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feat: PuLID-Flux identity-injection support
This PR adds support for [PuLID-Flux](https://github.com/ToTheBeginning/PuLID) identity preservation to the Flux denoise loop. Given a single source portrait, generated images preserve the source person's face across arbitrary scenes and prompts. ### What's included - `src/pulid.hpp` — `PuLIDPerceiverAttentionCA`, the cross-attention module mirroring the PyTorch reference at [ToTheBeginning/PuLID/.../encoders_transformer.py](https://github.com/ToTheBeginning/PuLID/blob/main/pulid/encoders_transformer.py). Pure-ggml graph; runs on CPU / CUDA / Vulkan / Metal without backend-specific code. - `src/flux.hpp` — adds 20 `pulid_ca.<i>` child blocks to `Flux` (constructed conditionally when `params.pulid_enabled` is set), inserts the cross-attention call between transformer blocks at the intervals the PyTorch reference uses (every 2nd double block, every 4th single block), and threads two new optional parameters (`pulid_id`, `pulid_id_weight`) through `forward`, `forward_orig`, `forward_chroma_radiance`, `forward_flux_chroma`, `compute`, and `build_graph`. - `src/stable-diffusion.cpp` — loads `pulid_*.safetensors` via `model_loader.init_from_file` under the existing `model.diffusion_model.` prefix so PuLID-CA tensors bind to the new blocks naturally. PuLID-encoder keys (which live in the precompute tool, not in C++) are correctly identified as unknown. Adds `load_pulid_id_embedding()` to parse a small `.pulidembd` binary file and wraps its content as a `sd::Tensor<float>` passed via `DiffusionParams`. - `include/stable-diffusion.h` — public API: `sd_pulid_params_t` (per-generation embedding path + weight), `pulid_weights_path` on `sd_ctx_params_t`, `pulid_params` on `sd_img_gen_params_t`. - `examples/common/common.{cpp,h}` — three new CLI flags: `--pulid-weights <path>`, `--pulid-id-embedding <path>`, and `--pulid-id-weight <float>`. - `src/diffusion_model.hpp` — extends `DiffusionParams` to carry the new identity embedding + weight; `FluxModel::compute` forwards both through. - `docs/pulid.md` — usage, binary format spec, supported PuLID weight versions (v0.9.0 / v0.9.1; v1.1 deferred), memory budget notes, and a three-way SHA-256 falsification recipe. - `scripts/pulid_extract_id.py` — reference precompute tool that produces the `.pulidembd` binary from a source portrait. Lives outside the C++ build because identity extraction (insightface + EVA-CLIP-L + IDFormer) is a heavy PyTorch stack that would be impractical to port to ggml just to run once per source person. ### Why split extraction from injection PuLID-Flux's identity extractor is a stack of three large PyTorch models (ArcFace face detector + EVA-CLIP-L vision encoder + IDFormer perceiver-resampler). Porting all three to C++/ggml would add ~5000 lines for code that runs once per source person and produces a 131 KB output. By making sd.cpp consume a precomputed binary file, the C++ surface area is small (~600 lines), the heavy ML stack only needs to run once per person on any backend that supports PyTorch, and adding PuLID is decoupled from the active development on insightface / EVA-CLIP / IDFormer. ### Binary format ``` offset 0 : magic "PULIDV01" (8 bytes ASCII) offset 8 : num_tokens (uint32 LE) offset 12 : token_dim (uint32 LE) offset 16 : dtype (uint8): 0=fp16, 1=bf16, 2=fp32 offset 17 : reserved zeros (15 bytes; header total = 32) offset 32 : tokens, row-major LE ``` Typical (32, 2048, fp16) = 131 KB. ### Verification The three-way SHA-256 falsification recipe in docs/pulid.md distinguishes "the feature is wired but doesn't do anything" from "the feature is actively altering the diffusion trajectory": | Run | Expected hash relation | |-----------------------------------------|--------------------------------------------| | A: no `--pulid-*` flags | baseline | | B: PuLID flags, `--pulid-id-weight 0.0` | byte-identical to A | | C: PuLID flags, `--pulid-id-weight 1.0` | differs, preserves source identity | Verified on three backends with the same source code: - **Vulkan-AMD** (RX 6700 XT, `-DSD_VULKAN=ON`): A == B byte-identical, A != C, C visually preserves source identity. - **Vulkan-NVIDIA** (RTX 3060, same binary, `--backend "diffusion=vulkan1"`): A == B, A != C, C visually equivalent to the AMD output at the same seed (different bytes per the usual cross-backend nondeterminism). - **CUDA-NVIDIA** (RTX 3060, separate `-DSD_CUDA=ON -DCMAKE_CUDA_ARCHITECTURES=86` build against CUDA 13.2): A == B byte-identical, A != C, C visually preserves source identity. PerceiverAttentionCA's pure-ggml graph code runs unchanged across all three backends -- no backend-specific conditionals were needed. Per-image sampling times at 512x512 / 4 steps / Flux Schnell Q4 + PuLID: | Backend | Sampling (s) | Notes | |------------------------|-------------:|--------------------------------| | AMD 6700 XT (Vulkan) | 22 | 12 GB consumer card | | NVIDIA 3060 (Vulkan) | 11 | same binary as AMD | | NVIDIA 3060 (CUDA) | 9.6 | separate `-DSD_CUDA=ON` build | batch_count=3 was tested separately and confirms the long-lived-worker amortization story: per-image sampling drops from 19.6 s (cold) to ~11 s (warm) as the model stays resident across batch iterations. Tested with Flux Schnell Q4_K_S + PuLID v0.9.1 at 512x512 / 4 steps, and Flux Dev Q4_K_S + PuLID v0.9.1 at 768x768 / 20 steps. 