PyQt5 – Create Paint Application

There are so many options provided by Python to develop GUI application and PyQt5 is one of them. PyQt5 is cross-platform GUI toolkit, a set of python bindings for Qt v5. One can develop an interactive desktop application with so much ease because of the tools and simplicity provided by this library.

In this article we will see how we can create a Paint application using PyQt5. Our Paint application will consist of following

 Features :

1. User can select different brush sizes 
2. User can select different brush color 
3. Saving of the canvas 
4. Clearing the whole canvas at once  

Steps for designing the widgets –
1. Create a window sets its geometry and title 
2. Create menu bar 
3. Inside menu bar add different menus, that are file menu, size menu and color menu 
4. Add save and clear action to the file menu 

5. Add different brush sizes action to the brush size menu 

6. Add different brush color action to the brush color menu 

7. Create a white canvas and add it to the window

Back-end steps :
1. Create different variable : Drawing flag to check if currently drawing or not and set it to False, brush size variable to set current brush size,     brush color to set current brush color and current position variable to know position of cursor 
2. Add action to the clear and save widget 
3. Inside clear action fill the canvas with white color 
4. Inside the save action save the canvas 
5. Add actions(methods) to various brush sizes and color to set size and color 
6. Create paint event to draw white canvas on the screen 
7. Create method to know when mouse left button is pressed inside that method make drawing flag true and change the current position 
8. Create method for mouse movement, inside this method check if drawing flag is true and button is still pressed then draw using painter     object and change the position according. 
9. Create a method to know mouse button is released inside this method make drawing flag to false.

Below is the implementation 

Python3

# importing libraries
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *
import sys

# window class
class Window(QMainWindow):
    def __init__(self):
        super().__init__()

        # setting title
        self.setWindowTitle("Paint with PyQt5")

        # setting geometry to main window
        self.setGeometry(100, 100, 800, 600)

        # creating image object
        self.image = QImage(self.size(), QImage.Format_RGB32)

        # making image color to white
        self.image.fill(Qt.white)

        # variables
        # drawing flag
        self.drawing = False
        # default brush size
        self.brushSize = 2
        # default color
        self.brushColor = Qt.black

        # QPoint object to tract the point
        self.lastPoint = QPoint()

        # creating menu bar
        mainMenu = self.menuBar()

        # creating file menu for save and clear action
        fileMenu = mainMenu.addMenu("File")

        # adding brush size to main menu
        b_size = mainMenu.addMenu("Brush Size")

        # adding brush color to ain menu
        b_color = mainMenu.addMenu("Brush Color")

        # creating save action
        saveAction = QAction("Save", self)
        # adding short cut for save action
        saveAction.setShortcut("Ctrl + S")
        # adding save to the file menu
        fileMenu.addAction(saveAction)
        # adding action to the save
        saveAction.triggered.connect(self.save)

        # creating clear action
        clearAction = QAction("Clear", self)
        # adding short cut to the clear action
        clearAction.setShortcut("Ctrl + C")
        # adding clear to the file menu
        fileMenu.addAction(clearAction)
        # adding action to the clear
        clearAction.triggered.connect(self.clear)

        # creating options for brush sizes
        # creating action for selecting pixel of 4px
        pix_4 = QAction("4px", self)
        # adding this action to the brush size
        b_size.addAction(pix_4)
        # adding method to this
        pix_4.triggered.connect(self.Pixel_4)

        # similarly repeating above steps for different sizes
        pix_7 = QAction("7px", self)
        b_size.addAction(pix_7)
        pix_7.triggered.connect(self.Pixel_7)

        pix_9 = QAction("9px", self)
        b_size.addAction(pix_9)
        pix_9.triggered.connect(self.Pixel_9)

        pix_12 = QAction("12px", self)
        b_size.addAction(pix_12)
        pix_12.triggered.connect(self.Pixel_12)

        # creating options for brush color
        # creating action for black color
        black = QAction("Black", self)
        # adding this action to the brush colors
        b_color.addAction(black)
        # adding methods to the black
        black.triggered.connect(self.blackColor)

        # similarly repeating above steps for different color
        white = QAction("White", self)
        b_color.addAction(white)
        white.triggered.connect(self.whiteColor)

        green = QAction("Green", self)
        b_color.addAction(green)
        green.triggered.connect(self.greenColor)

        yellow = QAction("Yellow", self)
        b_color.addAction(yellow)
        yellow.triggered.connect(self.yellowColor)

        red = QAction("Red", self)
        b_color.addAction(red)
        red.triggered.connect(self.redColor)


    # method for checking mouse cicks
    def mousePressEvent(self, event):

        # if left mouse button is pressed
        if event.button() == Qt.LeftButton:
            # make drawing flag true
            self.drawing = True
            # make last point to the point of cursor
            self.lastPoint = event.pos()

    # method for tracking mouse activity
    def mouseMoveEvent(self, event):

        # checking if left button is pressed and drawing flag is true
        if (event.buttons() & Qt.LeftButton) & self.drawing:

            # creating painter object
            painter = QPainter(self.image)

            # set the pen of the painter
            painter.setPen(QPen(self.brushColor, self.brushSize,
                            Qt.SolidLine, Qt.RoundCap, Qt.RoundJoin))

            # draw line from the last point of cursor to the current point
            # this will draw only one step
            painter.drawLine(self.lastPoint, event.pos())

            # change the last point
            self.lastPoint = event.pos()
            # update
            self.update()

    # method for mouse left button release
    def mouseReleaseEvent(self, event):

        if event.button() == Qt.LeftButton:
            # make drawing flag false
            self.drawing = False

    # paint event
    def paintEvent(self, event):
        # create a canvas
        canvasPainter = QPainter(self)

        # draw rectangle  on the canvas
        canvasPainter.drawImage(self.rect(), self.image, self.image.rect())

    # method for saving canvas
    def save(self):
        filePath, _ = QFileDialog.getSaveFileName(self, "Save Image", "",
                          "PNG(*.png);;JPEG(*.jpg *.jpeg);;All Files(*.*) ")

        if filePath == "":
            return
        self.image.save(filePath)

    # method for clearing every thing on canvas
    def clear(self):
        # make the whole canvas white
        self.image.fill(Qt.white)
        # update
        self.update()

    # methods for changing pixel sizes
    def Pixel_4(self):
        self.brushSize = 4

    def Pixel_7(self):
        self.brushSize = 7

    def Pixel_9(self):
        self.brushSize = 9

    def Pixel_12(self):
        self.brushSize = 12

    # methods for changing brush color
    def blackColor(self):
        self.brushColor = Qt.black

    def whiteColor(self):
        self.brushColor = Qt.white

    def greenColor(self):
        self.brushColor = Qt.green

    def yellowColor(self):
        self.brushColor = Qt.yellow

    def redColor(self):
        self.brushColor = Qt.red



# create pyqt5 app
App = QApplication(sys.argv)

# create the instance of our Window
window = Window()

# showing the window
window.show()

# start the app
sys.exit(App.exec())

Output :