Easily control aspect ratio

Includes being able to set aspect (e.g. if you want 1:1 aspect) and also have resize and zoom tools, etc. respect the existing aspect ratio.

[bryevdv]

@StevenCHowell FYI I have scheduled this for 0.12.7 I think all the necessary groundwork around layout is finally in place

[bryevdv]

Hi @cwhy I agree this is a very important issue, but importance is unfortunately not the only issue to consider. There is also the unavoidable matter of limited (human) resources, as well as the entire context of other competing (important) priorities, as well as any blockers that affect the order of work. In this case this feature has long been blocked by the need to re-vamp the low level layout system entirely first. To do otherwise would be to commit resources to “bolt on” a quick fix that would only get thrown away. With a very limited amount of time/work between the current team, that is just not justifiable.

However, the large layout work has been completed (or largely completed), so this implementation feature can finally begin to be discussed in detail. Unfortunately we are also passed the point where we can “experiment” with APIs. Since this feature will require new APIs we have to be certain that its the right one, so there is a higher planning, testing, documentation burned at this stage of the project. Would you care to start the discussion? If you can describe how you might like to be able to “spell” this in Bokeh, that would be helpful.