【Unity】ジオメトリーシェーダーでポリゴンをバラバラにする【Shader】

Polygonoperator.shader

Shader "Unlit/Polygonoperator"
{
	Properties
	{
	_MainTex ("Texture", 2D) = "white" {}
        _MainColor("Color",Color)=(1,1,1,1)
        _PositionFactor("Position Factor", Range(0.0, 1.0)) = 1.0
        _RotationFactor("Rotation Factor", Range(0.0, 1.0)) = 1.0
        _ScaleFactor("Scale Factor", Range(0.0, 1.0)) = 1.0  
        _Destruction("Destruction Factor", Range(0.0, 1.0)) = 0.0
	}
    
	SubShader
	{
	Tags 
        { 
            "RenderType" = "Transparent"
            "Queue" = "Transparent" 
        }
	LOD 100
        Blend SrcAlpha OneMinusSrcAlpha
        
	Pass
	{
		CGPROGRAM
		#pragma vertex vert
		#pragma geometry geom
            	#pragma fragment frag
			
		#include "UnityCG.cginc"

		struct appdata
		{
			float4 vertex : POSITION;
			float2 uv : TEXCOORD0;
		};

		struct g2f
		{
			float2 uv : TEXCOORD0;				
			float4 vertex : SV_POSITION;
		};
            
            	float rand(fixed2 seed){
                	return frac(sin(dot(seed.xy ,fixed2(12.9898,78.233))) * 43758.5453);
            	}
            
            	fixed3 rotate(fixed3 p, fixed3 rotation)
            	{
                	fixed3 a = normalize(rotation);
                	fixed angle = length(rotation);
                	if (abs(angle) < 0.001) return p;
                	fixed s = sin(angle);
                	fixed c = cos(angle);
                	fixed r = 1.0 - c;
                	fixed3x3 m = fixed3x3(
                    		a.x * a.x * r + c,
                    		a.y * a.x * r + a.z * s,
                    		a.z * a.x * r - a.y * s,
                    		a.x * a.y * r - a.z * s,
                    		a.y * a.y * r + c,
                    		a.z * a.y * r + a.x * s,
                    		a.x * a.z * r + a.y * s,
                    		a.y * a.z * r - a.x * s,
                    		a.z * a.z * r + c
                	);
                	return mul(m, p);
            	}
            
            	sampler2D _MainTex;
            	fixed4 _MainColor;
            	fixed _PositionFactor;
            	fixed _RotationFactor;
            	fixed _ScaleFactor;
            	fixed _Destruction;
            				
		appdata vert (appdata v)
		{
			return v;
		}
			
            	[maxvertexcount(3)]
            	void geom(triangle appdata input[3], inout TriangleStream<g2f> outStream)
            	{
                	//ポリゴンの中心を計算。
                	float3 center = (input[0].vertex + input[1].vertex + input[2].vertex).xyz / 3;
                
                	//法線計算
                	float3 vec1 = input[1].vertex - input[0].vertex;
                	float3 vec2 = input[2].vertex - input[0].vertex;
                	float3 normal = normalize(cross(vec1, vec2));
                
                	fixed r = 2.0 * (rand(center.xy) - 0.5);
                	fixed3 r3 = r.xxx;
                
                	[unroll]
                	for(int i=0;i<3;i++)
                	{
                    		appdata v=input[i];
                    		g2f o;
                    
                    		//scale
                    		v.vertex.xyz = (v.vertex.xyz - center) * (1-_Destruction * _ScaleFactor) + center;
                    		//rotation
                    		v.vertex.xyz = rotate(v.vertex.xyz - center, r3 * _Destruction * _RotationFactor) + center;
                    		//position
                    		v.vertex.xyz += normal * _Destruction * _PositionFactor * r3;
                    
                    		o.vertex=UnityObjectToClipPos(v.vertex);
                                        
                    		o.uv=v.uv;
                    		outStream.Append(o);
                	}

                	outStream.RestartStrip();
            	}
            
		fixed4 frag (g2f i) : SV_Target
		{				
			fixed4 col=tex2D(_MainTex, i.uv)*_MainColor;          
                	return col;
		}
		ENDCG
		}
	}
}