引言

圖形與圖像繪制支持是一個GUI框架庫的核心模塊之一，從Java的Graphics2D到Android的Canvas類支持到PyQT5中的QPainter類支持與圖元支持，都很好的滿足了GUI庫的圖形繪制與渲染需求。

QPainter類介紹

QPainter類是PyQT5中圖形繪制類，支持圓、橢圓、矩形、圓角矩形、線段、文本、圖像、多邊形、弧形等常見幾何形狀的繪制與填充，支持顏色、旋轉、狀態復位、平移、錯切等設置操作。所有的QWidget類都繼承了paintEvent方法，繪制代碼都應該在paintEvent方法中完成執行。一個典型的paintEvent方法繪制代碼如下：

def paintEvent(self, paintEvent):
    painter = QPainter(self)
    painter.setPen(Qt.blue)
    painter.setFont(QFont("Arial", 30))
    painter.drawText(rect(), Qt.AlignCenter, "OpenCV學堂")

def paintEvent(self, paintEvent):
    p = QPainter()
    p.begin(self)
    p.drawLine(...)         # drawing code
    p.end()

調用系統繪制

def paintEvent(self, paintEvent):
    p = QPainter(self)
    p.drawLine(...)         # drawing code

綜合代碼演示

代碼實現了繪制與填充不同的幾何形狀，支持不同顏色設置，線寬設置，風格設置等。運行結果如下圖：

添加上顯示圖像功能之后如下：

相關自定義繪制類代碼如下：

 1fromPyQt5importQtWidgets
 2fromPyQt5importQtGui
 3fromPyQt5importQtCore
 4importsys
 5
 6
 7classMyCustomCanvas(QtWidgets.QWidget):
 8def__init__(self):
 9super().__init__()
10print("createmycustomcanvas")
11
12defpaintEvent(self,event):
13painter=QtGui.QPainter(self)
14#設置為反鋸齒
15painter.setRenderHint(QtGui.QPainter.Antialiasing)
16
17#填充黑色背景
18painter.fillRect(self.rect(),QtCore.Qt.black)
19
20#繪制圖像
21pic=QtGui.QPixmap("test3.png")
22painter.drawPixmap(self.rect(),pic)
23
24#設置字體與顏色，繪制文本
25pen=QtGui.QPen(QtCore.Qt.green,5,QtCore.Qt.DashLine)
26painter.setPen(pen)
27font=QtGui.QFont()
28font.setBold(True)
29font.setPointSizeF(24)
30painter.setFont(font)
31painter.drawText(QtCore.QPoint(20,50),"OpenCV學堂")
32
33#5表示線寬
34pen=QtGui.QPen(QtCore.Qt.red,5,QtCore.Qt.DashLine)
35painter.setPen(pen)
36painter.drawLine(50,100,50,400)
37
38#繪制矩形
39pen=QtGui.QPen(QtCore.Qt.yellow,5,QtCore.Qt.DotLine)
40painter.setPen(pen)
41painter.drawRect(QtCore.QRect(100,100,200,200))
42painter.fillRect(100,100,200,200,QtCore.Qt.green)
43
44#繪制圓
45pen=QtGui.QPen(QtCore.Qt.red,5,QtCore.Qt.DotLine)
46painter.setPen(pen)
47
48#設置為填充模式
49painter.setBrush(QtGui.QBrush(QtCore.Qt.yellow,QtCore.Qt.SolidPattern))
50
51#直接繪制
52painter.drawEllipse(QtCore.QRect(300,300,150,150))
53
54#貝塞爾曲線
55painter.setBrush(QtGui.QBrush(QtCore.Qt.red,QtCore.Qt.SolidPattern))
56self.drawBezierCurve(painter)
57
58defdrawBezierCurve(self,qp):
59path=QtGui.QPainterPath()
60path.moveTo(450,100)
61path.cubicTo(450,100,550,200,450,350)
62qp.drawPath(path)

審核編輯：劉清