Child item with an x position greater than its parent panel's width still appears inside it

I get the width of a panel in pixels like this:

set(MyPanel,'units','pixel')
pos = MyPanel.Position;
set(MyPanel,'units','normalized')

The width comes back as 510 px, yet a child of this panel that has an x position of 600 or more still appears inside the panel. How is this possible?

Edit to provide a minimum working example and steps to reproduce the problem:

Step 1: Create an app using the "2-Panel App with Auto-Reflow" template

Step 2: Set startupFcn to the following:

function startupFcn(app)
            drawnow
            fig_position = app.UIFigure.Position;
            fig_width = fig_position(3);
            fig_height = fig_position(4);
            app.GridLayout.ColumnWidth = {0.54*fig_width, 0.46*fig_width};
            app.GridLayout.RowHeight = fig_height;
            
            app.UIFigure.WindowState = 'maximized';
            
            MyPanel = uipanel(app.LeftPanel,"Units","normalized","Position",[0 0.5 1 0.3]);
            
            pos = getpixelposition(MyPanel);
            pos3 = app.LeftPanel.Position;
            pos2 = getpixelposition(app.LeftPanel);
            
end

Step 3: Set a breakpoint at the end of the function and hover over app.LeftPanel.Position and pos3. You will see that the width value for some reason is different! (See images below)

[Bruno Luong]

May be there are some child/objects that you didn't expect it's there, and dind't inspect them?

[John F]

@Bruno Luong No it's a direct child of the Panel. Also, I noticed that the width value returned by MyPanel.Position is incorrect for some reason...

[Bruno Luong]

I can't reproduce what you report:

h=uipanel;
set(h,'unit','pixel');
pp=get(h,'position')

pp = 1×4

1 1 577 433

ax=uiaxes(h);
set(ax,'unit','pixel');
pa=get(ax,'position')

pa = 1×4

10 10 400 300

pa(1)=pp(3)+1

pa = 1×4

578 10 400 300

set(ax,'position',pa) % axes must disappear since it is overflowed on the extrem right side 

[John F]

@Bruno Luong Maybe providing a bit more context will help. I'm building the app using the 2-Panel App with Auto-Reflow template. So the app.LeftPanel has a Position vector of [1 1 864 837]. I define MyPanel as follows:

MyPanel = uipanel(app.LeftPanel,"Units","normalized","Position",[0 0.5 1 0.3])

So in theory the width of MyPanel should be 864 pixels, yet I get 510 pixels (which is the same even if I use the getpixelposition).

[Walter Roberson]

I am unclear as to how the High Density Display accommodations affect these numbers (if at all.)

[John F]

@Walter Roberson The size the app.UIFigure component is in line with my screen resolution, so I assume that it's not an issue. I haven't messed with anything related to High Density Display accommodations either.

[Bruno Luong]

It will be helpful if you can provide a minimum working example.

[John F]

@Bruno Luong I edited the question to provide that.

[Bruno Luong]

With this command

MyPanel = uipanel(app.LeftPanel,"Units","normalized","Position",[0 0.5 1 0.3])

You create another uipanel within the LeftPanel, not the app figure.

As I told above, you might have some other oject that you are not suspected it is there.

[John F]

@Bruno Luong That still doesn't explain what I mention in the edit though.

[Bruno Luong]

I add drawnow (attached test file)

drawnow
MyPanel = uipanel(app.LeftPanel,"Units","normalized","Position",[0 0.5 1 0.3]);
drawnow
pos = getpixelposition(MyPanel);        % <- width 218
pos3 = app.LeftPanel.Position;          % <- width 220
pos2 = getpixelposition(app.LeftPanel); % <- width 220

Command line output without debugger:

>> app1

pos =

1.0000  240.0000  344.0000  143.4000


pos3 =

1     1   346   480


pos2 =

1     1   346   480

>> 

So it reduces 1 pixel each side. Seems like not an abnormal size.

[John F]

@Bruno Luong Yes this is it! For some reason now the width is correct in my app. Thank you!

[Bruno Luong]

Just keep in mind that App and GUI workflow is Event driven, so concurrent and can be quite surprise if you don't pay close attention.