why need c_scr?

[Wu-Xiuchao]

Hi~
I am reading the shader code now. And I have already been clear about most of them.
However , in attribure_vs.glsl, I am confused about c_scr, which is computed as follows:

Out.c_scr = vec2((p_scr.xy + 1.0) * viewport.zw * 0.5);

I know p_scr is the point c in screen space, so what does c_scr mean? And what is the difference between them?

[Wu-Xiuchao]

OK， I think I have figured it out.
Because p_scr is in the range [-1,1], and c_scr use pixel unit.