Fix retina rendering on OSX
This does not actually improve any graphics, but at least OSX native
GUI elements won't look pixellated any more.
attribute vec2 vertex;
attribute vec4 color;
varying vec4 vcolor;
uniform mat4 mvp;
void main()
{
vec4 p = mvp * vec4(vertex, 0.0, 1.0);
gl_Position = p;
vcolor = color;
}