Unity GLSL shader - getting screen coordinates

I am porting a shader toy shader to Unity GLSL. It’s working except I have trouble getting the screen space coordinates I need. What’s the equivalent of this:

vec2 coord = gl_FragCoord.xy / iResolution.xy;

I want the normalised coordinate of the current screen fragment.

It seems gl_FragCoord is not available and how do I get the screen size?

Note that I’m using GLSL as the shader language in Unity not CG or HLSL.

I think I got the answer:

 GLSLPROGRAM // here begins the part in Unity's GLSL

 #include "UnityCG.glslinc"

 vec4 iResolution = _ScreenParams;

Then in main() in fragment shader:

vec2 coord = gl_FragCoord.xy / iResolution.xy;

I must have made a mistake that made me believe I did not have access to gl_FragCoord