Bartłomiej 'furas' Burek
furas.pl
# prywatne notatki - Python, Linux, Machine Learning, etc.

PyGame: Drag object on screen using mouse

First you have to create some object to drag and variable which will keep information if object is draged

rectangle = pygame.rect.Rect(176, 134, 30, 30)
rectangle_draging = False

You have to use

MOUSEBUTTONDOWN to check if object was clicked and set drag = True and remember offset between mouse position and rectangle top-left corner.

    elif event.type == pygame.MOUSEBUTTONDOWN:
        if event.button == 1:            
            if rectangle.collidepoint(event.pos):
                rectangle_draging = True
                mouse_x, mouse_y = event.pos
                offset_x = rectangle.x - mouse_x
                offset_y = rectangle.y - mouse_y

MOUSEBUTTONUP to set drag = False

    elif event.type == pygame.MOUSEBUTTONUP:
        if event.button == 1:            
            rectangle_draging = False

MOUSEMOTION to move object when drag == True using mouse position and offset.

    elif event.type == pygame.MOUSEMOTION:
        if rectangle_draging:
            mouse_x, mouse_y = event.pos
            rectangle.x = mouse_x + offset_x
            rectangle.y = mouse_y + offset_y

Working example

import pygame

# --- constants --- (UPPER_CASE names)

SCREEN_WIDTH = 430
SCREEN_HEIGHT = 410
WHITE = (255, 255, 255)
RED   = (255,   0,   0)
FPS = 30

# --- main ---

# - init -

pygame.init()
screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))

# - objects -

rectangle = pygame.rect.Rect(176, 134, 30, 30)
rectangle_draging = False

# - mainloop -

clock = pygame.time.Clock()

running = True

while running:

    # - events -

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

        elif event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 1:            
                if rectangle.collidepoint(event.pos):
                    rectangle_draging = True
                    mouse_x, mouse_y = event.pos
                    offset_x = rectangle.x - mouse_x
                    offset_y = rectangle.y - mouse_y

        elif event.type == pygame.MOUSEBUTTONUP:
            if event.button == 1:            
                rectangle_draging = False

        elif event.type == pygame.MOUSEMOTION:
            if rectangle_draging:
                mouse_x, mouse_y = event.pos
                rectangle.x = mouse_x + offset_x
                rectangle.y = mouse_y + offset_y

    # - draws (without updates) -

    screen.fill(WHITE)
    pygame.draw.rect(screen, RED, rectangle)
    pygame.display.flip()

    # - constant game speed / FPS -

    clock.tick(FPS)

# - end -

pygame.quit()

Other examples with many rectangles or circles and buttons on GitHub: furas/python-examples/pygame/drag-rectangles-circles

https://stackoverflow.com/questions/41332861/click-and-drag-a-rectangle-with-pygame

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