GL11.glPushAttrib(GL11.GL_ALL_ATTRIB_BITS);
	GL11.glPushMatrix();

	GL11.glColor4f((float)RGB[0]/255, (float)RGB[1]/255, (float)RGB[2]/255, .6f);
                int top = BAR_SPACING + (iteration * (BAR_SPACING + BAR_HEIGHT));
	int left = BAR_SPACING;
	GL11.glBegin(GL11.GL_LINE_LOOP);
	{
		GL11.glVertex2i(left, top);
		GL11.glVertex2i(left + BAR_WIDTH, top);
		GL11.glVertex2i(left + BAR_WIDTH, top + BAR_HEIGHT);
		GL11.glVertex2i(left, top + BAR_HEIGHT);
	}
	GL11.glEnd();

	GL11.glColor4f((float)RGB[0]/255, (float)RGB[1]/255, (float)RGB[2]/255, .8f);
	GL11.glBegin(GL11.GL_QUADS);
	{
		int right = left + (int)(new Float(BAR_WIDTH) / percent);
		GL11.glVertex2i(left, top);
		GL11.glVertex2i(right, top);
		GL11.glVertex2i(right, top + BAR_HEIGHT);
		GL11.glVertex2i(left, top + BAR_HEIGHT);			
	}
	GL11.glEnd();
                GL11.glPopMatrix();
	GL11.glPopAttrib();

I am trying to draw an open rectangle and then fill in a percent of it.

As is this code draws the rectangle but doesn't fill it.

 

If I switch around the vertices in the second part to this:

                        GL11.glVertex2i(left, top);
		GL11.glVertex2i(right, top);
		GL11.glVertex2i(left, top + BAR_HEIGHT);
		GL11.glVertex2i(right, top + BAR_HEIGHT);

I fills in a triangle using the right side and the bottom left corner.

 

Any idea what I need to do to get it to fill a rectangle?

Arent QUADS (front face) drawn anti-clockwise (unless you make double-sided face)? I think it should solve problem.

 

Also: Why not use tesselator (WorldRenderer)?

Have a look at Gui.class - it shows basic usage of this thingy.

I personally really like that format (it allows a lot of vertex options).

 

I personally wrote it similar but to be static, accept doubles and use RGBA.

Some of Gui.class methods use ARGB i think (and some just RBG for sure).