Improve docs related to dynamic T5 sequence length selection.

invokeai/app/invocations/flux_text_encoder.py

@@ -29,7 +29,7 @@ from invokeai.backend.stable_diffusion.diffusion.conditioning_data import Condit
     title="FLUX Text Encoding",
     tags=["prompt", "conditioning", "flux"],
     category="conditioning",
-    version="1.1.0",
+    version="1.2.0",
     classification=Classification.Prototype,
 )
 class FluxTextEncoderInvocation(BaseInvocation):
@@ -48,6 +48,11 @@ class FluxTextEncoderInvocation(BaseInvocation):
     t5_max_seq_len: Literal[256, 512] = InputField(
         description="Max sequence length for the T5 encoder. Expected to be 256 for FLUX schnell models and 512 for FLUX dev models."
     )
+    use_short_t5_seq_len: bool = InputField(
+        description="Use a shorter sequence length for the T5 encoder if a short prompt is used. This can improve "
+        + "performance and reduce peak memory, but may result in slightly different image outputs.",
+        default=True,
+    )
     prompt: str = InputField(description="Text prompt to encode.", ui_component=UIComponent.Textarea)
     mask: Optional[TensorField] = InputField(
         default=None, description="A mask defining the region that this conditioning prompt applies to."
@@ -74,6 +79,12 @@ class FluxTextEncoderInvocation(BaseInvocation):
 
         prompt = [self.prompt]
 
+        valid_seq_lens = [self.t5_max_seq_len]
+        if self.use_short_t5_seq_len:
+            # We allow a minimum sequence length of 128. Going too short results in more significant image chagnes.
+            valid_seq_lens = list(range(128, self.t5_max_seq_len, 128))
+            valid_seq_lens.append(self.t5_max_seq_len)
+
         with (
             t5_text_encoder_info as t5_text_encoder,
             t5_tokenizer_info as t5_tokenizer,
@@ -81,10 +92,10 @@ class FluxTextEncoderInvocation(BaseInvocation):
             assert isinstance(t5_text_encoder, T5EncoderModel)
             assert isinstance(t5_tokenizer, T5Tokenizer)
 
-            t5_encoder = HFEncoder(t5_text_encoder, t5_tokenizer, False, self.t5_max_seq_len)
+            t5_encoder = HFEncoder(t5_text_encoder, t5_tokenizer, False)
 
             context.util.signal_progress("Running T5 encoder")
-            prompt_embeds = t5_encoder(prompt)
+            prompt_embeds = t5_encoder(prompt, valid_seq_lens)
 
         assert isinstance(prompt_embeds, torch.Tensor)
         return prompt_embeds
@@ -122,10 +133,10 @@ class FluxTextEncoderInvocation(BaseInvocation):
                 # There are currently no supported CLIP quantized models. Add support here if needed.
                 raise ValueError(f"Unsupported model format: {clip_text_encoder_config.format}")
 
-            clip_encoder = HFEncoder(clip_text_encoder, clip_tokenizer, True, 77)
+            clip_encoder = HFEncoder(clip_text_encoder, clip_tokenizer, True)
 
             context.util.signal_progress("Running CLIP encoder")
-            pooled_prompt_embeds = clip_encoder(prompt)
+            pooled_prompt_embeds = clip_encoder(prompt, [77])
 
         assert isinstance(pooled_prompt_embeds, torch.Tensor)
         return pooled_prompt_embeds

invokeai/backend/flux/modules/conditioner.py

@@ -1,32 +1,53 @@
 # Initially pulled from https://github.com/black-forest-labs/flux
 
+
 from torch import Tensor, nn
 from transformers import PreTrainedModel, PreTrainedTokenizer
 
 
 class HFEncoder(nn.Module):
-    def __init__(self, encoder: PreTrainedModel, tokenizer: PreTrainedTokenizer, is_clip: bool, max_length: int):
+    def __init__(self, encoder: PreTrainedModel, tokenizer: PreTrainedTokenizer, is_clip: bool):
         super().__init__()
-        self.max_length = max_length
         self.is_clip = is_clip
         self.output_key = "pooler_output" if self.is_clip else "last_hidden_state"
         self.tokenizer = tokenizer
         self.hf_module = encoder
         self.hf_module = self.hf_module.eval().requires_grad_(False)
 
-    def forward(self, text: list[str]) -> Tensor:
+    def forward(self, text: list[str], valid_seq_lens: list[int]) -> Tensor:
+        """Encode text into a tensor.
+
+        Args:
+            text: A list of text prompts to encode.
+            valid_seq_lens: A list of valid sequence lengths. The shortest valid sequence length that can contain the
+                text will be used. If the largest valid sequence length cannot contain the text, the encoding will be
+                truncated.
+        """
+        valid_seq_lens = sorted(valid_seq_lens)
+
+        # Perform initial encoding with the maximum valid sequence length.
         batch_encoding = self.tokenizer(
             text,
             truncation=True,
-            max_length=self.max_length,
-            return_length=False,
+            max_length=max(valid_seq_lens),
+            return_length=True,
             return_overflowing_tokens=False,
             padding="max_length",
             return_tensors="pt",
         )
 
+        # Find selected_seq_len, the minimum valid sequence length that can contain all of the input tokens.
+        seq_len: int = batch_encoding["length"][0].item()
+        selected_seq_len = valid_seq_lens[-1]
+        for len in valid_seq_lens:
+            if len >= seq_len:
+                selected_seq_len = len
+                break
+
+        input_ids = batch_encoding["input_ids"][..., :selected_seq_len]
+
         outputs = self.hf_module(
-            input_ids=batch_encoding["input_ids"].to(self.hf_module.device),
+            input_ids=input_ids.to(self.hf_module.device),
             attention_mask=None,
             output_hidden_states=False,
         )