custom clipping shader on top of standard shader? (unity) - unity3d

Question

I want to draw a horizontal line on an object with shader code (hlsl).
The clipping shader simply takes the distance to a given Y-coordinate in the surface shader and checks if it is higher that a given value.
If so it will discard. The result is a shader that simply clips away all pixels that are not on a line.
void surf (Input IN, inout SurfaceOutputStandard o) {
// Albedo comes from a texture tinted by color
fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
float d = abs(_YClip - IN.worldPos.y); // _YClip is is the properties and can be changed
if (d > _LineThickness) {
discard;
}
}
Can I somehow combine this shader with the standard unity shader without changing the code?
I plan to have a gizmo shader that renders lines and all kind of stuff. It would be very practical if I could just tell unity to render this gizmo shader on top.

Answer 1

I believe you might be able to use or adapt this shader to your purpose.
Image showing before y axis reached.
Image showing during, where one half is above cutoff y value and other half is below. Note that the pattern it dissolves in, depends on a texture pattern you supply yourself. So it should be possible to have a strict cutoff instead of a more odd and uneven pattern.
After the object has fully passed by the cutoff y value. What I did in this case is to hide an object inside the start object that is slightly smaller than the first object you saw. But if you don't have anything inside, the object will just be invisible, or clipped.
Shader "Dissolve/Dissolve"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
_DissolveTexture("Dissolve Texture", 2D) = "white" {}
_DissolveY("Current Y of the dissolve effect", Float) = 0
_DissolveSize("Size of the effect", Float) = 2
_StartingY("Starting point of the effect", Float) = -1 //the number is supposedly in meters. Is compared to the Y coordinate in world space I believe.
}
SubShader
{
Tags { "RenderType"="Opaque" }
LOD 100
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
// make fog work
//#pragma multi_compile_fog
#include "UnityCG.cginc"
struct appdata
{
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
};
struct v2f
{
float2 uv : TEXCOORD0;
//UNITY_FOG_COORDS(1)
float4 vertex : SV_POSITION;
float3 worldPos : TEXCOORD1;
};
sampler2D _MainTex;
float4 _MainTex_ST;
sampler2D _DissolveTexture;
float _DissolveY;
float _DissolveSize;
float _StartingY;
v2f vert (appdata v) //"The vertex shader"
{
v2f o;
o.vertex = UnityObjectToClipPos(v.vertex);
o.uv = TRANSFORM_TEX(v.uv, _MainTex);
o.worldPos = mul(unity_ObjectToWorld, v.vertex).xyz;
//UNITY_TRANSFER_FOG(o,o.vertex);
return o;
}
fixed4 frag (v2f i) : SV_Target //"For drawing the pixel on top"
{
float transition = _DissolveY - i.worldPos.y; //Cutoff value where world position is taken into account.
clip(_StartingY + (transition + (tex2D(_DissolveTexture, i.uv)) * _DissolveSize)); //Clip = cutoff if above 0.
//My understanding: If StartingY for dissolve effect + transition value and uv mapping of the texture is taken into account, clip off using the _DissolveSize.
//This happens to each individual pixel.
// sample the texture
fixed4 col = tex2D(_MainTex, i.uv);
// apply fog
//UNITY_APPLY_FOG(i.fogCoord, col);
//clip(1 - i.vertex.x % 10); //"A pixel is NOT rendered if clip is below 0."
return col;
}
ENDCG
}
}
}
Here you see the inspector fields available.
I have a similar script with the x axis.