Using a mouse to draw boxes on the screen

Author: abidrahmank

example_4_1.py

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+''' 
+Referred to example 4-1 in the book "Learning OpenCV: Computer Vision with the OpenCV Library"
+
+Example 4-1. Toy program for using a mouse to draw boxes on the screen
+
+Converted to Python by Abid.K	--mail me at [email protected]
+'''
+########################################################################################
+
+import cv
+#	cvRect	box=[box.x,box.y,box.width,box.height]
+box=[0,0,0,0]
+
+#	creating mouse callback function
+def my_mouse_callback(event,x,y,flags,param):
+	global drawing_box
+	if event==cv.CV_EVENT_LBUTTONDOWN:
+		drawing_box=True
+		[box[0],box[1],box[2],box[3]]=[x,y,0,0]
+		print box[0]
+
+	if event==cv.CV_EVENT_LBUTTONUP:
+		drawing_box=False
+		if box[2]<0:
+			box[0]+=box[2]
+			box[2]*=-1
+		if box[3]<0:
+			box[1]+=box[3]
+			box[3]*=-1
+			
+	if event==cv.CV_EVENT_MOUSEMOVE:
+		if (drawing_box==True):
+			box[2]=x-box[0]
+			box[3]=y-box[1]	
+		
+# 	function to draw the rectangle, added flag -1 to fill rectangle. If you don't want to fill, just delete it.		
+def draw_box(img,box):
+	cv.Rectangle(img,(box[0],box[1]),(box[0]+box[2],box[1]+box[3]),(255,0,0),-1)
+
+#	main program	
+drawing_box=False
+image=cv.CreateImage((200,200),cv.IPL_DEPTH_8U,3)
+#	make a clone of image
+temp=cv.CloneImage(image)
+
+cv.NamedWindow("Box Example")
+cv.SetMouseCallback("Box Example",my_mouse_callback,image)
+while(1):
+	cv.Copy(image,temp)
+	if drawing_box==True:
+		draw_box(temp,box)
+	cv.ShowImage("Box Example",temp)
+	if cv.WaitKey(20)%0x100==27:break
+	
+cv.DestroyWindow("Box Example")
+###################################################################################################