How to achieve identical timing of two side by side annotations

I have a figure that is just a full-screen white box. On this figure, I want to draw a green cross in the center, and a colored rectangle at the same height but at the left edge of the screen. It's very important that these two annotations appear at the exact same time for a research project.

This is what I am currently doing, but I don't really know for sure how it works and am worried that the cross annotation might be drawn before the rectangle is drawn:

annotation('textbox',[0,0,1,1],'String','+',...
                'FontName','Arial','FontSize',108,...
                'Color',cross_color,...
                'EdgeColor','none',...
                'HorizontalAlignment','center','VerticalAlignment','middle');
            
annotation('rectangle',[0,0.45,0.05625,0.1],'Color','k','FaceColor','k');
 
drawnow;

Answer 1

[Fangjun Jiang]

What you can do is this. I think it can improve the timing.

h1=annotation(..., 'visible','off'):

h2=annotation(..., 'visible','off');

set([h1,h2],'visible','on')

[Walter Roberson]

In theory multiple graphics calls are not dispatched to the render thread until drawnow() or pause() or uiwait() or waitfor() or figure() or you get back to the keyboard, so if you build two objects in succession before doing drawnow() then they should render at the same time.

... In theory.

In practice, if the queued changes can affect multiple axes, requiring that positions be recalculated, it is not certain that the rendering will happen at the same time. For example putting in an axes label can require that the drawing area be reduced in order to fit the text, and that can affect xlim / ylim, and that can affect sizes or clipping...

[Kara Presbrey]

Is the code above a case where multiple axes are affected?

[Walter Roberson]

Tricky. Annotations are not made to the current axes. Annotations are drawn into a pane that is logically "in front" of all other items, using figure coordinates (not data coordinates!). The first annotation() for the figure could potentially involve creation of an annotation pane.

Hmmm... looks like perhaps these days annotations are potentially in uipanel() or uitab() rather than in figures directly, so there could be multiple such objects per figure, so it would make even more sense for the first annotation() call in the container to need to build the annotation pane.

Which suggests that potentially if you did

h0 = annotation(something, 'visible', 'off');  %force annotation pane to be built
drawnow()
%now draw the two useful annotations. In theory should not need 'visible',
%'off' for this.

then you just might get more consistent timing.

Answer 2

[Walter Roberson]

For anything like this you should probably be using the third party Psychtoolbox http://psychtoolbox.org/

[Kara Presbrey]

indeed. Unfortunately, the entire task is coded not with psychtoolbox already

[Walter Roberson]

Could you use Computer Vision Toolbox insertText() and insertShape() to draw into an array, then image() the array so that everything becomes visible at the same time?