How to move one bezier anchor point while keeping the direction locked?
In below image I'd like to move the position of the green anchor point along the green dotted line (I freehanded in there, image it's a straight extension of the anchor point handle's line). I'd like to do so while keeping the cyan anchor point in place as well as the direction of the green line locked. Note that this is not a snapping angle (90, 45, etc) nor do I have any lines I could snap to.
Is this possible somehow?
The only way I can think of is to draw a line the direction of the green line and snap to it, but this seems very backward.
After some time playing around with this I noticed there is one much more simpler way.
With a bezier curve point selected with the
Direct selection tool (a), using the
Pen (p) tool and pressing
alt one can move the curve handles individually. With
alt pressed start moving one handle, and then holding
shift will restrain the angle of movement along the original handle direction.
This seems a lot more intuitive than the scaling method to me, because with scaling I think of objects, not points and handles. It's also more responsive to be moving the actual handle, whereas the scaling you press anywhere around the scaling center in "empty artboard".
You can use the scale tool with the tangent. Once the tangent is selected with the direct selection tool (a) click on the vertex tangent to move scale pivot to vertex. By holding Shift you can now constrain the scaling to be equal in both direction, which achieves what you want. You can also scale both tangents in unison this way.
Screencast 1: Moving tangent along existing direction by scaling uniformly.
Making a support line is also not as stupid as it sounds. But there is also a third alternative and that is to rotate the document grid temporarily to the tangent angle.