inference_colab.py

# ============================================================================
# TinyFlux Inference Cell - Euler Discrete Flow Matching
# ============================================================================
# Run the model cell before this one (defines TinyFlux, TinyFluxConfig)
# Loads from: AbstractPhil/tiny-flux or local checkpoint
# ============================================================================

import torch
from huggingface_hub import hf_hub_download
from safetensors.torch import load_file
from transformers import T5EncoderModel, T5Tokenizer, CLIPTextModel, CLIPTokenizer
from diffusers import AutoencoderKL
from PIL import Image
import numpy as np
import os

# ============================================================================
# CONFIG
# ============================================================================
DEVICE = "cuda"
DTYPE = torch.bfloat16 if torch.cuda.is_bf16_supported() else torch.float16

# Model loading
HF_REPO = "AbstractPhil/tiny-flux"
LOAD_FROM = "hub"  # "hub", "hub:step_1000", "local:/path/to/weights.safetensors"

# Generation settings
NUM_STEPS = 20          # Euler steps (20-50 typical)
GUIDANCE_SCALE = 3.5    # CFG scale (1.0 = no guidance, 3-7 typical)
HEIGHT = 512            # Output height
WIDTH = 512             # Output width
SEED = None             # None for random

# ============================================================================
# LOAD TEXT ENCODERS
# ============================================================================
print("Loading text encoders...")
t5_tok = T5Tokenizer.from_pretrained("google/flan-t5-base")
t5_enc = T5EncoderModel.from_pretrained("google/flan-t5-base", torch_dtype=DTYPE).to(DEVICE).eval()

clip_tok = CLIPTokenizer.from_pretrained("openai/clip-vit-large-patch14")
clip_enc = CLIPTextModel.from_pretrained("openai/clip-vit-large-patch14", torch_dtype=DTYPE).to(DEVICE).eval()

# ============================================================================
# LOAD VAE
# ============================================================================
print("Loading Flux VAE...")
vae = AutoencoderKL.from_pretrained(
    "black-forest-labs/FLUX.1-schnell",
    subfolder="vae",
    torch_dtype=DTYPE
).to(DEVICE).eval()

# ============================================================================
# LOAD TINYFLUX MODEL
# ============================================================================
print(f"Loading TinyFlux from: {LOAD_FROM}")

config = TinyFluxConfig()
model = TinyFlux(config).to(DEVICE).to(DTYPE)

if LOAD_FROM == "hub":
    # Load best model from hub
    weights_path = hf_hub_download(repo_id=HF_REPO, filename="model.safetensors")
    weights = load_file(weights_path)
    model.load_state_dict(weights)
    print(f"✓ Loaded from {HF_REPO}/model.safetensors")
elif LOAD_FROM.startswith("hub:"):
    # Load specific checkpoint from hub
    ckpt_name = LOAD_FROM[4:]
    if not ckpt_name.endswith(".safetensors"):
        ckpt_name = f"checkpoints/{ckpt_name}.safetensors"
    weights_path = hf_hub_download(repo_id=HF_REPO, filename=ckpt_name)
    weights = load_file(weights_path)
    model.load_state_dict(weights)
    print(f"✓ Loaded from {HF_REPO}/{ckpt_name}")
elif LOAD_FROM.startswith("local:"):
    # Load local file
    weights_path = LOAD_FROM[6:]
    weights = load_file(weights_path)
    model.load_state_dict(weights)
    print(f"✓ Loaded from {weights_path}")
else:
    raise ValueError(f"Unknown LOAD_FROM: {LOAD_FROM}")

model.eval()
print(f"Model params: {sum(p.numel() for p in model.parameters()):,}")

# ============================================================================
# ENCODING FUNCTIONS
# ============================================================================
@torch.no_grad()
def encode_prompt(prompt: str, max_length: int = 128):
    """Encode prompt with flan-t5-base and CLIP-L."""
    # T5 encoding (sequence)
    t5_in = t5_tok(
        prompt, 
        max_length=max_length, 
        padding="max_length", 
        truncation=True, 
        return_tensors="pt"
    ).to(DEVICE)
    t5_out = t5_enc(
        input_ids=t5_in.input_ids, 
        attention_mask=t5_in.attention_mask
    ).last_hidden_state  # (1, L, 768)
    
