How to access arrow positions/directions of streamplot object?

[chakravala]

How can the arrow positions and directions be accessed of a streamplot plot object?

Specifically, I'd like to update the directions of the arrows and also need the positions of the arrows too.

[chakravala]

without understanding how these plot objects work it seems difficult to access the streamplot arrow positions/directions, but somebody out there knows how to answer this with a quick solution.

[ffreyer]

The positions and directions are rather internal to plot. If you want to modify them you'll have to fight quite a bit. The arrows are drawn by p = sp.plots[2] (with sp being the streamplot), which has the positions as p.args[1]. You can get and technically also update those. But they'll also be updated by the plot if any of the arguments get updated or gridsize, stepsize, maxsteps, density or color updates:

Makie.jl/src/basic_recipes/streamplot.jl

Line 168 in 2e0aabe

data = lift(p, p.f, p.limits, p.gridsize, p.stepsize, p.maxsteps, p.density, p.color) do f, limits, resolution, stepsize, maxsteps, density, color_func

You can get the rotation from p.rotation. In 3D they are Vec3fs that set the direction of the mesh, updated by the same inputs as positions. In 2D they are rotation angles which update on scene.camera.projectionview and scene.viewport on top of the above, i.e. also when you change the view in any way.
In the end, you could do something like this

sp = streamplot!(...)
onany(sp.f, sp.limits, sp.gridsize, sp.stepsize, sp.maxsteps, sp.density, sp.color, a.scene.camera.projectionview, a.scene.viewport) do _1, _2, _3, _4, _5, _6, _7, _8, _9
    pos = sp.plots[2].args[1][]
    rot = sp.plots[2].rotation[]
    ...
    sp.plots[2].args[1][] = new_pos
    sp.plots[2].rotation[] = new_rot
end

to overwrite whatever a (2D) streamplot does whenever it updates.

[chakravala]

Excellent, thank you. Also, not sure what you mean by "changing the view in any way" as I did not need the "onany ... do" thingy when I move the 3D plot view with the mouse.

[ffreyer]

Yea the view thing only applies if the plot limits are 2D (or equivalently if sp.plots[2] isa Scatter). Otherwise (sp.plots[2] isa MeshScatter) it won't reset rotations when you change the view. The other things in the onany (other than projectionview and viewport) should still matter though. I.e. changing sp.color should overwrite your overwrites without it.