See-through hole via shaders on a 2D plane

Questions & Answers
1

Hi!

I need to make a see through hole on a 2D texture using a custom shader.
Defined variables are:
r (hole radius)
x,y (hole position, either by float or vector2)
slope (not necessary, but a useful feature to set a alpha slope for our hole)

The way it should work is when a user wants to see through a building in a 2D game, he simply moves his mouse above it and then we change input variables via simple script command (renderer.material.SetFloat( “_Radius”, radius);, etc) we make that texture see-through, like the example below:

alt text

The building and grass are two separate orth 2d textures.

Is there a way of doing it without using Alpha test or anything expensive like that? (iOS project)

Thanks a lot guys

2

Whether it’s expensive depends on how many pixels you’re blending. You haven’t specified what orientation your world is in, so the properties here are in UV space. You could do it in world space, in 3D, as a generic solution, but I think it might be faster to only deal with two dimensions.

Shader "Hole Thing" {

Properties {
    _Center ("Hole Center", Vector) = (.5, .5, 0 , 0)
    _Radius ("Hole Radius", Float) = .25
    _Shape ("Hole Shape", Float) = .25
    _MainTex ("Main Texture", 2D) = ""
}

SubShader {
	Tags {"Queue" = "Transparent"}
	Blend SrcAlpha OneMinusSrcAlpha
	Pass {
		CGPROGRAM
		struct appdata {
		    float4 position : POSITION;
		    half2 texCoord : TEXCOORD;
		}; 
		
		struct v2f {
			float4 position_clip : SV_POSITION;
			half2 position_uv : TEXCOORD;
		};
		
		#pragma vertex vert
		uniform half4 _MainTex_ST;
		v2f vert(appdata i) {
			v2f o;
			o.position_clip = mul(UNITY_MATRIX_MVP, i.position);
			o.position_uv = _MainTex_ST.xy * i.texCoord + _MainTex_ST.zw;
			return o;
		}
		
		#pragma fragment frag
		uniform sampler2D _MainTex;
		uniform half2 _Center;
		half _Radius, _Shape;
		fixed4 frag(v2f i) : COLOR {		
			fixed4 fragColor = tex2D(_MainTex, i.position_uv);
			half hole = min(distance(i.position_uv, _Center) / _Radius, 1.);
			fragColor.a *= pow(hole, _Shape);
			return fragColor;
		}
		ENDCG
	}
}

}
3

@Jessy’s got a good shader there, just thought I’d pitch a different option.

Why not just render a cylinder with the DepthMask shader though - that would do it if you could live without the edge fading and is very easy to position at the mouse point, especially if overlapping two different textures.