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

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 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: