我想創(chuàng)建一個包含箭頭的matplotlib圖，其頭部的形狀與數(shù)據(jù)坐標(biāo)無關(guān)。這類似于FancyArrowPatch，但是當(dāng)箭頭長度小于頭部長度時，會收縮以適應(yīng)箭頭的長度。目前，我通過將寬度轉(zhuǎn)換為顯示坐標(biāo)、計算顯示坐標(biāo)中的頭部長度并將其轉(zhuǎn)換回數(shù)據(jù)坐標(biāo)來設(shè)置箭頭的長度來解決這個問題。只要軸的尺寸不發(fā)生變化，這種方法就可以很好地工作，這可能是由于set_xlim()，set_ylim()或tight_layout()例如。我想通過在繪圖尺寸發(fā)生變化時重新繪制箭頭來涵蓋這些情況。目前我通過注冊一個函數(shù)on_draw(event)來處理這個axes.get_figure().canvas.mpl_connect("resize_event", on_draw)但這僅適用于交互式后端。我還需要一個解決方案，將繪圖保存為圖像文件。還有其他地方可以注冊我的回調(diào)函數(shù)嗎？
2 回答
Helenr
TA貢獻1780條經(jīng)驗 獲得超4個贊
我找到了該問題的解決方案，但是，它不是很優(yōu)雅。我發(fā)現(xiàn)，在非交互式后端調(diào)用的唯一回調(diào)函數(shù)是子類的draw_path()方法AbstractPathEffect。
我創(chuàng)建了一個AbstractPathEffect子類，在其draw_path()方法中更新箭頭的頂點。
我仍然愿意為我的問題提供其他可能更直接的解決方案。
import numpy as np
from numpy.linalg import norm
from matplotlib.patches import FancyArrow
from matplotlib.patheffects import AbstractPathEffect
class AdaptiveFancyArrow(FancyArrow):
"""
A `FancyArrow` with fixed head shape.
The length of the head is proportional to the width the head
in display coordinates.
If the head length is longer than the length of the entire
arrow, the head length is limited to the arrow length.
"""
def __init__(self, x, y, dx, dy,
tail_width, head_width, head_ratio, draw_head=True,
shape="full", **kwargs):
if not draw_head:
head_width = tail_width
super().__init__(
x, y, dx, dy,
width=tail_width, head_width=head_width,
overhang=0, shape=shape,
length_includes_head=True, **kwargs
)
self.set_path_effects(
[_ArrowHeadCorrect(self, head_ratio, draw_head)]
)
class _ArrowHeadCorrect(AbstractPathEffect):
"""
Updates the arrow head length every time the arrow is rendered
"""
def __init__(self, arrow, head_ratio, draw_head):
self._arrow = arrow
self._head_ratio = head_ratio
self._draw_head = draw_head
def draw_path(self, renderer, gc, tpath, affine, rgbFace=None):
# Indices to certain vertices in the arrow
TIP = 0
HEAD_OUTER_1 = 1
HEAD_INNER_1 = 2
TAIL_1 = 3
TAIL_2 = 4
HEAD_INNER_2 = 5
HEAD_OUTER_2 = 6
transform = self._arrow.axes.transData
vert = tpath.vertices
# Transform data coordiantes to display coordinates
vert = transform.transform(vert)
# The direction vector alnog the arrow
arrow_vec = vert[TIP] - (vert[TAIL_1] + vert[TAIL_2]) / 2
tail_width = norm(vert[TAIL_2] - vert[TAIL_1])
# Calculate head length from head width
head_width = norm(vert[HEAD_OUTER_2] - vert[HEAD_OUTER_1])
head_length = head_width * self._head_ratio
if head_length > norm(arrow_vec):
# If the head would be longer than the entire arrow,
# only draw the arrow head with reduced length
head_length = norm(arrow_vec)
# The new head start vector; is on the arrow vector
if self._draw_head:
head_start = \
vert[TIP] - head_length * arrow_vec/norm(arrow_vec)
else:
head_start = vert[TIP]
# vector that is orthogonal to the arrow vector
arrow_vec_ortho = vert[TAIL_2] - vert[TAIL_1]
# Make unit vector
arrow_vec_ortho = arrow_vec_ortho / norm(arrow_vec_ortho)
# Adjust vertices of the arrow head
vert[HEAD_OUTER_1] = head_start - arrow_vec_ortho * head_width/2
vert[HEAD_OUTER_2] = head_start + arrow_vec_ortho * head_width/2
vert[HEAD_INNER_1] = head_start - arrow_vec_ortho * tail_width/2
vert[HEAD_INNER_2] = head_start + arrow_vec_ortho * tail_width/2
# Transform back to data coordinates
# and modify path with manipulated vertices
tpath.vertices = transform.inverted().transform(vert)
renderer.draw_path(gc, tpath, affine, rgbFace)
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