"""

Drag points

===========

Example where you can drag scatter points on a line. This example also demonstrates how you can use a shared buffer

between two graphics to represent the same data using different graphics. When you update the data of one graphic the

data of the other graphic is also changed simultaneously since they use the same underlying buffer on the GPU.

"""

# test_example = false

# sphinx_gallery_pygfx_docs = 'screenshot'

import numpy as np

import fastplotlib as fpl

import pygfx

xs = np.linspace(0, 2 * np.pi, 10)

ys = np.sin(xs)

data = np.column_stack([xs, ys])

figure = fpl.Figure(size=(700, 560))

# add a line

line_graphic = figure[0, 0].add_line(data)

# add a scatter, share the line graphic buffer!

scatter_graphic = figure[0, 0].add_scatter(data=line_graphic.data, sizes=25, colors="r")

is_moving = False

vertex_index = None

@scatter_graphic.add_event_handler("pointer_down")

def start_drag(ev: pygfx.PointerEvent):

global is_moving

global vertex_index

if ev.button != 1:

return

is_moving = True

vertex_index = ev.pick_info["vertex_index"]

scatter_graphic.colors[vertex_index] = "cyan"

@figure.renderer.add_event_handler("pointer_move")

def move_point(ev):

global is_moving

global vertex_index

# if not moving, return

if not is_moving:

return

# disable controller

figure[0, 0].controller.enabled = False

# map x, y from screen space to world space

pos = figure[0, 0].map_screen_to_world(ev)

if pos is None:

# end movement

is_moving = False

scatter_graphic.colors[vertex_index] = "r" # reset color

vertex_index = None

return

# change scatter data

# since we are sharing the buffer, the line data will also change

scatter_graphic.data[vertex_index, :-1] = pos[:-1]

# re-enable controller

figure[0, 0].controller.enabled = True

@figure.renderer.add_event_handler("pointer_up")

def end_drag(ev: pygfx.PointerEvent):

global is_moving

global vertex_index

# end movement

if is_moving:

# reset color

scatter_graphic.colors[vertex_index] = "r"

is_moving = False

vertex_index = None

figure.show()

# NOTE: `if __name__ == "__main__"` is NOT how to use fastplotlib interactively

# please see our docs for using fastplotlib interactively in ipython and jupyter

if __name__ == "__main__":

print(__doc__)

fpl.loop.run()