Crate aquarelle 

aquarelle — watercolor-style soft-bleed orb rendering on a tiny_skia::Pixmap.

Originally written as the cel-anime night-scene texture set for the orber abstract-mood-image generator, the engine is independent of orber and only depends on tiny-skia + palette + rand + rand_chacha. It takes a center, radius, RGB color, and a u64 seed, and draws four compositable elements onto a pixel buffer you already own.

The four elements

1. bleed — small same-color radial gradients scattered around the orb to fake a film grain / paper-bleed feel.
2. bloom — a near-white core inside the inner ~30 % of the radius so the orb reads as a light source rather than a flat dot.
3. offset — the gradient center is decoupled from the geometric center by up to 25 % of the radius. A perfectly concentric light source looks artificial; a slightly off-center one feels natural. The direction is seed-derived so calls are deterministic.
4. halo — saturation of the outer falloff is boosted so the bleed reads as a film halation instead of a flat alpha fade.

Each is tunable in 0.0..=1.0 and they compose with source-over.

Renderer-agnostic on purpose

aquarelle does not know what background is on the pixmap, what the rest of your scene looks like, or how you intend to encode the result. It just composites four watercolor layers onto the buffer you hand it. The caller decides the background fill, layout, and output format (PNG / WebP / SVG / animation frames / WebCodecs).

Example

use aquarelle::{render_aquarelle_orb, AquarelleParams};
use tiny_skia::{Color, Pixmap};

let mut pix = Pixmap::new(128, 128).unwrap();
pix.fill(Color::from_rgba8(0, 0, 0, 255));

render_aquarelle_orb(
    &mut pix,
    (64.0, 64.0),       // center
    40.0,               // radius
    [200, 100, 50],     // sRGB color
    42,                 // seed (determinism)
    AquarelleParams::default(),
);

Determinism

Identical (center, radius, color, seed, params) produce byte-identical pixels. RNG state is seeded per call via ChaCha8Rng::seed_from_u64(seed) and never touches thread_rng.

Bleed pass (v0.2)

For callers that already have a rasterized image (e.g. ink lines on a white background from blueprinter) and want to bleed the existing pixels themselves, render_aquarelle_bleed_pass applies a Gaussian-approximating box blur (3 passes) to the whole pixmap with a halo saturation boost and a faint seed-derived paper-grain noise. The original picture is then re-composited on top, so the bleed reads as a halo underneath the existing strokes.

Structs

AquarelleBleedParams

Knobs for render_aquarelle_bleed_pass. All values are interpreted in their natural range and clamped internally; callers can pass raw slider values without pre-validation.

AquarelleParams

Intensities of the four aquarelle elements. Each value is interpreted in 0.0..=1.0; out-of-range inputs are clamped internally so the caller can pass raw slider values without pre-validation.

SpiralBleedParams

新「にじみ」（螺旋ブラー）の 4 軸パラメータ。各 0.0..=1.0。

Constants

AQUA_BLEED_WGSL

共有「にじみ」WGSL フラグメント（48 タップ黄金角螺旋 + bloom/halo character）。

AQUA_BLUR_TAPS

螺旋ブラーのタップ数（WGSL AQUA_BLUR_TAPS と一致）。

AQUA_GOLDEN_ANGLE

黄金角（rad、WGSL AQUA_GOLDEN_ANGLE と一致）。値は orber orb.wgsl と逐字一致させる （f32 の表現桁を超えるが WGSL/naga も同じ f32 に丸めるので値は一致＝parity）。

AQUA_OFFSET_BIAS

offset の disk 原点バイアス比（WGSL AQUA_OFFSET_BIAS）。

AQUA_TAU

2π（WGSL がホスト供給を前提とする TAU = 6.28318530718 と同一 f32）。

BLOOM_MAX

bloom が白へ寄せる上限比（WGSL BLOOM_MAX）。

HALO_SAT_GAIN

halo の彩度ゲイン係数（WGSL HALO_SAT_GAIN）。

Functions

aqua_blurred_coverage_cpu

WGSL blurred_coverage の CPU リファレンス。

aqua_character_cpu

WGSL aqua_character の CPU リファレンス（ブラー後の色味補正。各軸 0.0 で恒等）。

aqua_hash21

WGSL hash21 の CPU port。fract は v - v.floor()（f32::fract は符号付きで WGSL fract と異なるため使わない）。GPU の per-pixel ディザと同じ値を返す。

aqua_seed_dir_cpu

WGSL aqua_seed_dir の CPU port。seed から決定論的な単位方向ベクトルを返す。

render_aquarelle_bleed_pass

Apply a watercolor bleed pass to an entire pixmap.

render_aquarelle_orb

Composite one aquarelle orb onto pixmap with source-over blending.