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"""
The AxesCache class alters how an Axes instance is rendered.
While enabled, the AxesCache quickly re-renders an original view,
properly scaled and translated to reflect changes in the viewport.
The downside is that the re-rendered image is fuzzy and/or truncated.
The best way to use an AxesCache is to enable it during
window resize drags and pan/zoom mouse drags; these generate
rapid draw requests, and users might prefer high refresh
rates to pixel-perfect renders.
Unfortunately, Matplotlib on it's own doesn't provide an easy
mechanism to attach event handlers to either window resize drags
or pan/zoom drags. This code must be added separately.
"""
import numpy as np
from matplotlib.axes import Axes
from matplotlib.image import AxesImage
from matplotlib.collections import QuadMesh
class RenderCapture(object):
"""
A RemderCapture saves an image of a fully-rendered
Axes instance, and provides a method for re-rendering
a properly transformed image during panning and zooming
"""
def __init__(self, axes, renderer):
self.axes = axes
self._corners = self._get_corners(axes)
px, py, dx, dy = self._corners
im = self.extract_image(renderer)
im = im[py[0]: py[-1] + 1, px[0]: px[-1] + 1, :]
self.im = im
self._mesh = None
self._image = None
self.image
@property
def image(self):
if self._image is not None:
return self._image
px, py, dx, dy = self._corners
self._image = AxesImage(self.axes,
origin='lower',
interpolation='nearest')
self._image.set_data(self.im)
self._image.set_extent((dx[0], dx[-1], dy[0], dy[-1]))
self.axes._set_artist_props(self._image)
return self._image
@property
def mesh(self):
if self._mesh is not None:
return self._mesh
px, py, dx, dy = self._corners
x, y, c = self.axes._pcolorargs('pcolormesh', dx, dy,
self.im[:, :, 0],
allmatch=False)
ny, nx = x.shape
coords = np.column_stack((x.ravel(), y.ravel()))
collection = QuadMesh(nx - 1, ny - 1, coords,
shading='flat', antialiased=False,
edgecolors='None',
cmap='gray')
collection.set_array(c.ravel())
collection.set_clip_path(self.axes.patch)
collection.set_transform(self.axes.transData)
self._mesh = collection
return self._mesh
def draw(self, renderer, *args, **kwargs):
if self.axes.get_xscale() == 'linear' and \
self.axes.get_yscale() == 'linear':
self.image.draw(renderer, *args, **kwargs)
else:
self.mesh.draw(renderer, *args, **kwargs)
@staticmethod
def _get_corners(axes):
"""
Return the device and data coordinates
for a box slightly inset from the edge
of an axes instance
Returns 4 1D arrays:
px : Pixel X locations for each column of the box
py : Pixel Y locations for each row of the box
dx : Data X locations for each column of the box
dy : Data Y locations for each row of the box
"""
xlim = axes.get_xlim()
ylim = axes.get_ylim()
pts = np.array([[xlim[0], ylim[0]],
[xlim[1], ylim[1]]])
corners = axes.transData.transform(pts).astype(np.int)
# move in 5 pixels, to avoid grabbing the tick marks
px = np.arange(corners[0, 0] + 5, corners[1, 0] - 5)
py = np.arange(corners[0, 1] + 5, corners[1, 1] - 5)
tr = axes.transData.inverted().transform
dx = tr(np.column_stack((px, px)))[:, 0]
dy = tr(np.column_stack((py, py)))[:, 1]
return px, py, dx, dy
@staticmethod
def extract_image(renderer):
try:
buf = renderer.buffer_rgba()
except TypeError: # mpl v1.1 has different signature
buf = renderer.buffer_rgba(0, 0)
result = np.frombuffer(buf, dtype=np.uint8)
result = result.reshape((int(renderer.height),
int(renderer.width), 4)).copy()
return np.flipud(result)
class AxesCache(object):
def __init__(self, axes):
self.axes = axes
self._capture = None
self.axes.draw = self.draw
self._enabled = False
def draw(self, renderer, *args, **kwargs):
if self._capture is None or not self._enabled:
Axes.draw(self.axes, renderer, *args, **kwargs)
if hasattr(renderer, 'buffer_rgba'):
self._capture = RenderCapture(self.axes, renderer)
else:
self.axes.axesPatch.draw(renderer, *args, **kwargs)
self._capture.draw(renderer, *args, **kwargs)
self.axes.xaxis.draw(renderer, *args, **kwargs)
self.axes.yaxis.draw(renderer, *args, **kwargs)
for s in self.axes.spines.values():
s.draw(renderer, *args, **kwargs)
def clear_cache(self):
"""
Clear the cache, forcing the a full re-render
"""
self._capture = None
def disable(self):
"""
Temporarily disable cache re-renders. Render
results are still saved, for when
enable() is next called
"""
self._enabled = False
self.axes.figure.canvas.draw()
def enable(self):
"""
Enable cached-rerenders
"""
self._enabled = True
def teardown(self):
"""
Permanently disable this cache, and restore
normal Axes render behavior
"""
self.axes.draw = Axes.draw.__get__(self.axes)
if __name__ == "__main__":
import matplotlib.pyplot as plt
num = 1000000
plt.subplot(111)
plt.subplots_adjust(bottom=.5, top=.8)
plt.scatter(np.random.randn(num), np.random.randn(num),
s=np.random.randint(10, 50, num),
c=np.random.randint(0, 255, num),
alpha=.2, linewidths=0)
plt.plot([0, 1, 2, 3], [0, 1, 2, 3])
cache = AxesCache(plt.gca())
cache.enable()
plt.grid('on')
# plt.xscale('log')
plt.show()
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