GrassField

from acron.vegetation import GrassField

class GrassField

Bases:

Bases: TypedReferenceCount

The CPU side of instanced grass: where the blades stand, in square cells round the camera, and which cells draw at which level of detail.

Blades sit on a world-anchored jittered grid of `density` blades per square metre; each grid point keeps its blade with the probability get_density_at() gives there (the masks: exclusion, water, slope, dry ground, an optional density image, and the light under an Ecosystem’s crowns), so a blade’s existence and shape depend only on its world spot and the seed – cells are seamless and come out byte-identical whenever they are rebuilt. Blades gather in clumps (after Ghost of Tsushima’s grass, Wohllaib, GDC 2021): each belongs to the nearest of a jittered lattice of clump centres, which pulls it in a little and gives it a shared height, facing and tone.

A cell’s table is one RGBA32F texel per blade, ROW blades a row: x, y, z of its root (world), and a 24-bit integer as a float: bits 0-7 its height (0..1 of the tallest), 8-15 its facing (0..2 pi), 16-23 its clump’s tone. The table is sorted by a random rank, so drawing its first n blades thins the cell evenly (the far cells draw fewer, the shader shrinks the blades past their rank as they recede).

`update(camera)` picks the cells within the last distance, gives each a level (0, 1, 2: the vertex shader’s 7, 3 or 1 segments per blade) by its nearest distance with hysteresis and a draw count, builds the tables of cells that come into range, frees those far out of it, and reports the cells whose drawing changed.

Threads: update() releases the GIL; it reads a snapshot of the terrain taken when it starts, and the field’s other methods wait for it (a lock). Limits: cells of 1 to 1024 m, at most MAX_CELL_BLADES blades a cell, and at most MAX_RANGE_CELLS cells a side in range (the last LOD distance is cut to that); a non-finite setting or camera is rejected with an error.

Inheritance diagram

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__init__()

Grass over `terrain` in cells of `cell_size` metres (1 to 1024).

build_cell()

Builds cell (cx, cy)’s blades now (in range or not); returns its slot.

clear()

Forgets every cell (after a change to the density, the masks or the ecosystem); the next update() rebuilds what is in range and reports it. Cell slots stay valid (their generation moves on).

clear_density_image()

clear_ecosystem()

property density → float

Blades per square metre where nothing thins them (default 48).

property far_fraction → float

find_cell()

The slot of cell (cx, cy), or -1 if it was never in range.

get_build_seconds()

get_canopy_response()

get_cell_draw_count()

get_cell_generation()

Counts the builds of a cell’s table: a renderer re-uploads when it moves.

get_cell_lod()

get_cell_max()

get_cell_min()

get_cell_num_blades()

get_cell_size()

get_cell_table()

The cell’s table, four floats a blade (see the class description).

get_cell_x()

get_cell_y()

get_changed()

static get_class_type()

get_clump_pull()

get_clump_size()

get_density()

get_density_at()

The probability 0..1 that a blade stands at (x, y): the exclusion and water masks clear it, steep slopes thin it, dry ground thins it a little, the density image scales it, and so does the light under an ecosystem’s crowns.

get_draw_fraction()

The share of a cell’s blades drawn at `distance`: 1 up to the thinning start, falling linearly to the far fraction at the last distance.

get_drawn_blades()

get_far_fraction()

get_hysteresis()

get_lod_cells()

get_lod_distances()

get_num_built()

get_num_cells()

get_num_changed()

get_num_visible()

is_cell_built()

is_cell_visible()

property lod_distances → LVecBase4f

x: level 0 (7 segments) up to here, y: level 1 (3 segments) up to here, level 2 (one) beyond; z: thinning starts, w: the last blade (metres).

set_canopy_response()

set_clumping()

Clumps `clump_size` metres apart (0: none); `pull` 0..1 draws each blade that far towards its clump’s centre.

set_density()

Blades per square metre where nothing thins them (default 48).

set_density_image()

A density multiplier 0..1 (grey level) over a rectangle of the world (rows north to south, as EcoTerrain’s masks); outside it, 1.

set_ecosystem()

Thins the grass under `ecosystem`’s crowns (its kept tiles’ ground light, to the power of the canopy response). Rebuild (clear()) after simulating new tiles under cells already built.

set_far_fraction()

set_hysteresis()

set_lod_distances()

x: level 0 (7 segments) up to here, y: level 1 (3 segments) up to here, level 2 (one) beyond; z: thinning starts, w: the last blade (metres).

set_slope_limits()

Full grass up to `full_degrees` of slope, none past `none_degrees`.

update()

Chooses the cells in range of `camera` and their levels, builds the tables of the new ones and frees those far behind. Returns how many cells changed (get_changed()).

write_cell_texture()

Writes a cell’s table into `texture` (RGBA32F, ROW texels wide, nearest filtering).