Overlaying text or image onto an already-flipped screen

I am using PTB to present static images, and would like to overlay an image with text or a shape after a certain time period. Is it possible to draw onto a texture that has already been flipped? Or can it only be done by creating a new texture with both the old and new stimuli and flipping it again?

Thanks in advance for your help, Katherine

[Image Analyst]

What's "PTB"?

[Katherine]

sorry, PTB=Psychtoolbox

[Image Analyst]

Not sure what that is - it doesn't seem to be a toolbox from the Mathworks. Did you see my answer below?

Answer 1

[T]

I'd recommend asking PTB specific questions on http://tech.groups.yahoo.com/group/psychtoolbox/

You have multiple options.

1. Use Screen('Flip') with the dontClear flag set to 1. The previously drawn stimulus can be overdrawn like that

   [fill in the blanks]

   Screen('DrawTexture')
   Screen('Flip')
   Screen('DrawText')
   Screen('Flip', [], [], 1)

cf. http://docs.psychtoolbox.org/Flip

2. Draw the old texture again, then draw the new thing on top

   Screen('DrawTexture')
   Screen('Flip')
   Screen('DrawTexture')
   Screen('DrawText')
   Screen('Flip')

Normally for graphics applications you redraw everything in every frame. DontClear is a special case.

If you want to draw multiple textures on top of each other you will likely need to set up alpha blending if your textures are supposed to contain irregular, non-rectangle shapes.

[Donna Gift Cabalo]

Hi! I am currently writing a code that present an image and the name(text) of the image at the same time and I used the DrawFormattedText function instead of Screen(DrawText) after DrawTexture. It worked, however, when I tried to replace the text with a predefined array containing the different names of objects (code below), its not working anymore.

DrawFormattedText(mywin, myImagenames, 'center', screenYpixels * 0.25, [1 0 0]);

Do you have any suggestion?

Thanks in advance!

[Aiswarya]

even i have the same issue! please help

Answer 2

[Image Analyst]

I'm not exactly sure what you mean but you could use pause() to wait some specified time then use imshow() to display a new image. I don't know what you mean by "draw onto a texture". Perhaps screenshot(s) would help.

[Katherine]

Thanks. But the stimulus is presented using Screen, and using imshow opens a figure window (separate from the image I've presented). I am presenting visual stimuli to participants so I think I need to use Screen rather than imshow (maybe not though).

To clarify, I have used the following code to present the initial image:

static=imread('C:\feb14\static','bmp');

screen=max(Screen('Screens'));

windowPtr=Screen('OpenWindow',screen,[0 0 0],[100,100,600,600]); texture(1)=Screen('MakeTexture',windowPtr,static); %create texture Screen('DrawTextures',windowPtr,texture(1),[]); %draw texture to screen

Screen('Flip',windowPtr'); %flip to display screen

Is it possible to draw something, e.g., text, on top of this image? I know that it is possible to present two things simultaneously (by drawing both before executing the 'Flip' command), but can text be drawn onto an existing screen window? In essence I want to create a second and transparent layer of the screen.

Hope that is clearer...

[Maria Del Carmen Cortes Molina]

katherine, I am trying to do the same,

did you solve this problem?

Thank you :D

[Image Analyst]

To insert text into the overlay use text.

To burn text into the image, use insertText in the Computer Vision Toolbox.