matplotlib 高阶之path tutorial

Bezier example
用path来画柱状图
随便玩玩

import matplotlib.pyplot as plt

from matplotlib.path import Path

import matplotlib.patches as patches

Path 通过一个(N, 2)的包含(x, y)的点来实例比如，我们想要画一个标准的正方形：

verts = [

   (0., 0.),  # left, bottom

   (0., 1.),  # left, top

   (1., 1.),  # right, top

   (1., 0.),  # right, bottom

   (0., 0.),  # ignored

]

codes = [

    Path.MOVETO,

    Path.LINETO,

    Path.LINETO,

    Path.LINETO,

    Path.LINETO,

]

path = Path(verts, codes)

fig, ax = plt.subplots(figsize=(5, 5))

patch = patches.PathPatch(path, facecolor='orange', lw=2)

ax.add_patch(patch)

ax.set_xlim(-2, 2)

ax.set_ylim(-2, 2)

plt.show()

注意到，上面的codes包含了一些path的种类：

STOP: 标志着整个path的结束

MOVETO: 提起笔，移动到当前给定的位置 path的第一个点必须是MOVETO 表示提起笔？

LINETO: 画一条从当前位置到给定点的直线

CURVE3: 需要给定一个控制点和一个结束点画一个二次Bézier曲线，利用控制点到结束点

CURVE4: 需要给定俩个控制点和一个街书店，画一个三次Beier曲线，利用给定的控制点到结束点

Bezier example

有些path需要多个点来确定，比如上面的CURVE3要2个点CURVE4需要3个点

verts = [

   (0., 0.),   # P0

   (0.2, 1.),  # P1

   (1., 0.8),  # P2

   (0.8, 0.),  # P3

]

codes = [

    Path.MOVETO,

    Path.CURVE4, #我们看到CURVE4占了3个点

    Path.CURVE4,

    Path.CURVE4,

]

path = Path(verts, codes)

fig, ax = plt.subplots()

patch = patches.PathPatch(path, facecolor='none', lw=2)

ax.add_patch(patch)

xs, ys = zip(*verts)

ax.plot(xs, ys, 'x--', lw=2, color='black', ms=10)

ax.text(-0.05, -0.05, 'P0')

ax.text(0.15, 1.05, 'P1')

ax.text(1.05, 0.85, 'P2')

ax.text(0.85, -0.05, 'P3')

ax.set_xlim(-0.1, 1.1)

ax.set_ylim(-0.1, 1.1)

plt.show()

用path来画柱状图

matplotlib里面的很多元素，比如hist, bar等都是以path为图元的

import numpy as np

nrects = 100

data = np.random.randn(1000)

n, bins = np.histogram(data, nrects) # n每个bin的个数， bins位置

left = np.array(bins[:-1]) #矩形的左边位置

right = np.array(bins[1:]) #矩形的右边位置

bottom = np.zeros(nrects) #下

top = bottom + n #上

接下来，我们来构建柱状体，每个柱子需要5个点,一个MOVETO，三个LINETO，一个CLOSEPOLY

nverts = nrects*(1+3+1)

verts = np.zeros((nverts, 2)) #构建nevrts * 2 的数组

codes = np.ones(nverts, int) * Path.LINETO #LINETO == 2

codes[0::5] = Path.MOVETO #每隔五步是一个新的起点 MOVETO == 1

codes[4::5] = Path.CLOSEPOLY  #同样有一个终点 CLOSEPOLY == 79

verts[0::5,0] = left #下面都是设置起始位置

verts[0::5,1] = bottom

verts[1::5,0] = left

verts[1::5,1] = top

verts[2::5,0] = right

verts[2::5,1] = top

verts[3::5,0] = right

verts[3::5,1] = bottom

barpath = Path(verts, codes)

patch = patches.PathPatch(barpath, facecolor='green',

  edgecolor='yellow', alpha=0.5)

fig, ax = plt.subplots()

ax.add_patch(patch)

ax.set_xlim(left[0], right[-1])  #坐标不会自动调整，需要自己设定

ax.set_ylim(bottom.min(), top.max())

plt.show()

随便玩玩

verts = [

    (1, 0),

    (0, 1),

    (2, 2),

    (3, 3.5),

    (4, 3.2),

    (3.6, 0)

]

codes = [

    Path.MOVETO,

    Path.CURVE3,

    Path.CURVE3,

    Path.CURVE4,

    Path.CURVE4,

    Path.CURVE4

]

linepath = Path(verts, codes)

pathce = patches.PathPatch(linepath, facecolor="yellow", edgecolor="red")

fig, ax  = plt.subplots()

ax.add_patch(pathce)

ax.set_xlim(0, 5)

ax.set_ylim(0, 4)

plt.show()

verts = [

    (0, 0),

    (0, 2.7),

    (-0.8, 2),

    (0.8, 2),

    (-0.3, 2.7),

    (0.3, 2.7),

    (-0.4, 4.1),

    (0.4, 4.1),

    (-0.35, 3.4),

    (0.35, 3.4),

    (-0.3, 2.7),

    (-0.4, 4.1),

    (0.3, 2.7),

    (0.4, 4.1)

]

codes = [

    Path.MOVETO,

    Path.LINETO,

    Path.MOVETO,

    Path.LINETO,

    Path.MOVETO,

    Path.LINETO,

    Path.MOVETO,

    Path.LINETO,

    Path.MOVETO,

    Path.LINETO,

    Path.MOVETO,

    Path.LINETO,

    Path.MOVETO,

    Path.LINETO

]

zaopath = Path(verts, codes)

patch = patches.PathPatch(zaopath, edgecolor="blue")

fig, ax = plt.subplots()

ax.add_patch(patch)

ax.set_xlim(-1, 1)

ax.set_ylim(-1, 5)

plt.show()

巴特西

matplotlib 高阶之path tutorial

Bezier example

用path来画柱状图

随便玩玩

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