Envelopes

[srush]

Notes on Envelopes from reading Pearl.

• Replace cached bounding box on Diagrams with Envelope class.
• Primitives can still return bounding boxes, ie for rect, spacer, etc. Diagram will wrap these in a function that returns distance to boundaries from origin.
• For paths of segments, we compute convex hull? Envelope computes distance to nearest half space.
• For circle it returns L2 * radius of vector?
• For arcs it is l2 is pointing in. -l2 if pointing out, and otherwise ...? (Distance to tangent at last angle?)
• For text, the envelope always returns 0
• Transformables are implemented for envelopes like Traces.
• For atop, simply max the resulting envelope (since origin is shared).
• For concat, we should special case it for efficiency. Take the max of all diagrams in one function to avoid n-calls.
• Envelope class might have some of the same properties as bounding box. Left, right, width, height. Although perhaps this is misleading if it is rotated.

Questions:

• Does additive pad make sense any longer? Diagrams uses multiplicative.
• Should we add directionally oriented atop? Is that useful?
• How do we envelope paths with arcs in them? Or just arcs?
• Should we allow using bounding boxes still? Might be more efficient in some cases.

[danoneata]

I'll just leave here some further pointers to the diagrams library for future reference (they both have some useful notes in the comments):

• envelopes for segments and arcs
• transformations on envelopes

[srush]

Gonna declare success here. Traces and envelopes seems strictly better and not really a speed issue at all. Neither required too much complexity.