Why not vec3 for OpenGL ES 2.0 gl_Position?

opengl-es-2.0 shader

peter · Mar 30, 2012 · Viewed 12.7k times · Source

I am new to OpenGL ES 2.0, and cannot understand the following simplest shader:

attribute vec4 vPosition;
void main()
{
   gl_Position = vPosition;
}

My question is, since a position would be a vector of (x, y, z), why is gl_Position a vec4 instead of vec3?

Answer

The w in vec4(x, y, z, w) is used for clipping, and plays its part while linear algebra transformations are applied to the position.

By default, this should be set to 1.0.