如何在Python中慢慢画一条线

Question

我想在python中慢慢画一条线，这样肉眼实际上就可以看到绘画的行为。

我尝试通过将其循环放置并每次都增加距离来进行制造，但从未成功。事情是什么都不会出现3秒钟，然后整个行将出现，这与我想要完成的相反。我在pygame.display.delay()函数上也没有成功。唯一可行的方法是将clock.tick设置为一些糟糕的值，例如，clock.tick(300000)但这只会使整个程序真正滞后。

def draw_red_line(i):
    y = 0
    while y < 300:
        pygame.draw.line(screen, RED, (i*100+50, 0), (i*100+50, y))
        y+=0.01

Answer 1

在这种情况下，使用睡眠不是一个好主意，因为它会使整个线程（即单线程模型中的整个程序）变慢。

最好保留有关线路的某种状态信息，并根据实时时间（例如经过的毫秒数）逐秒处理线路的“增长”。

这意味着需要将线分成多个段，最小的线段是单个像素。使用中点线算法是确定一条线上所有像素的有效方法。一旦确定了所有“线部分”，就可以根据经过的时间简单地更新线的终点。

这是我之前编写的一些代码，给定一对点，它们返回一个像素列表。

midpoint.py：

def __plotLineLow( x0,y0, x1,y1 ):
    points = []
    dx = x1 - x0
    dy = y1 - y0
    yi = 1
    if dy < 0:
        yi = -1
        dy = -dy
    D = 2*dy - dx
    y = y0

    for x in range( x0, x1 ):
        points.append( (x,y) )
        if D > 0:
           y = y + yi
           D = D - 2*dx
        D = D + 2*dy
    return points

def __plotLineHigh( x0,y0, x1,y1 ):
    points = []
    dx = x1 - x0
    dy = y1 - y0
    xi = 1
    if dx < 0:
        xi = -1
        dx = -dx
    D = 2*dx - dy
    x = x0

    for y in range( y0, y1 ):
        points.append( (x,y) )
        if D > 0:
            x = x + xi
            D = D - 2*dy
        D = D + 2*dx
    return points

def linePoints( pointA, pointB ):
    """ Generate a list of integer points on the line pointA -> pointB """
    x0, y0 = pointA
    x1, y1 = pointB
    points = []
    if ( abs(y1 - y0) < abs(x1 - x0) ):
        if ( x0 > x1 ):
            points += __plotLineLow( x1, y1, x0, y0 )
        else:
            points += __plotLineLow( x0, y0, x1, y1 )
    else:
        if ( y0 > y1 ):
            points += __plotLineHigh( x1, y1, x0, y0 )
        else:
            points += __plotLineHigh( x0, y0, x1, y1 )

    return points


if __name__ == "__main__":
    #midPoint( (597, 337), (553, 337) )
    print( str( linePoints( (135, 295), (135, 304) ) ) )

以及一些实现SlowLine类的演示代码。

import pygame
import random
import time
import sys

from midpoint import linePoints  # Midpoint line algorithm

# Window size
WINDOW_WIDTH      = 400
WINDOW_HEIGHT     = 400

SKY_BLUE = ( 30,  30,  30)
SKY_RED  = (200, 212,  14)

# Global millisecond count since start
NOW_MS = 0

class SlowLine():
    def __init__( self, pixels_per_second, x0,y0, x1,y1, colour=SKY_RED ):
        self.points       = linePoints( ( x0, y0 ), ( x1, y1 ) )
        self.pixel_count  = len( self.points )
        self.speed        = pixels_per_second
        self.start_point  = self.points[0]     # start with a single-pixel line
        self.end_point    = self.points[0]
        self.pixel_cursor = 0                  # The current end-pixel
        self.last_update  = 0                  # Last time we updated
        self.colour       = colour
        self.fully_drawn  = False

    def update(self):
        global NOW_MS

        if ( self.fully_drawn == True ):
            # nothing to do
            pass
        else:
            # How many milliseconds since the last update() call?
            if ( self.last_update == 0 ):
                self.last_update = NOW_MS
                time_delta = 0
            else:
                time_delta = NOW_MS - self.last_update
                self.last_udpate = NOW_MS

            # New pixels to add => speed * time
            new_pixel_count = time_delta * self.speed / 1000   # this may loose precision with very small speeds

            if ( new_pixel_count + self.pixel_cursor > self.pixel_count ):
                # We're out of pixels
                self.end_point  = self.points[-1]   
                self.full_drawn = True
            else:
                # Grow the line by <new_pixel_count> pixels
                self.pixel_cursor += new_pixel_count
                self.end_point     = self.points[ int( self.pixel_cursor ) ]

    def draw( self, screen ):
        pygame.draw.line( screen, self.colour, self.start_point, self.end_point )




### MAIN
pygame.init()
SURFACE = pygame.HWSURFACE|pygame.DOUBLEBUF|pygame.RESIZABLE
WINDOW  = pygame.display.set_mode( ( WINDOW_WIDTH, WINDOW_HEIGHT ), SURFACE )
pygame.display.set_caption("Slow Line Movement")


# Create some random lines
lines = []
for i in range( 20 ):
    rand_speed = random.randint( 1, 50 )
    rand_x0    = random.randint( 0, WINDOW_WIDTH )
    rand_y0    = random.randint( 0, WINDOW_HEIGHT )
    rand_x1    = random.randint( 0, WINDOW_WIDTH )
    rand_y1    = random.randint( 0, WINDOW_HEIGHT )
    lines.append( SlowLine( rand_speed, rand_x0, rand_y0, rand_x1, rand_y1 ) )


# Main event loop
clock = pygame.time.Clock()
done = False
while not done:
    NOW_MS = pygame.time.get_ticks()

    # Update the line lengths
    for l in lines:
        l.update()

    # Handle user-input
    for event in pygame.event.get():
        if ( event.type == pygame.QUIT ):
            done = True

    # Movement keys
    keys = pygame.key.get_pressed()
    if ( keys[pygame.K_UP] ):
        print("up")
    elif ( keys[pygame.K_DOWN] ):
        print("down")
    elif ( keys[pygame.K_LEFT] ):
        print("left")
    elif ( keys[pygame.K_RIGHT] ):
        print("right")
    elif ( keys[pygame.K_q] and ( keys[pygame.K_RCTRL] or keys[pygame.K_LCTRL] ) ):
        print("^Q")
        done = True

    # Update the window, but not more than 60fps
    WINDOW.fill( SKY_BLUE )
    for l in lines:
        l.draw( WINDOW )

    pygame.display.flip()

    # Clamp FPS
    clock.tick_busy_loop(60)

pygame.quit()

在此动画中，进度有点生涩，但这是动画，而不是演示。