Usage and Precautions of QPainter in QT

# Introduction

In QT, QPainter is an essential tool for performing drawing operations on QWidget and its subclasses. With QPainter, we can implement the drawing of various graphics, text display, and advanced drawing techniques. In this article, we will introduce the usage and precautions of QPainter in QT, to help readers better master this drawing tool.

# Initialization and Basic Drawing of QPainter

When drawing with QT, a QPainter object must first be created, and various graphics are drawn through this object. The following will introduce how to initialize the QPainter object and draw some basic graphics.

### Creating QPainter Object

Before drawing, you need to obtain a drawing device, usually a QWidget or QPixmap. Then, create a QPainter object in the paintEvent() function to perform the drawing operation.

# Creating QPainter object in paintEvent() function
def paintEvent(self, event):
    painter = QPainter(self)
    painter.begin(self)
    # Drawing content
    painter.end()

### Drawing Basic Shapes

With the created QPainter object, it is very convenient to draw various basic shapes, such as lines, rectangles, and ellipses.

# Drawing a line
painter.drawLine(10, 10, 100, 100)

# Drawing a rectangle
rect = QRect(50, 50, 100, 100)
painter.drawRect(rect)

# Drawing an ellipse
ellipse = QRect(150, 150, 100, 50)
painter.drawEllipse(ellipse)

Through the above code examples, we can achieve the drawing of basic shapes with the QPainter object in QT.

# Setting Up Brushes and Pens in QPainter

When using QPainter for drawing, we often need to set the properties of the brush (fill) and the pen (outline) to achieve different graphical effects. The following will introduce how to set up the relevant properties of brushes and pens.

1. **Setting the brush color and fill pattern**

brush = QBrush(Qt.red, Qt.SolidPattern)   # Creating a red solid brush
painter.setBrush(brush)   # Setting the brush

The above code creates a red solid brush and sets it as the current painter's brush. Here, `Qt.SolidPattern` represents the solid fill pattern, and you can choose different fill patterns according to your needs.

2. **Setting the pen color, width, and style**

pen = QPen(Qt.blue, 2, Qt.DashLine)   # Creating a blue dashed pen with a width of 2
painter.setPen(pen)   # Setting the pen

The above code creates a blue dashed pen with a width of 2 and sets it as the current painter's pen. You can set pens with different colors, widths, and styles to draw various border