Text waterfall

An example showing a waterfall of text. On the left it shows the contents of the glyph atlas. One goal of this example is to strain the text rendering to its limits.

from wgpu.gui.auto import WgpuCanvas, run
import pygfx as gfx
import numpy as np


renderer = gfx.renderers.WgpuRenderer(WgpuCanvas(size=(800, 400)))
scene = gfx.Scene()
glyph_atlas = gfx.utils.text.glyph_atlas
glyph_atlas.clear_free_regions = True  # So we can see regions being freed

# Add background
background = gfx.Background(None, gfx.BackgroundMaterial("#dde", "#fff"))
scene.add(background)

# Add an image that shows the glyph atlas
atlas_viewer = gfx.Mesh(
    gfx.plane_geometry(100, 100),
    gfx.MeshBasicMaterial(color="red"),
)
scene.add(atlas_viewer)
atlas_viewer.local.x = -50

camera = gfx.OrthographicCamera(200, 100)

# Create a bunch of reusable text objects


def character_generator():
    pieces = gfx.font_manager.select_font(" ", gfx.font_manager.default_font_props)
    font = pieces[0][1]
    while True:
        for c in font.codepoints:
            yield chr(c)


chargen = character_generator()

live_objects = set()
waiting_objects = set()

text_material = gfx.TextMaterial(color="#06E")

for i in range(100):
    obj = gfx.Text(
        gfx.TextGeometry(" ", font_size=18, screen_space=True),
        text_material,
    )
    scene.add(obj)
    waiting_objects.add(obj)
    obj.local.y = -999


# The animate function makes the text objects fall down, and update the objects
# with a new character once they start their fall again.
# Until we have real garbage collection for glyphs, we fake it here.


def animate():
    garbage_collect = True

    # Let them fall
    for obj in list(live_objects):
        obj.local.y -= obj.fall_speed
        if obj.local.y < -60:
            live_objects.discard(obj)
            waiting_objects.add(obj)
            if garbage_collect:
                all_indices = set()
                for x in live_objects:
                    all_indices.update(int(index) for index in x.geometry.indices.data)
                for index in obj.geometry.indices.data:
                    index = int(index)
                    if index not in all_indices:
                        glyph_atlas.free_region(index)

    # Drop new objects
    if waiting_objects:
        obj = waiting_objects.pop()
        live_objects.add(obj)
        obj.local.y = 50
        obj.local.x = np.random.uniform(0, 100)
        obj.geometry.set_text(next(chargen))
        obj.fall_speed = np.random.uniform(1, 4)

    # Update the image
    if atlas_viewer.material.map is not glyph_atlas.texture:
        atlas_viewer.material.map = glyph_atlas.texture

    # Render
    renderer.render(scene, camera)
    renderer.request_draw()


if __name__ == "__main__":
    renderer.request_draw(animate)
    run()