Why does a triangle have 6 vertices?

Newbie & Debugging Questions
#1

I’m drawing learning a bit of LWJGL and I’ve made it up to the point where I draw a triangle with a FloatBuffer. The tutorial sets up the triangle’s vertices like this:


vertices.put(new float[] {
	+0.0f, +0.8f,    // Top Vertex
	+0.8f, -0.8f,    // Bottom-right vertex
	-0.8f, -0.8f     // Bottom-left vertex
});

If IRL math a triangle only has three vertices, why do they have 6 in LWJGL?

#2

An x and a y coordinate…

#3

dont forget z coordinate, i think ;D

#4

Which one would be the X,Y,Z coord? The first number or the second?

#5

You’re drunk Jacob, go home. Don’t know if you’re trolling or what.

If you’re not, each of those pairs are an x and a y coordinate.


{ x1, y1,
  x2, y2,
  x3, y3 }
#6

No z coord as long as its 2D…
It’s xy xy xy.

EDIT: Slyth.

#7

The key to OpenGL is that it doesn’t know what your vertices are part of. You have to tell it.

If you say it’s a triangle with 2-dimensional points, the vertices will be (0, 0.8), (0.8, -0.8), and (-0.8, -0.8).

If you take the same data and say it’s a line with 3-dimensional points, it will be from (0, 0.8, 0.8) to (-0.8, -0.8, -0.8).

Edit: Note to self: Disable smileys when you have an 8 followed by a parenthesis.

#8

Following what Slyth said, visualize it like this:


vertices.put(new float[] {
    (+0.0f, +0.8f), <- 1st with X/Y coords
    (+0.8f, -0.8f), <- 2nd with X/Y coords
    (-0.8f, -0.8f) <- 3rd with X/Y coords
});

You have 3 vertices, so each individual vertex will have its own X and Y coordinates. That’s why you’re passing in 6 values.

  • Jev
#9

Wow, I feel a bit dumb now. Haha I’ve been programming all night perhaps it’s time to take a nap. :stuck_out_tongue: Thanks for letting me know. Haha

#10

goodnight. :wink:

#11

I prefer something to look at, so here’s my basic diagram of this subject.

For starters, here’s an ASCII triangle.
.
/
.___.

Each vertex (which I represented with a period) has x and y values. Since there are 3 vertices in a triangle, there are 6 x and y coordinates. Here’s what the triangle would look like on grid paper:

Make sense?