If you want the canvas to take up the whole screen, you can edit the WindowState of the UIFigure in AppDesigner with the Component Browser found on the right panel as shown below.
Another approach, is to use a startup function. On the Editor tab in code view, select Callback. Select the app and then select StartFcn for Callback.
In the startup function, you can convert the units of the uifigure to normalized units and the adjust the position then convert back to pixels units.
function startupFcn(app)
app.UIFigure.Units = "normalized";
app.UIFigure.Position(1) = 0.3;
app.UIFigure.Position(2) = 0.3;
app.UIFigure.Units = "pixels";
end
If you want to take into consideration the different resolution ratio bewteen the x and y axes, you can get the entire screensize as shown below and make adjustments to maintain a particular rectangular shape.
function startupFcn(app)
screen = get(0,'screensize');
xres = screen(3)-screen(1);
yres = screen(4)-screen(2);
app.UIFigure.Units = 'normalized';
app.UIFigure.Position = [0.06, 0.60, 0.3*(yres/xres),0.3];
app.UIFigure.Units = "pixels";
end
