fixed webcam demo (#2596)

* fixed webcam demo

* fixed show=True

* add warning when show=False and out_file=None

demo/webcam_demo.py

@@ -3,7 +3,7 @@ import argparse
 import cv2
 import torch
 
-from mmdet.apis import inference_detector, init_detector, show_result
+from mmdet.apis import inference_detector, init_detector
 
 
 def parse_args():
@@ -38,8 +38,8 @@ def main():
         if ch == 27 or ch == ord('q') or ch == ord('Q'):
             break
 
-        show_result(
-            img, result, model.CLASSES, score_thr=args.score_thr, wait_time=1)
+        model.show_result(
+            img, result, score_thr=args.score_thr, wait_time=1, show=True)
 
 
 if __name__ == '__main__':

mmdet/models/detectors/base.py

+import warnings
 from abc import ABCMeta, abstractmethod
 
 import mmcv
@@ -232,4 +233,6 @@ class BaseDetector(nn.Module, metaclass=ABCMeta):
             out_file=out_file)
 
         if not (show or out_file):
+            warnings.warn('show==False and out_file is not specified, only '
+                          'result image will be returned')
             return img