    # CLIP encoding (pooled)
    clip_in = clip_tok(
        prompt, 
        max_length=77, 
        padding="max_length", 
        truncation=True, 
        return_tensors="pt"
    ).to(DEVICE)
    clip_out = clip_enc(
        input_ids=clip_in.input_ids, 
        attention_mask=clip_in.attention_mask
    )
    clip_pooled = clip_out.pooler_output  # (1, 768)
    
    return t5_out, clip_pooled

# ============================================================================
# EULER DISCRETE FLOW MATCHING SAMPLER
# ============================================================================
@torch.no_grad()
def euler_sample(
    model,
    prompt: str,
    negative_prompt: str = "",
    num_steps: int = 20,
    guidance_scale: float = 3.5,
    height: int = 512,
    width: int = 512,
    seed: int = None,
):
    """
    Euler discrete sampler for flow matching.
    
    Flow matching formulation:
        x_t = (1 - t) * x_0 + t * x_1
        where x_0 = noise, x_1 = data
        velocity v = x_1 - x_0 = data - noise
        
    Sampling (t: 0 -> 1, noise -> data):
        x_{t+dt} = x_t + v_pred * dt
    
    With Flux shift for improved sampling distribution.
    """
    # Set seed
    if seed is not None:
        torch.manual_seed(seed)
        generator = torch.Generator(device=DEVICE).manual_seed(seed)
    else:
        generator = None
    
    # Latent dimensions (VAE downscales by 8)
    H_lat = height // 8  # 64 for 512
    W_lat = width // 8   # 64 for 512
    C_lat = 16           # Flux VAE channels
    
    # Encode prompts
    t5_cond, clip_cond = encode_prompt(prompt)
    if guidance_scale > 1.0 and negative_prompt is not None:
        t5_uncond, clip_uncond = encode_prompt(negative_prompt)
    else:
        t5_uncond, clip_uncond = None, None
    
    # Start from pure noise (t=0 in flow matching convention)
    # Shape: (1, H*W, C)
    x = torch.randn(1, H_lat * W_lat, C_lat, device=DEVICE, dtype=DTYPE, generator=generator)
    
    # Create image position IDs for RoPE
    img_ids = TinyFlux.create_img_ids(1, H_lat, W_lat, DEVICE)
    
    # Timesteps: 0 -> 1 (noise -> data)
    # We use uniform spacing, model handles flux shift internally for training
    # For inference, linear timesteps work well
    timesteps = torch.linspace(0, 1, num_steps + 1, device=DEVICE, dtype=DTYPE)
    
    print(f"Sampling with {num_steps} Euler steps...")
    
    for i in range(num_steps):
        t_curr = timesteps[i]
        t_next = timesteps[i + 1]
        dt = t_next - t_curr
        
        t_batch = t_curr.unsqueeze(0)  # (1,)
        
        # Guidance embedding (used during training with random values 1-5)
        guidance_embed = torch.tensor([guidance_scale], device=DEVICE, dtype=DTYPE)
        
        # Conditional prediction
        v_cond = model(
            hidden_states=x,
            encoder_hidden_states=t5_cond,
            pooled_projections=clip_cond,
            timestep=t_batch,
            img_ids=img_ids,
            guidance=guidance_embed,
        )
        
        # Classifier-free guidance
        if guidance_scale > 1.0 and t5_uncond is not None:
            v_uncond = model(
                hidden_states=x,
                encoder_hidden_states=t5_uncond,
                pooled_projections=clip_uncond,
                timestep=t_batch,
                img_ids=img_ids,
                guidance=guidance_embed,
            )
            v = v_uncond + guidance_scale * (v_cond - v_uncond)
        else:
            v = v_cond
        
        # Euler step: x_{t+dt} = x_t + v * dt
        x = x + v * dt
        
        if (i + 1) % 5 == 0 or i == num_steps - 1:
            print(f"  Step {i+1}/{num_steps}, t={t_next.item():.3f}")
    
