添加具有约束布局的外部边距？

Question

生成图形以保存到 pdf 文件时，我想调整图形相对于页面边缘的位置，例如沿所有边添加英寸边距。据我所知，这样做的解决方案（例如，在这个问题中）要么：

1. 不使用constrained_layout模式 -plt.subplots_adjust()在创建图形之后但在fig.savefig()弄乱受约束的布局之前应用
2. 实际上不要定量地调整图形的位置——添加bbox_inches="tight"或pad=-1似乎没有做任何有意义的事情

有没有一种直接的方法来调整受限布局图形的外部边距？

例如：

fig = plt.figure(constrained_layout=True, figsize=(11, 8.5))

page_grid = gridspec.GridSpec(nrows=2, ncols=1, figure=fig)

# this doesn't appear to do anything with constrained_layout=True
page_grid.update(left=0.2, right=0.8, bottom=0.2, top=0.8)

top_row_grid = gridspec.GridSpecFromSubplotSpec(1, 3, subplot_spec=page_grid[0])
for i in range(3):
    ax = fig.add_subplot(top_row_grid[:, i], aspect="equal")

n_bottom_row_plots = 10
qc_grid = gridspec.GridSpecFromSubplotSpec(1, n_bottom_row_plots, subplot_spec=page_grid[1])
for i, metric in enumerate(range(n_bottom_row_plots)):
    ax = fig.add_subplot(qc_grid[:, i])
    plt.plot(np.arange(5), np.arange(5))

fig.suptitle("my big label", fontweight="bold", fontsize="x-large", y=0.9)

# this ruins the constrained layout
# plt.subplots_adjust(left=0.2,right=0.8, bottom=0.2, top=0.8)

fig.savefig("temp.png", facecolor="coral")

产生以下结果（我想在边缘看到更多的珊瑚！）：

Answer 1

您是否尝试过使用约束布局填充选项？

fig.set_constrained_layout_pads(w_pad=4./72., h_pad=4./72.,
            hspace=0./72., wspace=0./72.)

虽然这可能有助于间距，但受限布局将限制您可以添加到定义空间的对象数量。

''' Here is the modified code '''

import matplotlib.pyplot as plt
import matplotlib.colors as mcolors
import matplotlib.gridspec as gridspec
import numpy as np


fig = plt.figure(constrained_layout=True, figsize=(11, 8.5))
fig.set_constrained_layout_pads(w_pad=2./12., h_pad=4./12.,
            hspace=0., wspace=0.)
page_grid = gridspec.GridSpec(nrows=2, ncols=1, figure=fig)

fig.suptitle("My BIG Label", fontweight="bold", fontsize="x-large", y=0.98)


# this doesn't appear to do anything with constrained_layout=True
page_grid.update(left=0.2, right=0.8, bottom=0.2, top=0.8)

top_row_grid = gridspec.GridSpecFromSubplotSpec(1, 3, subplot_spec=page_grid[0])
for i in range(3):
    ax = fig.add_subplot(top_row_grid[:, i], aspect="equal")

n_bottom_row_plots = 10
qc_grid = gridspec.GridSpecFromSubplotSpec(1, n_bottom_row_plots, subplot_spec=page_grid[1])
for i, metric in enumerate(range(n_bottom_row_plots)):
    ax = fig.add_subplot(qc_grid[:, i])
    plt.plot(np.arange(5), np.arange(5))


# this ruins the constrained layout
# plt.subplots_adjust(left=0.2,right=0.8, bottom=0.2, top=0.8)

fig.savefig("temp.png", facecolor="coral")

Answer 2

您可以设置布局引擎在其中运行的矩形。请参阅https://matplotlib.org/stable/api/layout_engine_api.htmlrect中每个引擎的参数。

不幸的是，它不是 API 的一个非常友好的部分，特别是因为TightLayoutEngine和ConstrainedLayoutEngine具有不同的语义rect：TightLayoutEngine使用rect = (left, bottom, right, top)和ConstrainedLayoutEngine使用rect = (left, bottom, width, height)。

def set_margins(fig, margins):
    """Set figure margins as [left, right, top, bottom] in inches
    from the edges of the figure."""
    left,right,top,bottom = margins
    width, height = fig.get_size_inches()
    #convert to figure coordinates:
    left, right = left/width, 1-right/width
    bottom, top = bottom/height, 1-top/height
    #get the layout engine and convert to its desired format
    engine = fig.get_layout_engine()
    if isinstance(engine, matplotlib.layout_engine.TightLayoutEngine):
        rect = (left, bottom, right, top)
    elif isinstance(engine, matplotlib.layout_engine.ConstrainedLayoutEngine):
        rect = (left, bottom, right-left, top-bottom)
    else:
        raise RuntimeError('Cannot adjust margins of unsupported layout engine')
    #set and recompute the layout
    engine.set(rect=rect)
    engine.execute(fig)

以你的例子：

fig = plt.figure(constrained_layout=True, figsize=(11, 8.5))

page_grid = gridspec.GridSpec(nrows=2, ncols=1, figure=fig)

#your margins were [0.2, 0.8, 0.2, 0.8] in figure coordinates
#which are 0.2*11 and 0.2*8.5 in inches from the edge
set_margins(fig,[0.2*11, 0.2*11, 0.2*8.5, 0.2*8.5])

top_row_grid = gridspec.GridSpecFromSubplotSpec(1, 3, subplot_spec=page_grid[0])
for i in range(3):
    ax = fig.add_subplot(top_row_grid[:, i], aspect="equal")

n_bottom_row_plots = 10
qc_grid = gridspec.GridSpecFromSubplotSpec(1, n_bottom_row_plots, subplot_spec=page_grid[1])
for i, metric in enumerate(range(n_bottom_row_plots)):
    ax = fig.add_subplot(qc_grid[:, i])
    plt.plot(np.arange(5), np.arange(5))

fig.suptitle("my big label", fontweight="bold", fontsize="x-large", y=0.9)

fig.savefig("temp.png", facecolor="coral")

注意：fig.suptitle文本显然不是由布局引擎处理的，因此它不会移动。