Beginner Alert - where my quads at?

[dekoffie]

Hello there,

first of all, I'm completly new to openGL, so I'm suspecting the following problem is probably pretty stupid but I just don't seem to find the result.
I followed a lot of tutorials over at NeHe, got them all working just fine and I believe I understand as good as everything that is explained there.
Seeing how I am especialy curious about terrain rendering, I picked up this tutorial here: http://home.planet.nl/~monstrous/terrain.html and started off trying to write my own little "terrain engine": I'm only up to the 2nd algorythm explained on that page, and I'm already stuck;

When I draw my terrain, my display just gives me a black window. Now, I'm thinking it has something to do with perspective and the coordinates system, which I probably don't understand as well I should at the moment. (at least, until now I thought I did )

So here's my code for the initialisation of openGl and the actual rendering method:

/**
	 * Initialise openGL
	 **/
	private void initGL()
	{
	    GL11.glEnable(GL11.GL_TEXTURE_2D); // Enable Texture Mapping
	    GL11.glShadeModel(GL11.GL_SMOOTH); // Enable Smooth Shading
	    GL11.glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // Black Background
	    GL11.glClearDepth(1.0f); // Depth Buffer Setup
	    GL11.glEnable(GL11.GL_DEPTH_TEST); // Enables Depth Testing
        GL11.glDepthFunc(GL11.GL_LEQUAL); // The Type Of Depth Testing To Do
        
        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glLoadIdentity();

        // Calculate The Aspect Ratio Of The Window
        GLU.gluPerspective(
          45.0f,
          (float) Display.getDisplayMode().getWidth() / (float) Display.getDisplayMode().getHeight(),
          0.1f,
          1000.0f);
        GL11.glMatrixMode(GL11.GL_MODELVIEW); 

        GL11.glHint(GL11.GL_PERSPECTIVE_CORRECTION_HINT, GL11.GL_NICEST);
	}

	/**
	 * render()
	 *
	 * render our scene
	 */
	public void render()
	{
        GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
        GL11.glLoadIdentity(); 
		
        GL11.glTranslatef(0.0f, 0.0f, -5.0f);
        GL11.glColor3f(0.0f, 0.5f, 0.1f); // set color
        
		// start rendering
		GL11.glBegin(GL11.GL_QUADS);
		for(float x = 0.0f; x < AREA_SIZE-1; x++)
		{
			for(float z = 0.0f; z < AREA_SIZE-1; z++)
			{
				GL11.glVertex3f(F * (x+1), F * height_map[(int)x+1][(int)z], F*z);
				GL11.glVertex3f(F * x, F * height_map[(int)x][(int)z], F*z);
				GL11.glVertex3f(F * x, F * height_map[(int)x][(int)z+1], F*(z+1));
				GL11.glVertex3f(F * (x+1), F * height_map[(int)x+1][(int)z+1], F*(z+1));
			}
        }
		GL11.glEnd();
	}

The height_map array is filled with this method (as taken from the tutorial above):

/**
	 * generateMap()
	 *
	 * create a random height map
	 */
	private void generateMap()
	{
		float h;
		int x, y;
		
		for(x = 0; x < AREA_SIZE; x++)
		{
			for(y = 0; y < AREA_SIZE; y++)
			{
				h = (float) (10.0 * Math.sin(x/24.0) + 7.0 * Math.cos((y-50.0)/18.0));
				height_map[x][y] = h;
			}
		}
	}

So, could any of you see what I'm doing wrong here?

Thanks in advance for any tips!

[CaseyB]

I take it that your variable F is just a constant multiplier?  What do you have it defined as?

[dekoffie]

I take it that your variable F is just a constant multiplier?  What do you have it defined as?

it's defined as follows:

// world scale of one height map cell
	private final float F = 16.0f;
	// w and h of our map
	private final int AREA_SIZE = 128;

[CaseyB]

I think that the quads you're defining may not be planar.  This is always a concern when using quads instead of triangles.  You may be better off to modify your drawing algorythm and use GL_TRIANGLE_STRIP instead of GL_QUADS.

-=EDIT=-
In fact, I just looked at the tutorial you are linking to and they do just that!

Rendering a grid using triangle strips

[dekoffie]

I think that the quads you're defining may not be planar.  This is always a concern when using quads instead of triangles.  You may be better off to modify your drawing algorythm and use GL_TRIANGLE_STRIP instead of GL_QUADS.

-=EDIT=-
In fact, I just looked at the tutorial you are linking to and they do just that!

Rendering a grid using triangle strips

Thanks for your explanation, and yes I do know that the tutorial was about to do that But still, I'd like to try everything out, to try to make myself sure that I will fully understand all that follows.

So, I hope someone would still be able to know how to fix the above code, if not, well I'll just continue like you said! Thanks a bunch CaseyB!!

[dekoffie]

Well I changed my code to use triangle strips, exact same method as in the tutorial; still I don't get anything on my screen

I am pretty sure the program is doing calculations and drawing it, because sometimes I see some different colors for a split second on the screen (it looks kinda like when you're computer crashes and messes up your entire display and you can't see anything on it) and the mouse cursor changes also.

Any ideas?

[napier]

Have you tried changing your viewpoint?   I don't see a gluLookAt() call in your code, so I'm guessing your viewpoint is at 0,0,0 by default which may not be a good vantage point to actually see the terrain you're generating.

[dekoffie]

Have you tried changing your viewpoint?   I don't see a gluLookAt() call in your code, so I'm guessing your viewpoint is at 0,0,0 by default which may not be a good vantage point to actually see the terrain you're generating.

Thanks a bunch napier! That did the trick!
I can now see my rendered triangle trips, y@y

One question though which I hope you'll be wanting to answer; how exactly does gluLookAt work? I found a good position to look over my terrain, but I only got to it by trying a bunch of different numbers actualy

       GLU.gluLookAt(
        		0.0f, 0.0f, 0.0f, // eye yield (=viewpoint?)
        		(AREA_SIZE / 2), 15.0f, (AREA_SIZE / 2), // center
        		0.0f, 1.0f, 0.0f // upside vector
        );

And now I 'd like to make my camera move throughout the terrain by using the arrows (for starters ); now I did already have some code (learned from NeHe site) but this doesn't use gluLookAt anywhere. I just rotate and translate the scene around the user view. So, does gluLookAt come into play anywhere here?

thanks for the help!

[tomb]

Here is a link to the OpenGL documentation:
http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/

If you look in the glu folder you'll find some information about lookat.

[dekoffie]

Here is a link to the OpenGL documentation:
http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/

If you look in the glu folder you'll find some information about lookat.

Thank you!

[ilazarte]

Great site for a beginner like me.  Thanks.