Making Label Jump using PyQt5 in Python

Last Updated : 01 Aug, 2020

Prerequisite: Introduction to PyQt5

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.

NOw, we will see how we can make the label jump. Sometimes there is a need to make the label jump while designing 2-D games in PyQt5, Jumping label is a label which when pressed jump key(here space bar) goes up and its speed of going up decreases and when it attains the maximum height, it starts going down with the increase in speed. Speed decreases while going up and decreases while going down it due to the gravity effect.

Concept : We can make the label jump by changing its Y co-ordinate with the time, we can get the Y co-ordinate for each time with the help of basic formula from classical mechanics i.e given below :

Force = 1/2 * mass * velocity^2

By decrementing this force value from the initial Y co-ordinate will give us the new Y co-ordinate for each time and then decrementing the speed.

Implementation Steps :

1. Create a main window.
2. Create a jump flag, and a speed and mass variable.
3. Create a label.
4. Set label geometry and the style sheet.
5. Override the key press event.
6. Inside the key press event check when the space bar key is pressed.
7. If space bar key is pressed make the jump variable true.
8. Create a timer object and add action to the timer which get called after every 50 milliseconds.
9. Inside the timer action get the Y co-ordinate of the label and check if the jump flag is true.
10. If jump flag is true calculate the force and decrement the force value from the Y co-ordinate and set the new position to the label.
11. If the speed becomes zero make the mass negative, and if the label comes back to normal position make the jump flag false and reset the value of mass and speed.

Below is the implementation :

Python3

# importing required libraries 
from PyQt5.QtWidgets import *
from PyQt5 import QtCore, QtGui 
from PyQt5.QtGui import *
from PyQt5.QtCore import *
  
import sys 
  
# Window class 
class Window(QMainWindow): 
  
    def __init__(self): 
        super().__init__() 
  
        # setting title 
        self.setWindowTitle("Python ") 
  
        # width of window 
        self.w_width = 500
  
        # height of window 
        self.w_height = 500
  
        # setting geometry 
        self.setGeometry(100, 100,  
                         self.w_width, self.w_height) 
  
        # calling method 
        self.UiComponents() 
  
        # showing all the widgets 
        self.show() 
  
        # speed variable 
        self.speed = 5
  
        self.mass = 1
  
        # jump flag 
        self.jump = False
  
    # method for components 
    def UiComponents(self): 
  
        # creating a label 
        self.label = QLabel(self) 
  
        # label width 
        self.l_width = 40
  
        # label height 
        self.l_height = 40
  
        # setting geometry to the label 
        self.label.setGeometry(200, 200,  
                               self.l_width, 
                               self.l_height) 
  
        # setting stylesheet to the label 
        self.label.setStyleSheet("QLabel"
                                 "{"
                                 "border : 4px solid darkgreen;"
                                 "background : lightgreen;"
                                 "}") 
  
  
        # creating a timer object 
        timer = QTimer(self) 
  
        # setting timer start time 
        timer.start(50) 
  
        # adding action to the timer 
        timer.timeout.connect(self.show_time) 
  
  
    # method called by the timer 
    def show_time(self): 
  
        # checking jump flag 
        if self.jump: 
  
            y = self.label.y() 
  
            # calculate force (F).  
            # F = 1 / 2 * mass * velocity ^ 2. 
            # here we are not using  ( 1/2 ) 
            Force = self.mass * (self.speed ** 2) 
  
            # change in the y co-ordinate 
            y -= Force 
  
            self.label.move(200, y) 
  
            # decreasing velocity while going up  
            # and become negative while coming down 
            self.speed = self.speed - 1
  
            # object reached its maximum height 
            if self.speed < 0: 
                # negative sign is added to  
                # counter negative velocity 
                self.mass = -1
  
            # objected reaches its original state 
            if self.speed == -6: 
                # making jump equal to false 
                self.jump = False
  
                # setting original values to  
                # speed  and mass 
                self.speed = 5
                self.mass = 1
  
    # override the key press event 
    def keyPressEvent(self, event): 
        
       # if space bar is pressed 
       if event.key() == Qt.Key_Space: 
          
           # make the jump flag true 
           self.jump = True
  
  
  
# create pyqt5 app 
App = QApplication(sys.argv) 
  
# create the instance of our Window 
window = Window() 
  
# start the app 
sys.exit(App.exec()) 