在特定时间内完成绘制圆圈

Question

我正在尝试用圆圈创建倒计时.该圆圈将显示与给定的时间量相比已经过了多少时间.因此,如果倒计时是10秒并且已经过了5,那么将绘制半圈.我想出了这段代码:

from math import pi
import pygame


pygame.init()

(x, y) = (800, 600)
screen = pygame.display.set_mode((x, y))
clock = pygame.time.Clock()

radius = 50
# Just to place the circle in the center later on
top_left_corner = ((x / 2) - (radius / 2), (y / 2) - (radius / 2))
outer_rect = pygame.Rect(top_left_corner, (radius, radius))

countdown = 1000  # seconds

angle_per_frame = 2 * pi / (countdown * 60)
angle_drawn = 0
new_angle = angle_per_frame
while True:
    if angle_drawn < 2 * pi:
        new_angle += angle_drawn + angle_per_frame
        pygame.draw.arc(screen, (255, 255, 255), outer_rect, angle_drawn, new_angle, 10)
        angle_drawn += angle_per_frame
    clock.tick(60)
    pygame.display.update(outer_rect)

因此fps = 60,在我画的每一帧中2 * pi / countdown * fps,将一个完整的圆分成帧.然后在每个框架中,绘制圆的一部分.它似乎画圆圈很好,但它不能用于计时器有两个原因:

1. 圆圈似乎在比给定的更短的时间内完成.

2. 绘制圆圈时,似乎圆圈的最后部分绘制得更快.

谁能指出我做错了什么？

Answer 1

问题是你增加了new_angle和angle_drawn + angle_per_frame，因为你添加angle_per_frame的angle_drawn每一帧都会更大。

我宁愿使用clock.tick返回的增量时间，否则如果帧速率不恒定，可能会出现不准确的情况。然后将该angle_per_second值乘以dt以获得该帧的正确值。

另外，因为pygame.draw.arc如果角度之间的差异太小则不起作用，所以我必须从起始角度减去 0.2，并且必须在绘图开始之前添加短暂的延迟。

from math import pi
import pygame
from pygame import freetype


pygame.init()

x, y = 800, 600
screen = pygame.display.set_mode((x, y))
clock = pygame.time.Clock()
FONT = freetype.Font(None, 32)
WHITE = pygame.Color('white')

radius = 50
# Just to place the circle in the center later on
top_left_corner = (x/2 - radius/2, y/2 - radius/2)
outer_rect = pygame.Rect(top_left_corner, (radius, radius))

countdown = 10  # seconds
angle_per_second = 2*pi / countdown
angle = 0
dt = 0  # dt is the time since the last clock.tick call in seconds.
time = 0

done = False
while not done:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            done = True

    time += dt
    angle += angle_per_second * dt
    # Delay the drawing a little bit, because draw.arc doesn't work
    # with very small angle differences.
    if angle > 0.2:
        pygame.draw.arc(screen, WHITE, outer_rect, angle-0.2, angle, 10)

    rect = pygame.draw.rect(screen, (50, 50, 50), (400, 340, 100, 50))
    FONT.render_to(screen, (410, 350), str(round(time, 2)), WHITE)
    dt = clock.tick(60) / 1000  # / 1000 to convert it to seconds.
    pygame.display.update([outer_rect, rect])