BUG: Ensure that distinct polygon collections are shaded identically #12792
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Right now, shading ratios are computed by computing a shade in [-1, 1] for each face from the normal vector, and then normalizing across the polygon collection so that the brightest face has shade=1, and the dimmest shade=0.5. This behaves poorly with multiple polygon collections, as the normalization is internal to each. This results in two polygons with the same orientation but in different collections ending up with different shadings. Notably, this obstructs the shading of `ax.voxels()`. This approach instead scales `[-1, 1]` to `[0.4, 1]`, ignoring the local brightness minima and maxima within a collection. Some more noticeable effects of this change: * Highlights will be darker, unless they were already directly facing the light source * Contrast between extreme highlights and shadows will be slightly greater (from 1:0.5 to 1:0.4)
eric-wieser
commented
Nov 12, 2018
lib/mpl_toolkits/mplot3d/axes3d.py
Outdated
| # convert dot product to allowed shading fractions | ||
| in_norm = Normalize(-1, 1) | ||
| out_norm = Normalize(0.3, 1).inverse | ||
| norm = lambda x: out_norm(in_norm(x)) |
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0.3 was chosen to roughly give the same shading in the test-cases as before
dstansby
reviewed
Nov 14, 2018
lib/mpl_toolkits/mplot3d/axes3d.py
Outdated
| # convert dot product to allowed shading fractions | ||
| in_norm = Normalize(-1, 1) | ||
| out_norm = Normalize(0.3, 1).inverse | ||
| norm = lambda x: out_norm(in_norm(x)) |
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PEP 8 doesn't like assigning a variable to a lambda. I'm kind of indifferent but I guess it would be possible to do
def norm(x):
return out_norm(in_norm(x))There was a problem hiding this comment.
Has the extra requirement that it needs blank lines around it, which IMO makes the grouping less clear.
I guess I'll just drop the lambda, and substitute out_norm(in_norm(x)) at the call site.
|
@dstansby: PEP8 issues fixed |
anntzer
approved these changes
Dec 19, 2018
timhoffm
approved these changes
Jan 6, 2019
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Right now, shading ratios are computed by computing a shade in [-1, 1] for each face from the normal vector, and then normalizing across the polygon collection so that the brightest face has shade=1, and the dimmest shade=0.5.
This behaves poorly with multiple polygon collections, as the normalization is internal to each.
This results in two polygons with the same orientation but in different collections ending up with different shadings.
Notably, this obstructs the shading of
ax.voxels().This approach instead scales
[-1, 1]to[0.4, 1], ignoring the local brightness minima and maxima within a collection.Some more noticeable effects of this change:
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