what is _ProjectionParams and _ScreenParams?

Unity Engine
1 
inline float4 ComputeScreenPos (float4 pos) {

  float4 o = pos * 0.5f;

  #if defined(UNITY_HALF_TEXEL_OFFSET)

  o.xy = float2(o.x, o.y*_ProjectionParams.x) + o.w * _ScreenParams.zw;

  #else

  o.xy = float2(o.x, o.y*_ProjectionParams.x) + o.w;

  #endif

I read the function “ComputeScreenPos” in UnityCG.cginc. well I search all the document but cant find any explain about _ProjectionParams and _ScreenParams. what i

2

http://docs.unity3d.com/Manual/SL-BuiltinValues.html

Down the bottom :wink:

3

According to Unity Shader Variable in the manual. It is:

Name | Type | Value
_ProjectionParams | float4 | x is 1.0 (or –1.0 if currently rendering with a flipped projection matrix), y is the camera’s near plane, z is the camera’s far plane and w is 1/FarPlane.