New demo program - demonstrates how to make a "rubber band" rectangle where you click and drag to draw it

DemoPrograms/Demo_Graph_Drag_Rectangle.py

@@ -0,0 +1,53 @@
+import PySimpleGUI as sg
+
+"""
+    Demo - Drag a rectangle to draw it
+
+    This demo shows how to use a Graph Element to (optionally) display an image and then use the
+    mouse to "drag a rectangle".  This is sometimes called a rubber band and is an operation you
+    see in things like editors
+"""
+
+
+# image_file = r'Color-names.png'
+image_file = None       # image is optional
+
+layout = [[sg.Graph(
+            canvas_size=(400, 400),
+            graph_bottom_left=(0, 400),
+            graph_top_right=(400, 0),
+            key="-GRAPH-",
+            change_submits=True,  # mouse click events
+            drag_submits=True),],
+            [sg.Text("", key="info", size=(60, 1))]]
+
+window = sg.Window("draw rect on image", layout, finalize=True)
+# get the graph element for ease of use later
+graph = window["-GRAPH-"]     # type: sg.Graph
+
+graph.DrawImage(image_file, location=(0,0)) if image_file else None
+dragging = False
+start_point = end_point = prior_rect = None
+
+while True:
+    event, values = window.Read()
+    if event is None:
+        break  # exit
+    if event == "-GRAPH-":                      # if there's a "Graph" event, then it's a mouse
+        x, y = values["-GRAPH-"]
+        if not dragging:
+            start_point = (x, y)
+            dragging = True
+        else:
+            end_point = (x, y)
+        if prior_rect:
+            graph.DeleteFigure(prior_rect)
+        if None not in (start_point, end_point):
+            prior_rect = graph.DrawRectangle(start_point, end_point, line_color='red')
+    elif event.endswith('+UP'):                 # The drawing has ended because mouse up
+        info = window.Element("info")
+        info.Update(value=f"grabbed rectangle from {start_point} to {end_point}")
+        start_point, end_point = None, None     # enable grabbing a new rect
+        dragging = False
+    else:
+        print("unhandled event", event, values)