handling colors and other modifiable attributes

[kushalkolar]

The way colors are handled by Graphic is kinda of wonky now, I'm thinking of making a base class GraphicAttribute which is indexable, this would allow intuitive fine grained color control. It would probably also fix the current wonkyness of ScatterGraphic.

example:

plot = Plot()

line_graphic = plot.line(data=<sine_wave>)

line_graphic.colors[50:100] = "red"
line_graphic.colors[100:] = (0, 1, 0, 1)
line_graphic.colors = "w"
...

This would basically call pygfx geometry/material colors.data and the update_range() for only the indices modified

@EricThomson @clewis7 thoughts?

@clewis7 this will get rid of all the current update_<graphic_attr> methods, but we can change that later. For interactivity we can just allow anything that is a GraphicAttribute instance to be a modifiable feature.

[EricThomson]

This seems great I really like it! Would make certain things really intuitive and simple.

[kushalkolar]

Could also add sizes, at least for scatter, might also be possible for line

[kushalkolar]

@clewis7 once #61 is merged we need to think of how to trigger events when a GraphicAttribute changes its data, will have to work for Graphic and GraphicCollection objects.

[kushalkolar]

for now thing left to do is sizes

[kushalkolar]

mostly implemented in #78 and #88, this issue superseeded by #85