1024x1024 + Dev + PuLID OOMs on a 12 GB card unless the VAE is routed to the CPU backend via `--backend "vae=cpu"` (not just `--vae-on-cpu`, which only offloads weights, not the compute buffer); this is existing stable-diffusion.cpp behavior, not a PuLID-specific issue, but documented in docs/pulid.md because PuLID users will hit it. Tested with batch_count > 1 (verified each image gets the same identity, different composition). ### Not yet supported (called out in docs/pulid.md) - PuLID v1.1 (`pulid_v1.1.safetensors`) -- has renamed key layout (`id_adapter_attn_layers.*` vs `pulid_ca.*`) and potentially different module structure. Follow-up PR. - Multiple ID images fused into one embedding (the reference Python pipeline supports this; the current precompute tool accepts only one portrait per run). - The `--true-cfg` negative-prompt branch -- PuLID only injects on the positive conditioning path in the reference implementation; this matches. ### Backward compatibility Non-PuLID generations are unaffected. The `params.pulid_enabled` flag defaults to false and is only set when the model loader sees a `pulid_ca.*` tensor in the loaded safetensors file. A regression run of Flux Schnell Q4 without `--pulid-*` flags produces byte-identical output to pre-patch. ### File summary ``` include/stable-diffusion.h +34 / -0 src/stable-diffusion.cpp +120 / -0 src/diffusion_model.hpp +5 / -1 src/flux.hpp +106 / -10 src/pulid.hpp +127 / -0 (new) examples/common/common.h +6 / -0 examples/common/common.cpp +19 / -0 docs/pulid.md +220 / -0 (new) scripts/pulid_extract_id.py +135 / -0 (new) ``` Total ~770 added lines, ~10 changed. No removed functionality.
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docs/pulid.md

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# PuLID-Flux face-identity preservation
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stable-diffusion.cpp supports the [PuLID-Flux](https://github.com/ToTheBeginning/PuLID)
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identity-injection technique on top of Flux.1 (schnell or dev) models.
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Given a single source portrait, PuLID-Flux produces new generations that
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preserve the source person's face across arbitrary scenes, poses, and
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prompts.
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Unlike PhotoMaker (which extracts the identity inside the inference
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process from a directory of images), PuLID-Flux's identity extractor is
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a heavy stack (insightface ArcFace + EVA-CLIP-L + IDFormer encoder) that
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is impractical to port to C++/ggml. To keep this implementation small and
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cross-vendor, **stable-diffusion.cpp consumes a precomputed identity
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embedding** produced by an external Python tool that runs once per source
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portrait. Everything downstream of that one-shot extraction is C++ and
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runs on any backend (Vulkan, CUDA, Metal, ROCm, CPU).
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## Architecture summary
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The PuLID-Flux contribution to the Flux denoise loop is a stack of 20
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small cross-attention modules (`PerceiverAttentionCA`) inserted between
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the Flux transformer blocks:
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- After every 2nd of the 19 double-stream blocks (10 hook points)
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- After every 4th of the 38 single-stream blocks (10 hook points)
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Each cross-attention layer takes the current image tokens as query, the
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32-token / 2048-dim identity embedding as key+value, and adds its output
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(scaled by `id_weight`, typically 1.0) back to the image tokens.
