There seems to be a bug in the GGUI interface of Taichi

[lin070529]

In this official example code, the expectation for scene.lines(points_pos, color = (0.28, 0.68, 0.99), width = 5.0, vertex_count = N - 4, vertex_offset = 2) is that it will only draw 6 vertices, which translates to 3 line segments. However, when I run it, I find that it always starts drawing from the third point, resulting in 8 vertices, or 4 line segments. Additionally, in case1, the code mentioned that vertex_count will be changed to N - 2 when drawing. The expectation for scene.lines(points_pos, color = (0.28, 0.68, 0.99), width = 5.0, vertex_count = N - 1, vertex_offset = 0) is that it will only draw 8 vertices, which translates to 4 line segments. However, when I run it, I still find that it draws all the vertices, which translates to 5 line segments

import taichi as ti

ti.init(arch=ti.cuda)

N = 10

particles_pos = ti.Vector.field(3, dtype=ti.f32, shape = N)
points_pos = ti.Vector.field(3, dtype=ti.f32, shape = N)
points_indices = ti.Vector.field(1, dtype=ti.i32, shape = N)

@ti.kernel
def init_points_pos(points : ti.template()):
for i in range(points.shape[0]):
points[i] = [i for j in range(3)]
# points[i] = [ti.sin(i * 1.0), i * 0.2, ti.cos(i * 1.0)]

@ti.kernel
def init_points_indices(points_indices : ti.template()):
for i in range(N):
points_indices[i][0] = i // 2 + i % 2

init_points_pos(particles_pos)
init_points_pos(points_pos)
init_points_indices(points_indices)

window = ti.ui.Window("Test for Drawing 3d-lines", (768, 768))
canvas = window.get_canvas()
scene = ti.ui.Scene()
camera = ti.ui.Camera()
camera.position(5, 2, 2)

while window.running:
camera.track_user_inputs(window, movement_speed=0.03, hold_key=ti.ui.RMB)
scene.set_camera(camera)
scene.ambient_light((0.8, 0.8, 0.8))
scene.point_light(pos=(0.5, 1.5, 1.5), color=(1, 1, 1))

scene.particles(particles_pos, color = (0.68, 0.26, 0.19), radius = 0.1)
# Here you will get visible part from the 3rd point with (N - 4) points.
scene.lines(points_pos, color = (0.28, 0.68, 0.99), width = 5.0, vertex_count = N - 4, vertex_offset = 2)
# Using indices to indicate which vertex to use
# scene.lines(points_pos, color = (0.28, 0.68, 0.99), width = 5.0, indices = points_indices)
# Case 1, vertex_count will be changed to N - 2 when drawing.
# scene.lines(points_pos, color = (0.28, 0.68, 0.99), width = 5.0, vertex_count = N - 1, vertex_offset = 0)
# Case 2, vertex_count will be changed to N - 2 when drawing.
# scene.lines(points_pos, color = (0.28, 0.68, 0.99), width = 5.0, vertex_count = N, vertex_offset = 2)
canvas.scene(scene)
window.show()