python – matplotlib – 直接在画布上绘图

发布时间：2020-12-20 13:41:01 所属栏目：Python 来源：网络整理

导读：由于动态更新的性能问题,我需要在画布上直接绘制很多矩形作为非常低的级别,也就是说不使用matplotlib.patches,因为我们必须使用经典的GUI. 更准确地说,我想只绘制一个矩形,而不仅仅是所有的图形. 可能吗？这是我使用Joe Kington给出的链接的测试代码. #!/u

由于动态更新的性能问题,我需要在画布上直接绘制很多矩形作为非常低的级别,也就是说不使用matplotlib.patches,因为我们必须使用经典的GUI.

更准确地说,我想只绘制一个矩形,而不仅仅是所有的图形.

可能吗？

这是我使用Joe Kington给出的链接的测试代码.

#!/usr/bin/env python3

from random import randint,choice
import time

import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
import matplotlib.colors as colors
import matplotlib

back_color = "black"
colors     = ['red','green','cyan','yellow']

width  = 16
height = 16

ax     = plt.subplot(111)
canvas = ax.figure.canvas

ax.set_xlim([0,width])
ax.set_ylim([0,height])

def update():
    global ax,canvas,colors,width,height

    x = randint(0,width - 1)
    y = randint(0,height - 1)

    rect = mpatches.Rectangle(
        (x,y),1,facecolor = choice(colors),edgecolor = back_color
    )

    start = time.time()
    ax.draw_artist(rect)
    canvas.blit(ax.bbox)
    print("draw >>>",time.time() - start)

timer = canvas.new_timer(interval = 1)
timer.add_callback(update)
timer.start()

plt.show()

在Mac O $下,我获得以下消息.

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/backend_bases.py",line 1203,in _on_timer
    ret = func(*args,**kwargs)
  File "/Users/xxx/test.py",line 86,in update
    ax.draw_artist(rect)
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/axes.py",line 2100,in draw_artist
    a.draw(self._cachedRenderer)
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/artist.py",line 56,in draw_wrapper
    draw(artist,renderer,*args,**kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/patches.py",line 393,in draw
    gc = renderer.new_gc()
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/site-packages/matplotlib/backends/backend_macosx.py",line 97,in new_gc
    self.gc.save()
RuntimeError: CGContextRef is NULL

对于Maverick用户

对于想要使用以下代码以及动画的Mac用户,我有一个好消息.我在没有任何软件的Mac上重新安装了Maverick OS,这称为干净安装,然后我安装了Anaconda和XQuark(see this).

要使动画有效,只需在任何其他matplotlib导入之前使用以下两行.

import matplotlib
matplotlib.use('TkAgg')

我认为这适用于Anaconda支持的任何Mac OS.只有Maverick才需要使用XQuark.

解决方法

您当前的代码有两个问题.

>你没有先画出画布而试图搞砸.你得到的错误是后端特定的,但基本上,它说的是画布的渲染器还没有被初始化.
>您没有将矩形艺术家添加到轴.因此,调用ax.draw_artist(rect)时不会被绘制.

这是一个有效的例子：

from random import randint,choice
import time
import matplotlib.pyplot as plt
import matplotlib.patches as mpatches

back_color = "black"
colors     = ['red','yellow']
width,height = 16,16

fig,ax = plt.subplots()
ax.set(xlim=[0,width],ylim=[0,height]) # Or use "ax.axis([x0,x1,y0,y1])"

# Be sure to draw the canvas once before we start blitting. Otherwise
# a) the renderer doesn't exist yet,and b) there's noting to blit onto
fig.canvas.draw()

def update():
    x = randint(0,edgecolor = back_color
    )
    ax.add_artist(rect)

    start = time.time()
    ax.draw_artist(rect)
    fig.canvas.blit(ax.bbox)
    print("draw >>>",time.time() - start)

timer = fig.canvas.new_timer(interval=1)
timer.add_callback(update)
timer.start()

plt.show()

但是,在这一点上,每次添加新艺术家都会更有意义.相反,添加初始矩形并每次更新它.例如：

from random import randint,'yellow']

width,y1])"

rect = mpatches.Rectangle(
    (0,0),edgecolor = back_color
)
ax.add_artist(rect)

# Be sure to draw the canvas once before we start blitting. Otherwise
# a) the renderer doesn't exist yet,height - 1)
    rect.set(xy=[x,y],facecolor=choice(colors))

    start = time.time()
    ax.draw_artist(rect)
    fig.canvas.blit(ax.bbox)
    print("draw >>>",time.time() - start)

timer = fig.canvas.new_timer(interval=1)
timer.add_callback(update)
timer.start()

plt.show()

（编辑：李大同）

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