Cabinet projection trouble

[boxsmith]

Hi guys! I've been working with Slick2D for a while, and my most recent project has finally pushed me to deal more directly with OpenGL. I'm new to all this, so please be nice.

I'm trying to get cabinet projection working, but it's giving me a lot of trouble. I managed to get it to look like cabinet projection like so:

double[] c = {1, 0, 0.05, 0,
	      0, 1, 0.5,  0,
	      0, 0, -1,   0,
	      0, 0, 0,    1};

DoubleBuffer mat = BufferUtils.createDoubleBuffer(16);
mat.put(c).flip();

SlickCallable.enterSafeBlock();
     	     
GL11.glEnable(GL11.GL_BLEND);
GL11.glBlendFunc(GL11.GL_SRC_ALPHA, GL11.GL_ONE_MINUS_SRC_ALPHA);
GL11.glEnable(GL11.GL_DEPTH_TEST);
        		
GL11.glMatrixMode(GL11.GL_PROJECTION);
GL11.glLoadIdentity();
GL13.glLoadTransposeMatrix(mat);
GL11.glOrtho(0, window_size_x, window_size_y, 0, 0, 2048);
		
GL11.glMatrixMode(GL11.GL_MODELVIEW);
GL13.glLoadTransposeMatrix(mat);

...

Then I discovered that the values of zNear and zFar in the glOrtho method seem to play a role in shortening or elongating the scene. How can I prevent them from doing so (that is, how can I ensure that the scene's appearance doesn't change for any value of zNear and zFar)? What exactly do they do? Apparently their purpose is more complicated than I was led to believe.

[boxsmith]

B-b-b-bump.

Help would still very much be appreciated.