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Draw a rectangle on an image in gui with mouse hover

Asked by Imran Kanjoo on 11 Jan 2019
Latest activity Commented on by Imran Kanjoo on 14 Jan 2019
This question has two parts.
First I want to draw a rectangle on an image in gui only when the mouse hovers on the image. Secondly, if the user clicks the image execute some statements. Right now, I can only draw the rectangle on the image in following manner,
axes(handles.axes1);
[r,c,~]=size(Image);
rectangle('Position', [-2,-2,c+4,r+4],'EdgeColor','r');

  3 Comments

Imran - do you want to click the mouse button (while the mouse pointer is over the image) and draw the rectangle from that location? What is the relationship between the mouse pointer and the rectangle?
Thank you for reply. I want to draw the rectangle when mouse hovers on the image and when the mouse is out of image then rectangle should get removed. Like mouse on image, draw rectangle on image, mouse not on image no rectangle.
Then when the mouse is on the image and there is a left click on the image then I want to execute some other set of statements. May be you can call it a function
call_when_image_clicked()
I am sorry, I forget to reply second question. These statemens drawing the rectangle on image ver well.
[r,c,~]=size(Image);
rectangle('Position', [-2,-2,c+4,r+4],'EdgeColor','r');
New Bitmap Image.bmp

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1 Answer

Answer by Kevin Phung on 11 Jan 2019
Edited by Kevin Phung on 11 Jan 2019
 Accepted Answer

Hello,
You can use the 'WindowButtonMotionFcn' property of your figure,
f = figure;
set(f,'WindowButtonMotionFcn',@cursorPos)
with the callback function retrieving the position of your cursor:
function cursorPos(my_fig,event)
pos = get(my_fig,'CurrentPoint');
You know the position of your image with:
image_pos = get(image_handle,'Position')
so you can add the logic where if the position is within the bounds of the image: draw a rectangle; else, delete existing rectangle.
If you call the handle of your figure and see all the properties, you can see the various types of callbacks your function can trigger, for example:
WindowButtonDownFcn: ''
WindowButtonMotionFcn: ''
WindowButtonUpFcn: ''
WindowKeyPressFcn: ''
WindowKeyReleaseFcn: ''
WindowScrollWheelFcn: ''
------
The 'WindowButtonDownFcn' should be used for:
set(f,'WindowButtonDownFcn',@call_when_image_clicked)
Hope this helps!

  1 Comment

Hello, Thank you for your reply. I can now WindowButtonMotionFcn and can draw the rectangle. but I am I unable to find the postions of the image. If I find position of the image using
get(eventdata.axes1,'Position')
I get values in points (). and if I use
image_pos = get(eventdata.figure1,'Position')
I get value in even -ve (1084.2 -55.8 2033.6 1115.2). I dont know why negative,
I am using this logic now to draw the rectangle under the WindowButtonMotionFcn.
pos1 = getpixelposition(eventdata.axes1,true)
currentp=src.CurrentPoint
image_pos = get(eventdata.figure1,'Position')
x1=680;
y1=1046;
matlabImage = imread(strcat(num2str(randArr(3)),'.tif'));
[r,c,~]=size(matlabImage);
x2=1397;
y2=512;
if ((currentp(1)<x2&&currentp(1)>x1)&&currentp(2)>y2&&currentp(2)<y1)
% axes(hObject.figure1);
rectangle('Position', [-2,-2,c+4,r+4],'EdgeColor','r','LineWidth',3);
else
rectangle('Position', [-2,-2,c+4,r+4],'EdgeColor',[0,0,0]','LineWidth',3);
end
I need to determine the values of x1,y1,x2,y2.

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