[Entrypoints] Support Online Serving for Diffusion-only Models (#259)

Signed-off-by: Chenguang ZHENG <645327136@qq.com>
Signed-off-by: yinpe <11810305@mail.sustech.edu.cn>
Co-authored-by: yinpe <11810305@mail.sustech.edu.cn>

docs/user_guide/examples/online_serving/text_to_image.md

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+# Qwen-Image/Z-Image Online Serving
+
+Source <https://github.com/vllm-project/vllm-omni/tree/main/examples/online_serving/qwen_image>.
+
+
+This example demonstrates how to deploy Qwen-Image model for online image generation service using vLLM-Omni.
+
+## Start Server
+
+### Basic Start
+
+```bash
+vllm serve Qwen/Qwen-Image --omni --port 8091
+```
+
+### Start with Parameters
+
+
+Or use the startup script:
+
+```bash
+bash run_server.sh
+```
+
+## API Calls
+
+### Method 1: Using curl
+
+```bash
+# Basic text-to-image generation
+bash run_curl_text_to_image.sh
+
+# Or execute directly
+curl -s http://localhost:8091/v1/chat/completions \
+  -H "Content-Type: application/json" \
+  -d '{
+    "messages": [
+      {"role": "user", "content": "A beautiful landscape painting"}
+    ],
+    "extra_body": {
+      "height": 1024,
+      "width": 1024,
+      "num_inference_steps": 50,
+      "true_cfg_scale": 4.0,
+      "seed": 42
+    }
+  }' | jq -r '.choices[0].message.content[0].image_url.url' | cut -d',' -f2 | base64 -d > output.png
+```
+
+### Method 2: Using Python Client
+
+```bash
+python openai_chat_client.py --prompt "A beautiful landscape painting" --output output.png
+```
+
+### Method 3: Using Gradio Demo
+
+```bash
+python gradio_demo.py
+# Visit http://localhost:7860
+```
+
+## Request Format
+
+### Simple Text-to-Image Generation
+
+```json
+{
+  "messages": [
+    {"role": "user", "content": "A beautiful landscape painting"}
+  ]
+}
+```
+
+### Generation with Parameters
+
+Use `extra_body` to pass generation parameters:
+
+```json
+{
+  "messages": [
+    {"role": "user", "content": "A beautiful landscape painting"}
+  ],
+  "extra_body": {
+    "height": 1024,
+    "width": 1024,
+    "num_inference_steps": 50,
+    "true_cfg_scale": 4.0,
+    "seed": 42
+  }
+}
+```
+
+### Multimodal Input (Text + Structured Content)
+
+```json
+{
+  "messages": [
+    {
+      "role": "user",
+      "content": [
+        {"type": "text", "text": "A beautiful landscape painting"}
+      ]
+    }
+  ]
+}
+```
+
+## Generation Parameters (extra_body)
+
+| Parameter | Type | Default | Description |
+|-----------|------|---------|-------------|
+| `height` | int | None | Image height in pixels |
+| `width` | int | None | Image width in pixels |
+| `num_inference_steps` | int | 50 | Number of denoising steps |
+| `true_cfg_scale` | float | 4.0 | Qwen-Image CFG scale |
+| `seed` | int | None | Random seed (reproducible) |
+| `negative_prompt` | str | None | Negative prompt |
+| `num_outputs_per_prompt` | int | 1 | Number of images to generate |
+
+## Response Format
+
+```json
+{
+  "id": "chatcmpl-xxx",
+  "created": 1234567890,
+  "model": "Qwen/Qwen-Image",
+  "choices": [{
+    "index": 0,
+    "message": {
+      "role": "assistant",
+      "content": [{
+        "type": "image_url",
+        "image_url": {
+          "url": "data:image/png;base64,..."
+        }
+      }]
+    },
+    "finish_reason": "stop"
+  }],
+  "usage": {...}
+}
+```
+
+## Extract Image
+
+```bash
+# Extract base64 from response and decode to image
+cat response.json | jq -r '.choices[0].message.content[0].image_url.url' | cut -d',' -f2 | base64 -d > output.png
+```
+
+## File Description
+
+| File | Description |
+|------|-------------|
+| `run_server.sh` | Server startup script |
+| `run_curl_text_to_image.sh` | curl example |
+| `openai_chat_client.py` | Python client |
+| `gradio_demo.py` | Gradio interactive interface |
+
+## Example materials
+
+??? abstract "gradio_demo.py"
+    ``````py
+    --8<-- "examples/online_serving/qwen_image/gradio_demo.py"
+    ``````
+??? abstract "openai_chat_client.py"
+    ``````py
+    --8<-- "examples/online_serving/qwen_image/openai_chat_client.py"
+    ``````
+??? abstract "run_curl_text_to_image.sh"
+    ``````sh
+    --8<-- "examples/online_serving/qwen_image/run_curl_text_to_image.sh"
+    ``````
+??? abstract "run_server.sh"
+    ``````sh
+    --8<-- "examples/online_serving/qwen_image/run_server.sh"
+    ``````