Text.rst

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There are four kinds of text objects:

• on the 3D scene k3d.text, renders in canvas,
• on the 2D canvas k3d.text2d, renders in canvas,
• k3d.texture_text renders as texture in WebGL,
• k3d.label text in canvas, with connector to a point on the scene.

K3D-jupyter uses KaTeX for mathematical notation as a default. One can force plain html text using is_html=True option.

import k3d
import numpy as np

g = 9.81
v0 = 24

plot = k3d.plot()

for alpha_deg in [10, 30, 45, 60, 85]:
    alpha = np.radians(alpha_deg)
    t_end = 2 * v0 * np.sin(alpha) / g
    t = np.linspace(0, t_end, 100)

    # note .T at the end, k3d takes data (x1,y1,z1),(x2,y2,z2)...
    traj3d = np.stack([v0 * t * np.cos(alpha), \
                       20 * alpha + np.zeros_like(t), \
                       v0 * t * np.sin(alpha) - g * t ** 2 / 2]).T.astype(np.float32)

    plt_traj = k3d.line(traj3d)
    plt_text = k3d.text('h_{max}',
                        position=[float(np.cos(alpha) * t_end * v0 / 2),
                                  float(20 * alpha),
                                  float((v0 * np.sin(alpha)) ** 2 / (2 * g))],
                        color=0xff0000, size=1)
    plt_text2d = k3d.text2d(
        r'\text{ballistic trajectory: }\; h=v_0 t \sin \alpha - \frac{g t^2}{2}',
        position=[0.0, 0.0], color=0x0000ff, size=1)
    plt_texture_text = k3d.texture_text('START', position=[0, 0, 0],
                                        font_face='Calibri', color=255, size=5)

    if alpha_deg == 45:
        plt_label = k3d.label('Optimal angle', traj3d[-1].tolist(), mode='dynamic',
                              is_html=True, color=0xff00f0)
        plot += plt_label

    plot += plt_text
    plot += plt_text2d
    plot += plt_texture_text
    plot += plt_traj

plot.display()