带换行的文本框

Question

有没有办法通过Matplotlib在一个框里显示文本，并且能够自动换行？我用pyplot.text()的时候，只能打印出超出窗口边界的多行文本，这让人很烦。因为行的大小事先是无法知道的……如果有任何想法，我会非常感激！

Answer 1

在创建文本框时，如果设置 wrap = True，就像下面的例子那样，这样可能会达到你想要的效果。

plt.text(5, 5, t, ha='right', rotation=-15, wrap=True)

Answer 2

大约五年过去了，但似乎还没有一个很好的方法来解决这个问题。这是我版本的一个被接受的解决方案。我的目标是让每个文本实例都能选择性地应用像素完美的换行。我还创建了一个简单的 textBox() 函数，可以把任何坐标轴转换成一个带有自定义边距和对齐方式的文本框。

我没有假设特定的字体比例或平均宽度，而是逐个单词地绘制字符串，并在达到一定阈值后插入换行。这种方法比起其他近似方法来说慢得多，但对于少于200个单词的字符串来说，感觉还是挺流畅的。

# Text Wrapping
# Defines wrapText which will attach an event to a given mpl.text object,
# wrapping it within the parent axes object.  Also defines a the convenience
# function textBox() which effectively converts an axes to a text box.
def wrapText(text, margin=4):
    """ Attaches an on-draw event to a given mpl.text object which will
        automatically wrap its string wthin the parent axes object.

        The margin argument controls the gap between the text and axes frame
        in points.
    """
    ax = text.get_axes()
    margin = margin / 72 * ax.figure.get_dpi()

    def _wrap(event):
        """Wraps text within its parent axes."""
        def _width(s):
            """Gets the length of a string in pixels."""
            text.set_text(s)
            return text.get_window_extent().width

        # Find available space
        clip = ax.get_window_extent()
        x0, y0 = text.get_transform().transform(text.get_position())
        if text.get_horizontalalignment() == 'left':
            width = clip.x1 - x0 - margin
        elif text.get_horizontalalignment() == 'right':
            width = x0 - clip.x0 - margin
        else:
            width = (min(clip.x1 - x0, x0 - clip.x0) - margin) * 2

        # Wrap the text string
        words = [''] + _splitText(text.get_text())[::-1]
        wrapped = []

        line = words.pop()
        while words:
            line = line if line else words.pop()
            lastLine = line

            while _width(line) <= width:
                if words:
                    lastLine = line
                    line += words.pop()
                    # Add in any whitespace since it will not affect redraw width
                    while words and (words[-1].strip() == ''):
                        line += words.pop()
                else:
                    lastLine = line
                    break

            wrapped.append(lastLine)
            line = line[len(lastLine):]
            if not words and line:
                wrapped.append(line)

        text.set_text('\n'.join(wrapped))

        # Draw wrapped string after disabling events to prevent recursion
        handles = ax.figure.canvas.callbacks.callbacks[event.name]
        ax.figure.canvas.callbacks.callbacks[event.name] = {}
        ax.figure.canvas.draw()
        ax.figure.canvas.callbacks.callbacks[event.name] = handles

    ax.figure.canvas.mpl_connect('draw_event', _wrap)

def _splitText(text):
    """ Splits a string into its underlying chucks for wordwrapping.  This
        mostly relies on the textwrap library but has some additional logic to
        avoid splitting latex/mathtext segments.
    """
    import textwrap
    import re
    math_re = re.compile(r'(?<!\\)\$')
    textWrapper = textwrap.TextWrapper()

    if len(math_re.findall(text)) <= 1:
        return textWrapper._split(text)
    else:
        chunks = []
        for n, segment in enumerate(math_re.split(text)):
            if segment and (n % 2):
                # Mathtext
                chunks.append('${}$'.format(segment))
            else:
                chunks += textWrapper._split(segment)
        return chunks

def textBox(text, axes, ha='left', fontsize=12, margin=None, frame=True, **kwargs):
    """ Converts an axes to a text box by removing its ticks and creating a
        wrapped annotation.
    """
    if margin is None:
        margin = 6 if frame else 0
    axes.set_xticks([])
    axes.set_yticks([])
    axes.set_frame_on(frame)

    an = axes.annotate(text, fontsize=fontsize, xy=({'left':0, 'right':1, 'center':0.5}[ha], 1), ha=ha, va='top',
                       xytext=(margin, -margin), xycoords='axes fraction', textcoords='offset points', **kwargs)
    wrapText(an, margin=margin)
    return an

使用方法：

ax = plot.plt.figure(figsize=(6, 6)).add_subplot(111)
an = ax.annotate(t, fontsize=12, xy=(0.5, 1), ha='center', va='top', xytext=(0, -6),
                 xycoords='axes fraction', textcoords='offset points')
wrapText(an)

我放弃了一些对我来说不太重要的功能。调整大小会失败，因为每次调用 _wrap() 时，都会在字符串中插入额外的换行符，但没有办法去掉它们。这个问题可以通过在 _wrap 函数中去掉所有的 \n 字符，或者把原始字符串存储在某个地方，在换行之间“重置”文本实例来解决。

