Get the left-most quad appear to the right when dissappearing to the left

OpenGL Development JOGL Development
#1

Hello!

The method called from the display list draws some quads in a horizontal line. You can make the quads going left or right by pressing the arrow keys, then the X_POS variable is changing. When you press left or right many times, the quads will finally disappear from the view.

gl.glTranslatef(X_POS, 0.0f, -6.0f);
gl.glCallList(quad);

I would like to make the left-most quad appear on the right side when it dissappears to the left, and the right-most quad appear to the left when it dissappears to the right, so that the quads never disappear from the view even if I press the left left key for a month. :slight_smile:

How can I achieve this?

#2

Basically you’re interested in the range on the x-axis that is valid.

if x is left of this range, remove the quad from the left, add it to the right
if x is right of this range, remove the quad from the right, add it to the left

add some margin, so that [the quad that just went out of view on one side, gets relocated, and is out of view on the other side], it not moved around again.

For samplecode in javascript (… I know …) look at the sourcecode:
http://www.kewloxfotokasten.nl/
It renders those 4 images at the bottom in this infinite ‘slider’.

#3

Ok, now I am moving all the quads with glTranslatef(), that means every quad is moving. Do I have to use one glTranslatef() for each quad?

#4

Yes, since they all will have independent translations.

#5

No need. You know that the space between the quads is constant, so you can use 1 glTranslate call, you just have to be very sure which value you pass, and what vertex data you pass to the GPU.

#6

My goal is to make the space between the quads constant. The only place where it is not constant is between the left-most and the right-most quads. And that is what I am wondering of how to do. I cannot see how I can solve it with only one glTransate (well, I still don´t see how I can solve it with multiple glTranslates either)?