qt - 如何在不缩放笔宽的情况下在 QGraphicsScene 上绘图？

Question

我正在尝试在 QGraphicScene 数据上绘图，该数据可以根据情况按数量级变化。由于我使用的笔是装饰性的，我希望 View 与数据的大小无关。但我得到的是:

噪声乘以 50000 的正弦波:



噪声乘以 50 的正弦波:



但是，如果我放大到这些图中的任何一个(两者都放大相同的数量)，当两个图像看起来相同时，我最终会达到一个水平:




这里发生了什么？为什么笔的宽度会因为数据值更大而改变。为什么放大后缩放会消失？

重现这一点的代码如下。左键单击图放大，右键单击缩小。

import sys

from PyQt4 import QtGui as QG
from PyQt4 import QtCore as QC

import numpy as n

class ZoomView(QG.QGraphicsView):
    """Zoomable QGraphicsView"""
    def mouseReleaseEvent(self,event):
        if event.button() == QC.Qt.LeftButton:
            self.scale(1.5,1)
        elif event.button() == QC.Qt.RightButton:
            self.scale(1/1.5,1)

class MainUI(QG.QDialog):
    def __init__(self, parent=None):
        super(MainUI, self).__init__(parent)

        layout = QG.QVBoxLayout()
        self.setLayout(layout)
        button_layout = QG.QHBoxLayout()
        pb3 = QG.QPushButton('add plot')
        button_layout.addWidget(pb3)
        layout.addLayout(button_layout)
        pb3.clicked.connect(self.scene_maker_singleshot)
        scene = QG.QGraphicsScene()
        view = ZoomView(self)
        view.setTransformationAnchor(QG.QGraphicsView.AnchorUnderMouse)
        view.setRenderHint(QG.QPainter.Antialiasing)
        layout.addWidget(view)
        view.setScene(scene)

        self.view = view
        self.scene = scene

    def scene_maker_singleshot(self):
        """Draw scene and fit in view"""
        t1 = 50
        t2 = 100
        QC.QTimer.singleShot(t1, self.make_scene)
        QC.QTimer.singleShot(t2, lambda: self.view.fitInView(self.view.sceneRect()))


    def make_scene(self):
        scale = 50
        #scale = 50000
        noise_amp = 0.2*scale
        points = 1000

        xdata = n.arange(points)
        #generate sine data and random noise
        ydata = n.sin(xdata/(points/10.))*scale +\
                n.random.randint(noise_amp, size=points)
        pen = QG.QPen(QG.QColor("red"))

        for i in xrange(1, xdata.size):
            self.scene.addLine(xdata[i-1], ydata[i-1], xdata[i], ydata[i], pen)


if __name__=="__main__":
    app = QG.QApplication(sys.argv)
    gui = MainUI()
    gui.setFixedSize(500,500)
    gui.show()
    app.exec_()

Answer 1

就像 Mad Physicist 告诉您的那样，将笔设置为化妆品或线宽为 0(行为相同)，您将拥有一支非缩​​放笔。

>> pen.setCosmetic(True);