How to use the mouse to scale and rotate an image in PyGame ?

Last Updated : 28 Apr, 2021

In this article, we will discuss how to transform the image i.e (scaling and rotating images) using the mouse in Pygame.

Approach

Step 1: First, import the libraries Pygame and math.

import pygame  import math  from pygame.locals import *

Step 2: Now, take the colors as input that we want to use in the game.

color_1 = #RGB value of color 1  color_2 = #RGB value of color 2  color_n = #RGB value of color n

Step 3: Then, initialize the constructor

pygame.init()

Step 4: Set the dimensions of your GUI game.

w, h = #Width dimension, #Height dimension  screen = pygame.display.set_mode((w, h))

Step 5: Set the running value for running the game, the angle by which it can be moved.

running = True  angle = 0  scale = 1

Step 6: Next, take the image as input which we want to move with the mouse

img_logo = pygame.image.load('#Enter the image url')  img_logo.convert()

Step 7: Draw a border around an image.

rect_logo = img_logo.get_rect()  pygame.draw.rect(img_logo, color_1, rect_logo, 1)

Step 8: Locate the center of the GUI game and get the position of the mouse.

center = w//2, h//2  mouse = pygame.mouse.get_pos()

Step 9: Store the image in a new variable and construct a rectangle around the image.

img = img_logo  rect = img.get_rect()  rect.center = center

Step 10: Set the things which you want your app to do when in running state.

while running:      for event in pygame.event.get():

Step 10.1: Once the app is in a running state, make it quit if the user wants to quit.

        if event.type == QUIT:              running = False

Step 10.2: In case, the user doesn't want to quit, set at what angle the image should rotate.

        if event.type == KEYDOWN:              if event.key == K_ra:                  if event.mod & KMOD_SHIFT:                                        # angle at which it should move left                      angle -=                   else:                                        # angle at which it should move right                      angle +=

Step 10.3: Also, set at what ratio the image size should decrease or increase.

            elif event.key == K_sa:                  if event.mod & KMOD_SHIFT:                      scale /= #scale at which the image size should decrease                  else:                      scale *= #scale at which the image size should increase

Step 10.4: Set at what coordinates, angle, and scale the image will rotate or resize.

        elif event.type == MOUSEMOTION:

Step 10.4.1: Store the current position of the event in the new variable.

            mouse = event.pos

Step 10.4.2: Locate the Cartesian coordinates with the help of the mouse variable and center of the image for rotating the image..

            x = mouse[0] - center[0]              y = mouse[1] - center[1]

Step 10.4.3: Further, calculate the distance between the two points (0,0) and (x, y) with the help of formula √x²+y²

            d = math.sqrt(x ** 2 + y ** 2)

Step 10.4.4: Now, calculate the angle in degrees at which the image should rotate using the Python method math.atan2() which returns the arctangent of y/x, in radians.

            angle = math.degrees(-math.atan2(y, x))

Step 10.4.5: Calculate which scale the image size should decrease or increase using the function abs, which returns the magnitude of the number.

            scale = abs(5 * d / w)

Step 10.4.6: Calculate the updated position of the image in the running state using the rotozoom function which is a combined scale and rotation transform.

            img = pygame.transform.rotozoom(img_logo, angle, scale)

Step 10.4.7: Construct the rectangle around the updated image

            rect = img.get_rect()              rect.center = center

Step 11: Next, you need to set the screen color and the image on the screen.

    screen.fill(color_3)      screen.blit(img, rect)

Step 12: Later on, draw the rectangle, line, and circles which will help in moving the image.

    pygame.draw.rect(screen, color_2, rect, #thickness of rectangle)      pygame.draw.line(screen, color_3, center, mouse, #Thickness of line)      pygame.draw.circle(screen, color_1, center, #radius of circle, #thickness of circumference)      pygame.draw.circle(screen, color_2, mouse, #radius of circle, #thickness of circumference)

Step 13: Furthermore, update the changes done in the GUI game.

  pygame.display.update()

Step 14: Finally, quit the GUI game.

pygame.quit()

Below is the implementation.

Python

# Python program to transform the  # image with the mouse  #Import the libraries pygame and math import pygame import math from pygame.locals import *  # Take colors input RED = (255, 0, 0) BLACK = (0, 0, 0) YELLOW = (255, 255, 0)  #Construct the GUI game pygame.init()  #Set dimensions of game GUI w, h = 600, 440 screen = pygame.display.set_mode((w, h))  # Set running, angle and scale values running = True angle = 0 scale = 1  # Take image as input img_logo = pygame.image.load('gfg_image.jpg') img_logo.convert()  # Draw a rectangle around the image rect_logo = img_logo.get_rect() pygame.draw.rect(img_logo, RED, rect_logo, 1)  # Set the center and mouse position center = w//2, h//2 mouse = pygame.mouse.get_pos()  #Store the image in a new variable #Construct the rectangle around image img = img_logo rect = img.get_rect() rect.center = center  # Setting what happens when game is # in running state while running:     for event in pygame.event.get():          # Close if the user quits the game         if event.type == QUIT:             running = False          # Set at which angle the image will         # move left or right         if event.type == KEYDOWN:             if event.key == K_ra:                 if event.mod & KMOD_SHIFT:                     angle -= 5                 else:                     angle += 5              # Set at what ratio the image will             # decrease or increase             elif event.key == K_sa:                 if event.mod & KMOD_SHIFT:                     scale /= 1.5                 else:                     scale *= 1.5                          # Move the image with the specified coordinates,         # angle and scale                 elif event.type == MOUSEMOTION:             mouse = event.pos             x = mouse[0] - center[0]             y = mouse[1] - center[1]             d = math.sqrt(x ** 2 + y ** 2)             angle = math.degrees(-math.atan2(y, x))             scale = abs(5 * d / w)             img = pygame.transform.rotozoom(img_logo, angle, scale)             rect = img.get_rect()             rect.center = center          # Set screen color and image on screen     screen.fill(YELLOW)     screen.blit(img, rect)      # Draw the rectangle, line and circle through     # which image can be transformed      pygame.draw.rect(screen, BLACK, rect, 3)     pygame.draw.line(screen, RED, center, mouse, 2)     pygame.draw.circle(screen, RED, center, 6, 1)     pygame.draw.circle(screen, BLACK, mouse, 6, 2)          # Update the GUI game     pygame.display.update()  # Quit the GUI game pygame.quit()

Output:

How to create Buttons in a game using PyGame?

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How to use the mouse to scale and rotate an image in PyGame ?

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