\r\ncc @tacaswell","author":{"url":"https://github.com/astrofrog","@type":"Person","name":"astrofrog"},"datePublished":"2017-02-09T19:28:08.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":22},"url":"https://github.com/8052/matplotlib/issues/8052"}