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## Required weights
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Three files in addition to the standard Flux weight set:
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1. **Flux base** (transformer + VAE + clip_l + t5xxl) -- exactly as
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[docs/flux.md](flux.md) describes.
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2. **PuLID weights** -- download from
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[guozinan/PuLID](https://huggingface.co/guozinan/PuLID):
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- `pulid_flux_v0.9.0.safetensors` or `pulid_flux_v0.9.1.safetensors`
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(recommended; this implementation is verified against v0.9.1)
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- **v1.1 (`pulid_v1.1.safetensors`) is NOT yet supported** -- it uses
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renamed keys (`id_adapter_attn_layers.*` instead of `pulid_ca.*`)
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and possibly different module structure. Future PR.
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3. **Identity embedding (.pulidembd)** -- produced by the precompute
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tool below.
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## Precompute the identity embedding
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The precompute tool runs the PyTorch identity-extraction stack on a
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single portrait image and writes the resulting `(32, 2048)` embedding
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to a `.pulidembd` binary file (about 131 KB). Run it once per source
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person; the same file is reused for any number of generations.
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A reference Python script is provided alongside this docs file at
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[`scripts/pulid_extract_id.py`](../scripts/pulid_extract_id.py). It
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requires:
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- A working CUDA / CPU PyTorch + diffusers stack
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- `insightface`, `facexlib`, `eva-clip`, `torchvision`
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- The PuLID weights file (same one stable-diffusion.cpp will load below)
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- The ToTheBeginning/PuLID repo's `pulid/pipeline_flux.py` (and its
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dependencies under `pulid/` and `flux/`) -- recommended to vendor
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rather than pip-install due to upstream packaging quirks
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Run it as:
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```
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python pulid_extract_id.py \
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--portrait /path/to/source-photo.jpg \
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--pulid-weights /path/to/pulid_flux_v0.9.1.safetensors \
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--out /path/to/source.pulidembd
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```
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## Binary format (.pulidembd)
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```
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offset 0 : magic "PULIDV01" (8 bytes ASCII)
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offset 8 : num_tokens (uint32 LE) typically 32
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offset 12 : token_dim (uint32 LE) typically 2048
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offset 16 : dtype (uint8): 0=fp16, 1=bf16, 2=fp32
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offset 17 : reserved zeros (15 bytes; header total = 32)
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offset 32 : tokens, row-major LE (num_tokens * token_dim values)
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```
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stable-diffusion.cpp parses the header, validates the magic, and converts
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to fp32 at load time. Total file size for the typical (32, 2048, fp16)
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case is 131 KB.
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## Command-line usage
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```
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.\bin\Release\sd-cli.exe \
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--diffusion-model models\flux1-schnell-Q4_K_S.gguf \
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--vae models\ae.safetensors \
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--clip_l models\clip_l.safetensors \
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--t5xxl models\t5xxl_fp16.safetensors \
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--pulid-weights models\pulid_flux_v0.9.1.safetensors \
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--pulid-id-embedding source.pulidembd \
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--pulid-id-weight 1.0 \
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-p "candid photograph of a young woman on a beach at sunset" \
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--cfg-scale 1.0 --sampling-method euler --steps 4 -W 512 -H 512 \
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--seed 42 --clip-on-cpu \
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-o out.png
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```
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For Flux Dev (instead of Schnell), add `--guidance 3.5` and `--steps 20`.
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## Flags
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| Flag | Purpose |
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|----------------------------|-------------------------------------------------------------------|
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| `--pulid-weights <path>` | Path to `pulid_flux_v0.9.x.safetensors`. Loaded with the model. |
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| `--pulid-id-embedding <p>` | Path to a `.pulidembd` binary produced by the precompute tool. |
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| `--pulid-id-weight <f>` | Identity-injection strength. Typical 0.7-1.2; default 1.0. |
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All three flags must be set together to activate PuLID. Setting only
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`--pulid-weights` (no embedding) loads the weights but disables injection
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at runtime. Setting `--pulid-id-weight 0` zeros out the contribution
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(useful for falsification testing: outputs should be byte-identical to
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a no-PuLID run with the same seed).
