Feature: to_html implemented

[wwy155]

Feature: to_html finished

1. I guess there are only two type of html can be exported as, which are

• canvas (pixels graph)
• svg (vector graph)

luckily , although they are two different type of graph , canvas is transformed just the same as svg.so thanks to @jojolebarjos , I can finish part of "to_canvas" quickly with reference to his to_svg method.

Here are some differences I've found bettween canvas and svg:

1. canvas's performance in html is much better than svg
2. canvas won't load the font automatically, so I need to write some javascript code in my html template and put a div tag in int to load the font

Fix: text overlap

2. support font family will fix the texts overlap problem in to_svg method

when I tested the to_svg method, I found there are some text overllaped together , but after I add a font family attribute , the problem is gone

some problems

3. some problems

• the font load mechanism I am using might have some compability issues, but I am pretty sure it worked well in chrome and miscrosoft edge
• there's a a lot repeat code fragment in to_svg and to_canvas methods , may need a refactoring here

[wwy155]

why can't I pass those checks ........ 😭

[amueller]

hey! Thanks for the PR. I thought I had remove the method, as I figured the SVG export would be enough.
Do you feel like having html output in addition to SVG is useful? What would be the use cases?

[amueller]

Also, I think, CI is just broken right now and it's not your fault :(