Allow custom fill endpoints in a filled plot

[kcrisman]

In this ask.sagemath question, the issue is raised whether

sage: f = x*(x-1)*(x-2)+1
sage: p = plot(f, 0.5, 1.5, fill=True) + plot(f, 0, 2)

should be doable in a single command, such as with a fillxmin/fillxmax keyword (or some better name).

CC: @sagetrac-dsm @vbraun

Component: graphics

Author: Sergey Bykov

Branch/Commit: u/captaintrunky/allow_custom_fill_endpoints_in_a_filled_plot @ 2f0fdcb

Issue created by migration from https://trac.sagemath.org/ticket/14599

[sagetrac-captaintrunky]

Branch: u/captaintrunky/allow_custom_fill_endpoints_in_a_filled_plot

[sagetrac-captaintrunky]

Author: Sergey Bykov

[sagetrac-captaintrunky]

Commit: c4cbac3

[sagetrac-captaintrunky]

New commits:

c4cbac3

Added custom endpoints in a filled plot

[kcrisman]

comment:7

This is great that you are working on this! I don't see any obvious problems in the code, though I won't be able to look at it more carefully right now. My first thought, though, is what happens with parametric plots? Somehow their fill "magically" works right, and I'm wondering what the behavior might be with this keyword.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

4c8dc26

Fixed fill for parametric curves

[sagetrac-git]

Changed commit from c4cbac3 to 4c8dc26

[sagetrac-captaintrunky]

comment:9

Replying to @kcrisman:

This is great that you are working on this! I don't see any obvious problems in the code, though I won't be able to look at it more carefully right now. My first thought, though, is what happens with parametric plots? Somehow their fill "magically" works right, and I'm wondering what the behavior might be with this keyword.

Thanks for the feedback. You were right, there was some weird staff with parametric curves. It seems to work fine now, but these new custom endpoints definitely require some additional checks. However, I couldn't break it with my test suite, which contains a set of well-known curves.

[kcrisman]

comment:10

Hmm, maybe you can add some of those to the tests/examples; at any rate, currently your branch has only one non-example, not examples of how to use this. Or, if you have a pretty extensive suite, there are a couple testing-only files out there that could be added to - we love tests!

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

2f0fdcb

Adds some examples of custom fill endpoints

[sagetrac-git]

Changed commit from 4c8dc26 to 2f0fdcb

[kcrisman]

comment:12

Look at the following interesting behavior.

sage: plot([x^3,x^2,x], xmin=0, xmax=4, fill={0:[1], 1:1, 2:1-x}, fillxmin=1, fillxmax=2)

It's definitely obeying the fillxmax but not in the way one might expect.

Similarly, I'm not sure that

sage: plot((cos(x),sin(x)), xmin=0, xmax=2*pi, parametric=True, fill=True, fillxmin=0.5)

is behaving as expected.

And I'm completely flummoxed as to why

sage: plot((cos(x),sin(x)), xmin=0, xmax=2*pi, parametric=True, fill=True, fillxmin=1)
<boom>
KeyError: 'text/plain'

due to the new display hook stuff!

One possible workaround would be to disallow the custom fill (for now) in parametric plots (i.e. raise an error) and make that a new ticket. I do think that the first 'bad' example should be dealt with, though.

[vbraun]

comment:13

the problem is probably that the plot object is invalid (it can't actually show a plot). Because there is insufficient validation this only causes issues later when you actually try to plot it.

[kcrisman]

comment:14

Hmm, that makes sense. I have to say that the error is a little cryptic.

[DaveWitteMorris]

comment:15

Removing the "beginner" tag from old tickets. Some could be returned to beginner-friendly status by adding a comment about what needs to be done. Some others might be easy for an experienced developer to finish.