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## Memory budget
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At 512x512, 4 steps (Schnell), the 20 cross-attention layers add roughly
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10% to denoise time and almost nothing to peak VRAM. Tested on a 12 GB
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consumer card alongside Flux Schnell Q4 GGUF + CPU-offloaded clip_l and
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t5xxl + GPU-resident VAE.
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At 1024x1024 with Flux Dev Q4 + 20 steps + PuLID, the VAE decode compute
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buffer doesn't fit on a 12 GB card even with `--vae-on-cpu`. Workaround:
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explicitly route VAE to the CPU backend instead of the offload flag:
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```
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--backend "diffusion=vulkan0,vae=cpu"
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```
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The `--vae-on-cpu` flag offloads VAE weights but leaves the compute graph
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on the default backend; this is existing stable-diffusion.cpp behavior,
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not a PuLID-specific issue. Documented here because anyone running PuLID
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at 1024 will hit it.
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## Backend selection
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The standard `--backend` flag works as documented. Common patterns:
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```
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# AMD Vulkan
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--backend "diffusion=vulkan0,vae=cpu"
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# NVIDIA Vulkan
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--backend "diffusion=vulkan1,vae=cpu"
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# CUDA
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--backend "diffusion=cuda0,vae=cpu"
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```
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The PuLID cross-attention layers run on the same backend as the main
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diffusion model. They have not yet been independently profiled on every
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backend; only Vulkan and CPU have been tested by the original contributor.
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## Verification
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A three-way SHA-256 check is the recommended sanity test when bringing up
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a new combination of model + backend + hardware:
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| Run | Expected hash relation |
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|----------------------------------------------|------------------------------------|
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| A: no `--pulid-*` flags | baseline |
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| B: PuLID flags, `--pulid-id-weight 0.0` | **byte-identical to A** |
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| C: PuLID flags, `--pulid-id-weight 1.0` | **different from A,B**, preserves source identity |
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If A and C differ but A and B differ too, the injection is allocating
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or computing something even at zero weight -- likely a bug.
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## Limitations / not yet supported
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- **`--skip-layers` (skip-layer-guidance / SLG) combined with PuLID** is not
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supported. The `pulid_ca` index advances per non-skipped block, so a
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skipped block silently misaligns the cross-attention weight assignment
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vs. the trained intervals. The reference PyTorch implementation does
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not have SLG either, so there is no well-defined behavior to emulate.
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Use either feature alone.
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- **PuLID v1.1 weights** (`pulid_v1.1.safetensors`, renamed key layout).
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- **Multiple ID images.** The reference PyTorch implementation can fuse
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several portraits into one embedding for stronger identity. This
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implementation accepts a single embedding produced from one or more
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images by the external precompute tool.
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- **Negative-prompt branch of CFG.** PuLID only injects on the positive
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conditioning path in the published reference, and the implementation
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here follows that. Flux's distilled guidance doesn't run a separate
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uncond branch in normal use, so this matters only for `--true-cfg`
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workflows that aren't standard for Flux.
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- **Backends other than Vulkan and CPU** are untested by the original
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contributor. The implementation is pure-ggml and should work on CUDA,
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ROCm, and Metal, but verification by users on those backends is
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welcomed.