Answer 3

这个回答的内容已经合并到mpl的主版本中，具体可以查看这个链接，并将在下一个功能更新中发布。

---

哇……这个问题真棘手……（而且暴露了matplotlib在文本渲染方面的很多局限性……）

我觉得这应该是matplotlib自带的功能，但实际上并没有。关于这个问题，邮件列表上有过一些讨论，但我找不到自动换行的解决方案。

首先，在matplotlib中，绘制文本之前无法确定文本字符串的像素大小。这并不是太大的问题，因为我们可以先绘制它，获取大小，然后再重新绘制换行后的文本。（虽然这样做比较耗费资源，但也不是特别糟糕）

接下来的问题是，字符的像素宽度并不是固定的，所以将文本字符串换行到指定字符数时，渲染出来的宽度可能并不准确。不过，这也不是个大问题。

更重要的是，我们不能只做一次……否则，文本在第一次绘制时（比如在屏幕上）会正确换行，但如果再次绘制（比如当图形被调整大小或以不同的DPI保存为图片时），就不会了。这也不是个大问题，因为我们可以将一个回调函数连接到matplotlib的绘制事件。

总之，这个解决方案并不完美，但在大多数情况下应该能用。我没有考虑到用tex渲染的字符串、任何拉伸的字体，或者比例不寻常的字体。不过，现在它应该能正确处理旋转的文本。

此外，它应该会尝试自动换行任何在多个子图中的文本对象，只要你将on_draw回调连接到的图形中……虽然在很多情况下效果并不完美，但表现还不错。

import matplotlib.pyplot as plt

def main():
    fig = plt.figure()
    plt.axis([0, 10, 0, 10])

    t = "This is a really long string that I'd rather have wrapped so that it"\
    " doesn't go outside of the figure, but if it's long enough it will go"\
    " off the top or bottom!"
    plt.text(4, 1, t, ha='left', rotation=15)
    plt.text(5, 3.5, t, ha='right', rotation=-15)
    plt.text(5, 10, t, fontsize=18, ha='center', va='top')
    plt.text(3, 0, t, family='serif', style='italic', ha='right')
    plt.title("This is a really long title that I want to have wrapped so it"\
             " does not go outside the figure boundaries", ha='center')

    # Now make the text auto-wrap...
    fig.canvas.mpl_connect('draw_event', on_draw)
    plt.show()

def on_draw(event):
    """Auto-wraps all text objects in a figure at draw-time"""
    import matplotlib as mpl
    fig = event.canvas.figure

    # Cycle through all artists in all the axes in the figure
    for ax in fig.axes:
        for artist in ax.get_children():
            # If it's a text artist, wrap it...
            if isinstance(artist, mpl.text.Text):
                autowrap_text(artist, event.renderer)

    # Temporarily disconnect any callbacks to the draw event...
    # (To avoid recursion)
    func_handles = fig.canvas.callbacks.callbacks[event.name]
    fig.canvas.callbacks.callbacks[event.name] = {}
    # Re-draw the figure..
    fig.canvas.draw()
    # Reset the draw event callbacks
    fig.canvas.callbacks.callbacks[event.name] = func_handles

def autowrap_text(textobj, renderer):
    """Wraps the given matplotlib text object so that it exceed the boundaries
    of the axis it is plotted in."""
    import textwrap
    # Get the starting position of the text in pixels...
    x0, y0 = textobj.get_transform().transform(textobj.get_position())
    # Get the extents of the current axis in pixels...
    clip = textobj.get_axes().get_window_extent()
    # Set the text to rotate about the left edge (doesn't make sense otherwise)
    textobj.set_rotation_mode('anchor')

    # Get the amount of space in the direction of rotation to the left and 
    # right of x0, y0 (left and right are relative to the rotation, as well)
    rotation = textobj.get_rotation()
    right_space = min_dist_inside((x0, y0), rotation, clip)
    left_space = min_dist_inside((x0, y0), rotation - 180, clip)

    # Use either the left or right distance depending on the horiz alignment.
    alignment = textobj.get_horizontalalignment()
    if alignment is 'left':
        new_width = right_space 
    elif alignment is 'right':
        new_width = left_space
    else:
        new_width = 2 * min(left_space, right_space)

    # Estimate the width of the new size in characters...
    aspect_ratio = 0.5 # This varies with the font!! 
    fontsize = textobj.get_size()
    pixels_per_char = aspect_ratio * renderer.points_to_pixels(fontsize)

    # If wrap_width is < 1, just make it 1 character
    wrap_width = max(1, new_width // pixels_per_char)
    try:
        wrapped_text = textwrap.fill(textobj.get_text(), wrap_width)
    except TypeError:
        # This appears to be a single word
        wrapped_text = textobj.get_text()
    textobj.set_text(wrapped_text)

def min_dist_inside(point, rotation, box):
    """Gets the space in a given direction from "point" to the boundaries of
    "box" (where box is an object with x0, y0, x1, & y1 attributes, point is a
    tuple of x,y, and rotation is the angle in degrees)"""
    from math import sin, cos, radians
    x0, y0 = point
    rotation = radians(rotation)
    distances = []
    threshold = 0.0001 
    if cos(rotation) > threshold: 
        # Intersects the right axis
        distances.append((box.x1 - x0) / cos(rotation))
    if cos(rotation) < -threshold: 
        # Intersects the left axis
        distances.append((box.x0 - x0) / cos(rotation))
    if sin(rotation) > threshold: 
        # Intersects the top axis
        distances.append((box.y1 - y0) / sin(rotation))
    if sin(rotation) < -threshold: 
        # Intersects the bottom axis
        distances.append((box.y0 - y0) / sin(rotation))
    return min(distances)

if __name__ == '__main__':
    main()