How does the collidepoint function in pygame work?

Question

So I am doing a lab regarding pong and I was lost on the concept of collidepoint a function in pygame, which checks whether the center of the circle is inside the paddle. Upon looking at documentation I was still confused since I am very new to programming and I am really having a hard time settling in and getting a grasp of the new skills thrown at me. I would really appreciate if someone could help me out by explaining it a bit more and maybe giving a basic simple example.

Answer 1

The point-collision is documented in the PyGame Rect class.

Essentially you pass a co-ordinate to pygame.Rect.collidepoint(), and it will return True if that point is within the bounds of the rectangle.

import pygame

# Window size
WINDOW_WIDTH=400
WINDOW_HEIGHT=400

pygame.init()
window = pygame.display.set_mode( ( WINDOW_WIDTH, WINDOW_HEIGHT ) )
pygame.display.set_caption("Point Collision")

BLACK = (  50,  50,  50 )
GREEN = (  34, 139,  34 )
BLUE  = ( 161, 255, 254 )

# The rectangle to click-in
# It is window-centred, and 33% the window size
click_rect  = pygame.Rect( WINDOW_WIDTH//3, WINDOW_HEIGHT//3, WINDOW_WIDTH//3, WINDOW_HEIGHT//3 )
rect_colour = BLACK

### Main Loop
clock = pygame.time.Clock()
done = False
while not done:

    # Handle all the events
    for event in pygame.event.get():
        if ( event.type == pygame.QUIT ):
            done = True

        elif ( event.type == pygame.MOUSEBUTTONUP ):
            mouse_position = pygame.mouse.get_pos()             # Location of the mouse-click
            if ( click_rect.collidepoint( mouse_position ) ):   # Was that click inside our rectangle 
                print( "hit" )
                # Flip the colour of the rect
                if ( rect_colour == BLACK ):
                    rect_colour = GREEN
                else:
                    rect_colour = BLACK
            else:
                print( "click-outside!" )

    # update the screen
    window.fill( BLUE )
    pygame.draw.rect( window, rect_colour, click_rect)  # DRAW OUR RECTANGLE
    pygame.display.flip()

    # Clamp the FPS to an upper-limit
    clock.tick_busy_loop( 60 )


pygame.quit()

Note the use of the collidepoint() in the lower half of the code:

if ( click_rect.collidepoint( mouse_position ) ):  

Here the code is checking that the co-ordinate recently discovered via a mouse-input event is within the click_rect (a pygame.Rect declared before the main loop). If the co-ordinates are within the rectangle, it is draw in a different colour.

The bulk of the code here is to simply open the window, and run the main input/update loop.