examples/common/common.cpp

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"--photo-maker",
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"path to PHOTOMAKER model",
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&photo_maker_path},
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{"",
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"--pulid-weights",
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"path to PuLID flux weights (e.g. pulid_flux_v0.9.1.safetensors). Identity is injected during the denoise loop when paired with --pulid-id-embedding.",
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&pulid_weights_path},
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{"",
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"--upscale-model",
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"path to esrgan model.",
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embedding_vec.data(),
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static_cast<uint32_t>(embedding_vec.size()),
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photo_maker_path.c_str(),
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pulid_weights_path.c_str(),
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tensor_type_rules.c_str(),
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vae_decode_only,
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free_params_immediately,
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"--pm-id-embed-path",
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"path to PHOTOMAKER v2 id embed",
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&pm_id_embed_path},
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{"",
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"--pulid-id-embedding",
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"path to a .pulidembd binary produced by pulid_extract_id.py. Carries a (32, 2048) identity embedding extracted from a source portrait. Pair with --pulid-weights on the context.",
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&pulid_id_embedding_path},
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{"",
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"--hires-upscaler",
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"highres fix upscaler, Lanczos, Nearest, Latent, Latent (nearest), Latent (nearest-exact), "
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"--pm-style-strength",
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"",
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&pm_style_strength},
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{"",
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"--pulid-id-weight",
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"strength of PuLID identity injection (default: 1.0). 0.7-1.2 are typical; lower lets the prompt override the face more, higher tightens identity match.",
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&pulid_id_weight},
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{"",
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"--control-strength",
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"strength to apply Control Net (default: 0.9). 1.0 corresponds to full destruction of information in init image",
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pm_style_strength,
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};
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sd_pulid_params_t pulid_params = {
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pulid_id_embedding_path.empty() ? nullptr : pulid_id_embedding_path.c_str(),
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pulid_id_weight,
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};
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params.loras = lora_vec.empty() ? nullptr : lora_vec.data();
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params.lora_count = static_cast<uint32_t>(lora_vec.size());
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params.prompt = prompt.c_str();
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params.control_image = control_image.get();
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params.control_strength = control_strength;
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params.pm_params = pm_params;
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params.pulid_params = pulid_params;
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params.vae_tiling_params = vae_tiling_params;
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params.cache = cache_params;
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examples/common/common.h

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std::string control_net_path;
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std::string embedding_dir;
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std::string photo_maker_path;
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// PuLID-Flux identity-preservation context path: the safetensors blob
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// carrying the PerceiverAttentionCA cross-attention weights. Loaded
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// once with the model. Per-generation pulid_id_embedding_path lives in
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// SDGenerationParams below.
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std::string pulid_weights_path;
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sd_type_t wtype = SD_TYPE_COUNT;
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std::string tensor_type_rules;
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std::string lora_model_dir = ".";
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std::string pm_id_embed_path;
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float pm_style_strength = 20.f;
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// PuLID-Flux: per-generation identity embedding (binary file produced by
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// runtime-scripts/pulid_extract_id.py). Format documented in
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// include/stable-diffusion.h sd_pulid_params_t.
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std::string pulid_id_embedding_path;
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float pulid_id_weight = 1.0f;
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int upscale_repeats = 1;
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int upscale_tile_size = 128;
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include/stable-diffusion.h

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const sd_embedding_t* embeddings;
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uint32_t embedding_count;
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const char* photo_maker_path;
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/**
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* Path to pulid_flux_v0.9.1.safetensors (the PuLID identity-injection
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* cross-attention weights). When set together with sd_img_gen_params_t.
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* pulid_params.id_embedding_path, the Flux diffusion model performs PuLID
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* cross-attention injection during the denoise loop. Loaded once with
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* the model; the embedding is per-generation. Currently only meaningful
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* for Flux (depth=19 double, 38 single blocks); silently ignored for
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* other model versions.
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*/
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const char* pulid_weights_path;
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const char* tensor_type_rules;
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bool vae_decode_only;
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bool free_params_immediately;
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float style_strength;
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} sd_pm_params_t; // photo maker
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/**
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* PuLID-Flux identity preservation params.
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*
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* Unlike PhotoMaker (which extracts the ID embedding inside the inference
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* process from a directory of images), PuLID's ID extraction is a heavy
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* Python-only stack (insightface ArcFace + EVA-CLIP-L + IDFormer). To stay
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* cross-vendor in C++/Vulkan, sd.cpp consumes a precomputed binary file
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* produced by an external tool (runtime-scripts/pulid_extract_id.py in the
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* Cloudhands client tree).
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*
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* Binary format (.pulidembd):
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* offset 0 : magic "PULIDV01" (8 bytes ASCII)
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* offset 8 : num_tokens (uint32 LE)
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* offset 12 : token_dim (uint32 LE)
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* offset 16 : dtype (uint8): 0=fp16, 1=bf16, 2=fp32
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* offset 17 : reserved zeros (15 bytes; header = 32 bytes total)
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* offset 32 : tokens, row-major LE (num_tokens * token_dim values)
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*/
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typedef struct {
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const char* id_embedding_path; // path to .pulidembd file produced by pulid_extract_id.py
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float id_weight; // strength of the ID injection; typical 0.7-1.2, default 1.0
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} sd_pulid_params_t;
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enum sd_cache_mode_t {
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SD_CACHE_DISABLED = 0,
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SD_CACHE_EASYCACHE,
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sd_image_t control_image;
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float control_strength;
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sd_pm_params_t pm_params;
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sd_pulid_params_t pulid_params;
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sd_tiling_params_t vae_tiling_params;
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sd_cache_params_t cache;
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sd_hires_params_t hires;

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