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 :
- User can select different brush sizes
- User can select different brush color
- Saving of the canvas
- 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
# 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 wwindow window.show() # start the app sys.exit(App.exec()) |
Output :
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