python - 弧形中的不同颜色

Question

考虑以下玩具示例:

from PyQt5 import QtWidgets, QtGui, QtCore

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

        w = QtWidgets.QWidget()
        layout = QtWidgets.QVBoxLayout()
        w.setLayout(layout)
        self.setCentralWidget(w)

        label = QtWidgets.QLabel()
        canvas = QtGui.QPixmap(400, 300)
        label.setPixmap(canvas)
        layout.addWidget(label)

        def paintEvent():
            painter = QtGui.QPainter(label.pixmap())
            painter.setRenderHint(QtGui.QPainter.Antialiasing)
            painter.setPen(QtCore.Qt.red)
            painter.drawArc(0, 0, 100, 100, 1440, -2880)
            painter.end()

        paintEvent()

        self.show()

app = QtWidgets.QApplication([])
window = MainWindow()
app.exec_()

我怎样才能使用任意数量的颜色(最好是不同长度的)来绘制弧线？

我尝试用渐变(线性和圆锥形)来做，但我一直无法获得准确的结果。

我想更广泛的问题是，在绘制弧线时，我能否以某种方式使用不同的笔颜色？请注意，圆弧可以是半圆、整圆或介于两者之间的任何形状。

颜色将使用百分比分布。每种颜色都是弧长的一部分。但我对所有颜色均等间距的解决方案感到满意。

Answer 1

一个可能的解决方案是分段绘制圆弧:

from PyQt5 import QtCore, QtGui, QtWidgets


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

        w = QtWidgets.QWidget()
        layout = QtWidgets.QVBoxLayout()
        w.setLayout(layout)
        self.setCentralWidget(w)

        label = QtWidgets.QLabel()
        canvas = QtGui.QPixmap(400, 300)
        canvas.fill(QtGui.QColor("white"))
        label.setPixmap(canvas)
        layout.addWidget(label)

        def paint_label():
            painter = QtGui.QPainter(label.pixmap())
            painter.setRenderHint(QtGui.QPainter.Antialiasing)
            r = QtCore.QRect(0, 0, 100, 100)
            delta_angle = -180 * 16
            start_angle = 90 * 16
            values = (1, 2, 3, 4)
            colors = (
                QtGui.QColor("red"),
                QtGui.QColor("blue"),
                QtGui.QColor("green"),
                QtGui.QColor("yellow"),
            )
            sum_of_values = sum(values)
            for value, color in zip(values, colors):
                end_angle = start_angle + int((value/sum_of_values) * delta_angle)
                painter.setPen(color)
                painter.drawArc(r, start_angle, end_angle - start_angle)
                start_angle = end_angle
            painter.end()

        paint_label()

        self.show()


def main():

    app = QtWidgets.QApplication([])
    window = MainWindow()
    app.exec_()


if __name__ == "__main__":
    main()