[Model][Qwen3VL] Use `mm_position` to compute mrope positions (#28730)

Signed-off-by: Lukas Geiger <lukas.geiger94@gmail.com>
Co-authored-by: Cyrus Leung <tlleungac@connect.ust.hk>

vllm/model_executor/models/qwen3_vl.py

@@ -24,7 +24,7 @@
 # limitations under the License.
 """Inference-only Qwen3VL model compatible with HuggingFace weights."""
 
-from collections.abc import Callable, Iterable, Mapping, Sequence
+from collections.abc import Callable, Iterable, Iterator, Mapping, Sequence
 from functools import partial
 from itertools import islice
 from typing import Any
@@ -1412,72 +1412,47 @@ class Qwen3VLForConditionalGeneration(
                 )
         return mm_input_by_modality
 
+    def iter_mm_grid_hw(
+        self, input_tokens: list[int], mm_features: list[MultiModalFeatureSpec]
+    ) -> Iterator[tuple[int, int, int]]:
+        video_token_id = self.config.video_token_id
+        spatial_merge_size = self.config.vision_config.spatial_merge_size
+        for mm_feature in sorted(mm_features, key=lambda f: f.mm_position.offset):
+            offset = mm_feature.mm_position.offset
+            if mm_feature.modality == "image":
+                t, h, w = mm_feature.data["image_grid_thw"].data.tolist()
+                assert t == 1, f"Image must have 1 frame, got {t}"
+                yield offset, h // spatial_merge_size, w // spatial_merge_size
+            elif mm_feature.modality == "video":
+                t, h, w = mm_feature.data["video_grid_thw"].data.tolist()
+                llm_grid_h = h // spatial_merge_size
+                llm_grid_w = w // spatial_merge_size
+                for _ in range(t):
+                    offset = input_tokens.index(video_token_id, offset)
+                    yield offset, llm_grid_h, llm_grid_w
+                    offset += llm_grid_h * llm_grid_w
+            else:
+                raise ValueError(f"Unsupported modality: {mm_feature.modality}")
+
     def get_mrope_input_positions(
         self,
         input_tokens: list[int],
         mm_features: list[MultiModalFeatureSpec],
     ) -> tuple[torch.Tensor, int]:
-        kwargs = MultiModalFeatureSpec.gather_kwargs(
-            mm_features,
-            {"image_grid_thw", "video_grid_thw"},
-        )
-        image_grid_thw = [item.tolist() for item in kwargs.get("image_grid_thw", [])]
-        video_grid_thw = [item.tolist() for item in kwargs.get("video_grid_thw", [])]
-
-        video_grid_thw = [[1, h, w] for t, h, w in video_grid_thw for _ in range(t)]
-
-        hf_config = self.config
-        image_token_id = hf_config.image_token_id
-        video_token_id = hf_config.video_token_id
-        vision_start_token_id = hf_config.vision_start_token_id
-        spatial_merge_size = hf_config.vision_config.spatial_merge_size
-
-        input_tokens_array = np.array(input_tokens)
-        vision_start_mask = input_tokens_array == vision_start_token_id
-        vision_tokens = input_tokens_array[vision_start_mask.nonzero()[0] + 1]
-        image_nums = np.count_nonzero(vision_tokens == image_token_id)
-        video_nums = np.count_nonzero(vision_tokens == video_token_id)
-        llm_pos_ids_list: list = []
-
+        llm_pos_ids_list = []
         st = 0
-        remain_images, remain_videos = image_nums, video_nums
-
-        image_index, video_index = 0, 0
-        for _ in range(image_nums + video_nums):
-            if image_token_id in input_tokens and remain_images > 0:
-                ed_image = input_tokens.index(image_token_id, st)
-            else:
-                ed_image = len(input_tokens) + 1
-            if video_token_id in input_tokens and remain_videos > 0:
-                ed_video = input_tokens.index(video_token_id, st)
-            else:
-                ed_video = len(input_tokens) + 1
-            if ed_image < ed_video:
-                t, h, w = image_grid_thw[image_index]
-                image_index += 1
-                remain_images -= 1
-                ed = ed_image
-            else:
-                t, h, w = video_grid_thw[video_index]
-                video_index += 1
-                remain_videos -= 1
-                ed = ed_video
-
-            llm_grid_t, llm_grid_h, llm_grid_w = (
-                t,
-                h // spatial_merge_size,
-                w // spatial_merge_size,
-            )
-            text_len = ed - st
-
+        for offset, llm_grid_h, llm_grid_w in self.iter_mm_grid_hw(
+            input_tokens, mm_features
+        ):
+            text_len = offset - st
             st_idx = llm_pos_ids_list[-1].max() + 1 if len(llm_pos_ids_list) > 0 else 0
             llm_pos_ids_list.append(
                 np.broadcast_to(np.arange(text_len), (3, text_len)) + st_idx
             )
 
-            grid_indices = np.indices((llm_grid_t, llm_grid_h, llm_grid_w))
-            llm_pos_ids_list.append(grid_indices.reshape(3, -1) + text_len + st_idx)
-            st = ed + llm_grid_t * llm_grid_h * llm_grid_w
+            grid_indices = np.indices((1, llm_grid_h, llm_grid_w)).reshape(3, -1)
+            llm_pos_ids_list.append(grid_indices + text_len + st_idx)
+            st = offset + llm_grid_h * llm_grid_w
 
         if st < len(input_tokens):
             st_idx = llm_pos_ids_list[-1].max() + 1 if len(llm_pos_ids_list) > 0 else 0