Merge pull request #1802 from PySimpleGUI/Dev-latest

New Demo Program that shows how to use an Graph Element to display  O…

DemoPrograms/Demo_OpenCV_Draw_On_Webcam_Image.py

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+import PySimpleGUI as sg
+import cv2
+
+"""
+    Demonstration of how to use a GRAPH ELEMENT to draw a webcam stream using OpenCV and PySimpleGUI.
+    Additionally, the thing this demo is really showcasing, is the ability to draw over the top of this
+    webcam stream, as it's being displayed.  To "Draw" simply move your mouse over the image, left click and hold, and
+    then drag your mouse.  You'll see a series of red circles on top of your image.
+    CURRENTLY ONLY WORKS WITH PySimpleGUI, NOT any of the other ports at this time.
+"""
+
+def main():
+    layout = [[sg.Graph((600,450),(0,450), (600,0), key='_GRAPH_', enable_events=True, drag_submits=True)],]
+
+    window = sg.Window('Demo Application - OpenCV Integration', layout)
+
+    graph_elem = window.Element('_GRAPH_')      # type: sg.Graph
+
+    id = None
+    # ---===--- Event LOOP Read and display frames, operate the GUI --- #
+    cap = cv2.VideoCapture(0)
+    while True:
+        event, values = window.Read(timeout=0)
+        if event in ('Exit', None):
+            break
+
+        ret, frame = cap.read()
+        imgbytes=cv2.imencode('.png', frame)[1].tobytes()
+        if id:
+            graph_elem.DeleteFigure(id)             # delete previous image
+        id = graph_elem.DrawImage(data=imgbytes, location=(0,0))    # draw new image
+        graph_elem.TKCanvas.tag_lower(id)           # move image to the "bottom" of all other drawings
+
+        if event == '_GRAPH_':
+            graph_elem.DrawCircle(values['_GRAPH_'], 5, fill_color='red', line_color='red')
+    window.Close()
+
+main()