8000 Fix data cursor for images with additional transform by alexschlueter · Pull Request #18737 · matplotlib/matplotlib · GitHub
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Fix data cursor for images with additional transform #18737

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Jan 5, 2021
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Fix data cursor for images with additional transform #18737

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12fbe4a
Fix image data cursor when artist has additional transform
alexschlueter Oct 14, 2020
7a91945
Add test for data cursor on transformed image
alexschlueter Oct 15, 2020
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14 changes: 8 additions & 6 deletions lib/matplotlib/image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -661,7 +661,8 @@ def contains(self, mouseevent):
# collection on nonlinear transformed coordinates.
# TODO: consider returning image coordinates (shouldn't
# be too difficult given that the image is rectilinear
x, y = mouseevent.xdata, mouseevent.ydata
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Since you aren't using xdata/ydata any more, does that mean the comment about about figimage is fixed?

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I believe it should be fine to remove the self.axes is not mouseevent.inaxes check now and contains() should also work for FigureImage. However, FigureImage doesn't have a get_cursor_data() yet, so I think the only place where contains would be used for a FigureImage is for the pick events? I'm not sure about that though, maybe @anntzer can help since he wrote the original comment.

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It's likely that this fixes some of the problems I had noticed when I put in the comment, but I haven't reviewed this carefully enough to see whether all problems are indeed fixed.

trans = self.get_transform().inverted()
x, y = trans.transform([mouseevent.x, mouseevent.y])
xmin, xmax, ymin, ymax = self.get_extent()
if xmin > xmax:
xmin, xmax = xmax, xmin
Expand Down Expand Up @@ -983,13 +984,14 @@ def get_cursor_data(self, event):
if self.origin == 'upper':
ymin, ymax = ymax, ymin
arr = self.get_array()
data_extent = Bbox([[ymin, xmin], [ymax, xmax]])
array_extent = Bbox([[0, 0], arr.shape[:2]])
trans = BboxTransform(boxin=data_extent, boxout=array_extent)
point = trans.transform([event.ydata, event.xdata])
data_extent = Bbox([[xmin, ymin], [xmax, ymax]])
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I'm confused - was the previous version just a huge bug?

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Are you referring to the switched xdata and ydata coordinates in the original version? I think this was fine originally (this code was covered quite well by tests in test_cursor_data()).
The first index of the array runs along the y-axis, while the second index runs along the x-axis. This means that a flip has to happen somewhere.
Originally, the flip was in the line point = trans.transform([event.ydata, event.xdata]). However, since we now want to apply a different transform first, we have to input the points in the right order (first x, then y). The flip still has to happen though, so we instead flip arr.shape and change i, j to j, i when we get the result.

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I got it - I didn't trace it all through so was confused...

array_extent = Bbox([[0, 0], [arr.shape[1], arr.shape[0]]])
trans = self.get_transform().inverted()
trans += BboxTransform(boxin=data_extent, boxout=array_extent)
point = trans.transform([event.x, event.y])
if any(np.isnan(point)):
return None
i, j = point.astype(int)
j, i = point.astype(int)
# Clip the coordinates at array bounds
if not (0 <= i < arr.shape[0]) or not (0 <= j < arr.shape[1]):
return None
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9 changes: 9 additions & 0 deletions lib/matplotlib/tests/test_image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -324,6 +324,15 @@ def test_cursor_data():
event = MouseEvent('motion_notify_event', fig.canvas, xdisp, ydisp)
assert im.get_cursor_data(event) is None

# Now try with additional transform applied to the image artist
trans = Affine2D().scale(2).rotate(0.5)
im = ax.imshow(np.arange(100).reshape(10, 10),
transform=trans + ax.transData)
x, y = 3, 10
xdisp, ydisp = ax.transData.transform([x, y])
event = MouseEvent('motion_notify_event', fig.canvas, xdisp, ydisp)
assert im.get_cursor_data(event) == 44


@pytest.mark.parametrize(
"data, text_without_colorbar, text_with_colorbar", [
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0