glViewport doesnt set the window size

OpenGL Development JOGL Development
#1

Hi

I have only just begun to learn JOGL, i have written several basic programs, but they have all had the same problem. All the drawing works correctly, but when the window is first displayed it is a tiny little square in the top left corner. If the bottom right corner is dragged to expand the window then as I said the drawing is displayed correctly.

Here is the code that i thought was supposed to set the viewable size of the GLCanvas:


public void init(GLAutoDrawable drawable)
{		
	GL lib = drawable.getGL();
	GLU glu = new GLU();
		
	lib.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
	lib.glViewport(-500, -300, 500, 300);  // THIS LINE
	lib.glMatrixMode(GL.GL_PROJECTION);
	lib.glLoadIdentity();
		
	glu.gluOrtho2D(-500.0, 500.0, -300.0, 300.0);
}
#2

Hi,

First it’s quite strange to call the GL object lib… no ???

To change the size of the GLCanvas you have to call setBounds (or setSize) on it. ( Or on the Frame containing it and use a correct layout manager).

The glViewport method is not devoted to that purpose… You should have a look to the jogl samples and the red book to used it properly.
Hope it helps.

#3

I actually got the basis of this code from:

http://www.genedavissoftware.com/books/jogl/ljogl_ch1.html

and as i said, i am new to JOGL, and i figured that the GL object is a single instance used to call library (lib) functions to set state variables… i dunno it made sense to me.

so what exactly is glViewport supposed to do??

#4

I also think it makes sense, but I would call it “context”, since there could be more than one (e.g. using multiple canvases) and the gl object defines the context in which your gl-calls are executed.

It only sets up the math behind converting the opengl-coordinates to pixel coordinates of your canvas: http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/gl/viewport.html

#5

So if you want the window size to be the correct size when it is first opened, you have to set the size of the OpenGL canvas object in the window/frame. In SWT, this is done using GLCanvas.setBounds(). I’m sure JOGL’s GLCanvas has something similar (like a setSize() method).