Allow clamping select mode to horizontal or vertical

[RedShift1]

Here's some shitty code for feature request #2495. Use layout.dragclamp 'h' or 'v' to clamp the selection horizontally or vertically. There's some duplicated code now, perhaps those polygon manipulations should be moved into their own functions?

[alexcjohnson]

Thanks for the PR! You're right though, we can do a bit better - first off, lets think about the attribute name: it doesn't apply to all drags, just selection drags; clamp may be OK, though I kind of like the sound of selectdirection or selectaxis better than selectclamp... dunno, @etpinard any other thoughts?

Next, we need layout.selectclamp (or whatever we call it) to be a recognized attribute here as valType: 'enumerated' with values ['h', 'v', ''] (or perhaps ['h', 'v', 'any']?), coerced from layout into fullLayout here.

Then, as you anticipated, we should avoid duplication. Something like:

var selectDirection = fullLayout.selectclamp;
if(!selectDirection) { // or !== 'any' if we go with that
    if(dy < Math.min(dx * 0.6, MINSELECT)) selectDirection = 'h';
    else if(dx < Math.min(dy * 0.6, MINSELECT)) selectDirection = 'v';
}

if(selectDirection === 'h') {
   // existing code
}
else if(selectDirection === 'v') {
    // ...
}
else {
    // ...
}

Lastly we'll need a test that covers the new functionality, probably here by dragging a diagonal (that would normally give a box constraining both dimensions) after having relayout into each mode and verifying (assertRange(selectedData.range, ...)) that you only constrain the expected dimension.

[RedShift1]

Once you decide on a name I'll create seperate PRs for

• Adding the attribute to the layout object
• Moving the polygon calculations into separate functions
• Re-implement the logic switching between clamped/non-clamped
• Tests

[RedShift1]

Are we good with the "selectdirection" name?

[etpinard]

+1 for selectdirection: 'h' | 'v' | 'any' (the default)

[alexcjohnson]

superseded by #2506