glReadPixels, glDrawPixels / Overlay crash

OpenGL Development JOGL Development
#1

Good morning :slight_smile:

I try to create a zoom function that magnifies the content of the screensection where the mouse is being dragged over and draws it in a corner.

Since I am fairly new in the Jogl world, I tried to do sth basic. I get the content with

			gl.glReadPixels(0, 0, this.width, this.height, GL.GL_BGRA, GL.GL_UNSIGNED_BYTE, buffer );

(where width/height are the current width and height of the canvas) and buffer is the ByteBuffer).

Then I draw the buffer content with

			gl.glWindowPos2i(0,0);
			gl.glPixelZoom(0.25f, 0.25f);
			gl.glDrawPixels(this.width, this.height, GL.GL_BGRA, GL.GL_UNSIGNED_BYTE, buffer);

Okay, no problem until now and I have got a small screen which shows me the content of the canvas 1:1.

But here is my problem: The GLCanvas is embedded on a JFrame with a Menu/Toolbar.
The toolbar is dragable. When I place it over the Canvas I get a

 java.lang.IndexOutOfBoundsException

So from what I have read, glReadPixels can only be called on a Canvas that is in the front.

What different approach can I use to reach the same result?

Take care
randy

#2

If you are using Swing you should really use GLJPanel.

#3

Hi zingbat,

thank you for your input. I tried it with GLJPanel aswell, but it still gives me that Exception :’(
The reason I was using GLCanvas in the first place was because it gave me 10+fps more than a GLJPanel.

Could you please explain to me why a GLJPanel is better in my Swing Application?

#4

Check this thread. Maybe it helps.
http://java.sun.com/products/jfc/tsc/articles/mixing/

#5

What is throwing the exception?

#6

What is the full stack-trace? JOGL would not be throwing an exception of that type if it’s because of glReadPixels. Then it’d be a GLException, or the JVM would crash.

It’s more likely the case that your code that drags the menu, or sets up your frames is the cause.

#7

Check the variable values on drag or post the trace bcuz as lhkbob said its mostly a problem in the code not regarding OpenGL calls