sd_sample_stepwise: Run the sampling loop step-by-step in R (low-level)

In sd2R: Stable Diffusion Image Generation

Run the sampling loop step-by-step in R (low-level)

Description

Equivalent to sd_sample for the Euler / Euler-a samplers, but runs the loop in R so a callback can observe or interrupt each step (e.g. live preview). For Euler (no ancestral noise) the result is bit-for-bit equal to sd_sample; Euler-a differs (R RNG vs ggml RNG for the ancestral term). Other samplers are not supported here — use sd_sample.

Usage

sd_sample_stepwise(
  ctx,
  cond,
  uncond = list(crossattn = NULL, vector = NULL, concat = NULL),
  latent_shape = NULL,
  init_latent = NULL,
  noise = NULL,
  width = 512L,
  height = 512L,
  sample_method = SAMPLE_METHOD$EULER,
  scheduler = SCHEDULER$DISCRETE,
  sample_steps = 20L,
  cfg_scale = 7,
  seed = 42L,
  custom_sigmas = NULL,
  on_step = NULL
)

Arguments

ctx	SD context
cond	Positive conditioning from sd_encode_text
uncond	Negative conditioning; empty (all NULL) disables CFG
latent_shape	Integer c(W, H, C) in latent space, used to make noise when noise is NULL
init_latent	Optional starting latent (img2img); NULL for txt2img
noise	Optional explicit noise sd_tensor; generated from seed and latent_shape when NULL
width, height	Generation size in PIXELS (for the sigma schedule)
sample_method	SAMPLE_METHOD$EULER or $EULER_A
scheduler	Scheduler (name or SCHEDULER value)
sample_steps	Number of steps
cfg_scale	CFG scale
seed	Seed for noise generation when noise is NULL
custom_sigmas	Optional explicit sigma schedule (overrides scheduler)
on_step	Optional callback function(step, total, x, denoised) called after each step; return FALSE to stop early.

Value

An sd_tensor — the denoised latent x_0.

See Also

sd_sample, sd_decode_latent

sd2R documentation built on June 19, 2026, 9:08 a.m.