Can't get a simple Vertex Array to work!

Newbie & Debugging Questions
#1

So I have a very simple renderer that uses a display list. I am trying to convert it to use a VBO. The step before a VBO is doing a vertex array (upload every frame). I can not get that to work. I’ve been trying everything I can think of for like an hour and got nowhere.

Here’s the old displaylist code:


public final class RenderReticle<Void> extends Renderer<Void> {
	public static final RenderReticle INSTANCE = new RenderReticle();
	
	private static final float size = 25f;
	private static final float halfSize = size / 2;
	
	private DisplayList displayList;
	private Texture texture;
	
	private RenderReticle() {
		
	}
	
	@Override
	public void init() {
		this.displayList = new DisplayList();
		this.displayList.startDrawing();
		
		glBegin(GL_QUADS);
		glTexCoord2f(0f, 0f); glVertex2f(0.0f, 0.0f);
		glTexCoord2f(0f, 1f); glVertex2f(0.0f, size);
		glTexCoord2f(1f, 1f); glVertex2f(size, size);
		glTexCoord2f(1f, 0f); glVertex2f(size, 0.0f);
		glEnd();

		this.displayList.stopDrawing();
		
		this.texture = Texture.get("reticle");
	}
	
	@Override 
	public void render(final Void object) {
		gluSet2D();
		
		glTranslatef(Window.instance().getWidth() / 2 - halfSize, Window.instance().getHeight() / 2 - halfSize, 0);
		
		this.texture.bind();
		this.displayList.call();
		
		gluSet3D();
	} 
}

And here’s the new vertex array code:


public final class RenderReticle<Void> extends Renderer<Void> {
	public static final RenderReticle INSTANCE = new RenderReticle();
	
	private static final float size = 1f;
	private static final float halfSize = size / 2;
	
	private Texture texture;
	
	private FloatBuffer vBuffer;
	private FloatBuffer tBuffer;

	private RenderReticle() {
		
	}
	
	@Override
	public void init() {
		this.vBuffer = BufferUtils.createFloatBuffer(8);
		this.vBuffer.put(0).put(0);
		this.vBuffer.put(0).put(size);
		this.vBuffer.put(size).put(size);
		this.vBuffer.put(size).put(0);
		this.vBuffer.flip();
		
		this.tBuffer = BufferUtils.createFloatBuffer(8);
		this.tBuffer.put(0).put(0);
		this.tBuffer.put(0).put(1);
		this.tBuffer.put(1).put(1);
		this.tBuffer.put(1).put(0);
		this.tBuffer.flip();
		
		this.texture = Texture.get("reticle");
	}
	
	@Override 
	public void render(final Void object) {
		gluSet2D();
		
		glTranslatef(Window.instance().getWidth() / 2 - halfSize, Window.instance().getHeight() / 2 - halfSize, 0);
		
		this.texture.bind();

		glEnableClientState(GL_VERTEX_ARRAY);
		glEnableClientState(GL_TEXTURE_COORD_ARRAY);
	
		glVertexPointer(4, GL_FLOAT, 2 << 2, this.vBuffer);
		glTexCoordPointer(4, GL_FLOAT, 2 << 2, this.tBuffer);
		glDrawArrays(GL_QUADS, 0, 4);
		
		glDisableClientState(GL_VERTEX_ARRAY);
		glDisableClientState(GL_TEXTURE_COORD_ARRAY);
		
		gluSet3D();
	} 
}

“gluSet2D” and “gluSet3D” are functions I wrote. They basically just do glOrtho and the perspective matrix respectively.

So, how come the first one works but the second one doesn’t? (It just displays nothing on the screen).

#2

You are doing everything right, except that your vertex has only 2 components, not 4. So use a 2 as the first argument to glVertexPointer and glTexCoordPointer.

EDIT: Btw.: this is not an error, but specifying the stride (third argument to glVertexPointer/glTexCoordPointer) with “2<<2” (which produces the correct result 8 ) is a bit non-intuitive. You could use “4 * 2” or “2 * 4” meaning (2 floats, each taking 4 bytes). That would be a bit better to read/understand.
But since you are not using interleaved vertex arrays, you can just as well leave that third parameter 0.

#3

Oh, I thought the first parameter was the number of vertices. Doh.

EDIT: nevermind it works, I’m just dumb.

#4

@KaiHH: I prefer <<2 over *4, as it immediately shows we are bitshifting from ints/floats to bytes, whereas *4 can have any meaning (are we working with an attribute with 4 elements?). IMHO it helps to create this convention of using bit shifts to go from one primitive width to another.