如何在pygame中连续旋转三角形？

Question

I am trying to use a gradient to change the color of a triangle and at the same time rotate it at regular intervals. This is my code. There seems to be a problem with clearing the surface as the previous output does not get cleared and the gradient flow effect is only visible for the first triangle.

import pygame, sys
import time
import random
from pygame.locals import *

pygame.init()
DISPLAYSURF = pygame.display.set_mode((500, 500), 0, 32)
pygame.display.set_caption('Drawing')
t = 0
i = 0
d = 0

# set up the colors
WHITE = (255,255,255)
GREEN = ((113, 201, 106),(98, 187, 91),(84, 174, 77),(69, 160, 63),(54, 147, 49),(40, 134, 35))

# draw on the surface object
DISPLAYSURF.fill(WHITE)
newSurf = pygame.transform.rotate(DISPLAYSURF, d)
pygame.draw.polygon(newSurf,GREEN[i],((250,70),(400,300),(100,300)))

t = 0.2
while True:
    DISPLAYSURF.fill(WHITE)
    DISPLAYSURF.blit(newSurf, (0,0,))
    pygame.display.update()
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
    if i==5:
        f = 0
        d = -90
        newSurf = pygame.transform.rotate(DISPLAYSURF, d)
        time.sleep(0.4)
    if i==0:
        f = 1
    if f==1:
        i = i+1
    else:
        i = i-1
    pygame.draw.polygon(newSurf,GREEN[i],((250,70),(400,300),(100,300)))
    time.sleep(t)

Since the output is an animation, I cannot post it here. Instead I am posting a couple of screenshots-

Answer 1

What you basically do in your loop is filling the canvas with white, drawing a triangle on it from newSurf and drawing a new triangle on newSurf at the exact same place with a different color.

After some iterations (when i == 5 and the green is the darkest) you rotate newSurf without clearing it and drawing a new triangle on it, changing its color for a few times and looping again and again.

What you want to do might involve multiple things but I'll go with the fact that you want to change the triangle color while rotating it: you need to rotate the canvas each frame and clearing it before drawing the triangle.

An other issue is that you rotate your newSurf before drawing on it, making the rotation useless. You only see something moving in the background because you do not clean newSurf before the drawing.

Last but not least, your code only works because you're rotating a square surface by 90 degrees each time. Thus not modifying its size. If you were to choose an other value, your newSurf would quickly grow too large for your memory.

import pygame, sys
import time
import random
from pygame.locals import *

pygame.init()
DISPLAYSURF = pygame.display.set_mode((500, 500), 0, 32)
pygame.display.set_caption('Drawing')
i = 0
d = 20 # change it to your liking
step = 1

# set up the colors
WHITE = (255,255,255)
TRANSPARENT = WHITE + (0,)
GREEN = ((113, 201, 106),(98, 187, 91),(84, 174, 77),(69, 160, 63),(54, 147, 49),(40, 134, 35))
newSurf = DISPLAYSURF.copy()
newSurf.fill(TRANSPARENT)

while True:
    DISPLAYSURF.fill(WHITE)
    triangle = newSurf.copy() # reset the surface to draw triangle on
    pygame.draw.polygon(triangle, GREEN[i],((250,70),(400,300),(100,300))) # draw the triangle on an unrotated surface
    triangle = pygame.transform.rotate(DISPLAYSURF, d*i)
    # since the rotation will likely enlarge the image, compute the position of the top-left corner relative to the rotated image
    width, height = triangle.get_size()
    width = (500-width)/2 # change 500 with DISPLAYSURF.get_size()[0] if you plan on changing the size
    height = (500-height)/2 # change 500 with DISPLAYSURF.get_size()[1] if you plan on changing the size
    DISPLAYSURF.blit(triangle, (width, height))
    pygame.display.update()
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
    i += step
    if not (i % 5):
        step = -step
    time.sleep(0.2)

You can also achieve a continuous rotation (in opposition to the back-and-forth presented here) using GREEN[i%5] and changing

i += step
if not (i % 5):
    step = -step

by i += 1