Draw a transparent rectangles and polygons in pygame

Unfortunately there is no good way to draw a transparent shape. See pygame.draw module:

A color's alpha value will be written directly into the surface [...], but the draw function will not draw transparently.

Hence you need to do a workaround:

1. Create a pygame.Surface object with a per-pixel alpha format large enough to cover the shape.
2. Draw the shape on the _Surface.
3. Blend the Surface with the target Surface. blit() by default blends 2 Surfaces

For example 3 functions, which can draw transparent rectangles, circles and polygons:

def draw_rect_alpha(surface, color, rect):
    shape_surf = pygame.Surface(pygame.Rect(rect).size, pygame.SRCALPHA)
    pygame.draw.rect(shape_surf, color, shape_surf.get_rect())
    surface.blit(shape_surf, rect)

def draw_circle_alpha(surface, color, center, radius):
    target_rect = pygame.Rect(center, (0, 0)).inflate((radius * 2, radius * 2))
    shape_surf = pygame.Surface(target_rect.size, pygame.SRCALPHA)
    pygame.draw.circle(shape_surf, color, (radius, radius), radius)
    surface.blit(shape_surf, target_rect)

def draw_polygon_alpha(surface, color, points):
    lx, ly = zip(*points)
    min_x, min_y, max_x, max_y = min(lx), min(ly), max(lx), max(ly)
    target_rect = pygame.Rect(min_x, min_y, max_x - min_x, max_y - min_y)
    shape_surf = pygame.Surface(target_rect.size, pygame.SRCALPHA)
    pygame.draw.polygon(shape_surf, color, [(x - min_x, y - min_y) for x, y in points])
    surface.blit(shape_surf, target_rect)

Minimal example: repl.it/@Rabbid76/PyGame-TransparentShapes

import pygame

def draw_rect_alpha(surface, color, rect):
    shape_surf = pygame.Surface(pygame.Rect(rect).size, pygame.SRCALPHA)
    pygame.draw.rect(shape_surf, color, shape_surf.get_rect())
    surface.blit(shape_surf, rect)

def draw_circle_alpha(surface, color, center, radius):
    target_rect = pygame.Rect(center, (0, 0)).inflate((radius * 2, radius * 2))
    shape_surf = pygame.Surface(target_rect.size, pygame.SRCALPHA)
    pygame.draw.circle(shape_surf, color, (radius, radius), radius)
    surface.blit(shape_surf, target_rect)

def draw_polygon_alpha(surface, color, points):
    lx, ly = zip(*points)
    min_x, min_y, max_x, max_y = min(lx), min(ly), max(lx), max(ly)
    target_rect = pygame.Rect(min_x, min_y, max_x - min_x, max_y - min_y)
    shape_surf = pygame.Surface(target_rect.size, pygame.SRCALPHA)
    pygame.draw.polygon(shape_surf, color, [(x - min_x, y - min_y) for x, y in points])
    surface.blit(shape_surf, target_rect)

pygame.init()
window = pygame.display.set_mode((250, 250))
clock = pygame.time.Clock()

background = pygame.Surface(window.get_size())
ts, w, h, c1, c2 = 50, *window.get_size(), (160, 160, 160), (192, 192, 192)
tiles = [((x*ts, y*ts, ts, ts), c1 if (x+y) % 2 == 0 else c2) for x in range((w+ts-1)//ts) for y in range((h+ts-1)//ts)]
for rect, color in tiles:
    pygame.draw.rect(background, color, rect)

run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    window.blit(background, (0, 0))

    draw_rect_alpha(window, (0, 0, 255, 127), (55, 90, 140, 140))
    draw_circle_alpha(window, (255, 0, 0, 127), (150, 100), 80)
    draw_polygon_alpha(window, (255, 255, 0, 127), 
        [(100, 10), (100 + 0.8660 * 90, 145), (100 - 0.8660 * 90, 145)])

    pygame.display.flip()

pygame.quit()
exit()

the most i can do to help you is to show you how to draw a rectangle that is not filled in. the line for the rectangle is:

pygame.draw.rect(surface, [255, 0, 0], [50, 50, 90, 180], 1)

the "1" means that it is not filled in

A way to do this is to instead of drawing a rectangle with pygame, you could create an image of a transparent rectangle by using a drawing program such as paint.net or Fire Alpaca.