    # Reshape to image format: (1, H*W, C) -> (1, C, H, W)
    latents = x.reshape(1, H_lat, W_lat, C_lat).permute(0, 3, 1, 2)
    
    return latents

# ============================================================================
# DECODE LATENTS TO IMAGE
# ============================================================================
@torch.no_grad()
def decode_latents(latents):
    """Decode VAE latents to PIL Image."""
    # Flux VAE scaling
    latents = latents / vae.config.scaling_factor
    
    # Decode
    image = vae.decode(latents.float()).sample
    
    # Normalize to [0, 1]
    image = (image / 2 + 0.5).clamp(0, 1)
    
    # To PIL
    image = image[0].permute(1, 2, 0).cpu().numpy()
    image = (image * 255).astype(np.uint8)
    
    return Image.fromarray(image)

# ============================================================================
# MAIN GENERATION FUNCTION
# ============================================================================
def generate(
    prompt: str,
    negative_prompt: str = "",
    num_steps: int = NUM_STEPS,
    guidance_scale: float = GUIDANCE_SCALE,
    height: int = HEIGHT,
    width: int = WIDTH,
    seed: int = SEED,
    save_path: str = None,
):
    """
    Generate an image from a text prompt.
    
    Args:
        prompt: Text description of desired image
        negative_prompt: What to avoid (empty string for none)
        num_steps: Number of Euler steps (20-50)
        guidance_scale: CFG scale (1.0=none, 3-7 typical)
        height: Output height in pixels (must be divisible by 8)
        width: Output width in pixels (must be divisible by 8)
        seed: Random seed (None for random)
        save_path: Path to save image (None to skip saving)
    
    Returns:
        PIL.Image
    """
    print(f"\nGenerating: '{prompt}'")
    print(f"Settings: {num_steps} steps, cfg={guidance_scale}, {width}x{height}, seed={seed}")
    
    # Sample latents
    latents = euler_sample(
        model=model,
        prompt=prompt,
        negative_prompt=negative_prompt,
        num_steps=num_steps,
        guidance_scale=guidance_scale,
        height=height,
        width=width,
        seed=seed,
    )
    
    # Decode to image
    print("Decoding latents...")
    image = decode_latents(latents)
    
    # Save if requested
    if save_path:
        image.save(save_path)
        print(f"✓ Saved to {save_path}")
    
    print("✓ Done!")
    return image

# ============================================================================
# BATCH GENERATION
# ============================================================================
def generate_batch(
    prompts: list,
    negative_prompt: str = "",
    num_steps: int = NUM_STEPS,
    guidance_scale: float = GUIDANCE_SCALE,
    height: int = HEIGHT,
    width: int = WIDTH,
    seed: int = SEED,
    output_dir: str = "./outputs",
):
    """Generate multiple images."""
    os.makedirs(output_dir, exist_ok=True)
    images = []
    
    for i, prompt in enumerate(prompts):
        # Increment seed for variety if seed is set
        img_seed = seed + i if seed is not None else None
        
        image = generate(
            prompt=prompt,
            negative_prompt=negative_prompt,
            num_steps=num_steps,
            guidance_scale=guidance_scale,
            height=height,
            width=width,
            seed=img_seed,
            save_path=os.path.join(output_dir, f"{i:03d}.png"),
        )
        images.append(image)
    
    return images

# ============================================================================
# QUICK TEST
# ============================================================================
if __name__ == "__main__" or True:  # Always run in Colab
    print("\n" + "="*60)
    print("TinyFlux Inference Ready!")
    print("="*60)
    print(f"""
Usage:
    # Single image
    image = generate("a photo of a cat")
    image.show()
    
    # With options
    image = generate(
        prompt="a beautiful sunset over mountains",
        negative_prompt="blurry, low quality",
        num_steps=30,
        guidance_scale=4.0,
        height=512,
        width=512,
        seed=42,
        save_path="output.png"
    )
    
    # Batch generation
    images = generate_batch([
        "a red sports car",
        "a blue ocean wave", 
        "a green forest path",
    ], output_dir="./my_outputs")
""")