[Unity] GPU动画实现（五）——渲染GPU动画_unity_vertex_input_instance_id

GPU动画实现的最后一步是在shader中重新进行顶点采样。

将动画数据存在一张图片上，每帧动画数据就是一行，因此每个顶点的位置由2个属性确定

1.帧数

2.顶点ID

帧数 = 当前时间 / 动画时间

顶点ID则通过UNITY_VERTEX_INPUT_INSTANCE_ID，Unity会自动将该顶点ID传入

因此，在shade中，进行如下定义，这里直接用最简单的unlit shader示例

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                uint vid : SV_VERTEXID;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };
 
            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

在顶点着色器中，直接进行顶点位置修改，通过顶点ID和动画时间计算取得顶点的位置。

            v2f vert (appdata v)
            {
                v2f o;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_TRANSFER_INSTANCE_ID(v, o);
				float4 uv_anim = float4((v.vid + 0.5) * UNITY_ACCESS_INSTANCED_PROP(Props, _AnimTex_TexelSize).x, _Time.y / UNITY_ACCESS_INSTANCED_PROP(Props, _AnimTime),0.0,0.0);
				v.vertex = float4(tex2Dlod(_AnimTex, uv_anim).xyz,1.0);
                //v.vertex.y = v.vertex.y - 0.5;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv * UNITY_ACCESS_INSTANCED_PROP(Props, _MainTex_ST).xy + UNITY_ACCESS_INSTANCED_PROP(Props, _MainTex_ST).zw;
                return o;
            }

片元着色器不用特别处理，直接采样输出即可

着色器源码如下

 
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _AnimTex ("Texture", 2D) = "white" {}
        _AnimTime ("AnimTime", float) = 1
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100
 
        Pass
        {
            CGPROGRAM
            #pragma target 3.5
            #pragma vertex vert
            #pragma fragment frag
            // make fog work
            #pragma multi_compile_instancing
 
            #include "UnityCG.cginc"
 
            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                uint vid : SV_VERTEXID;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };
 
            struct v2f
            {
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
                float4 vertex : SV_POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };
 
            CBUFFER_START(UnityPerMaterial)
            sampler2D _MainTex;
            sampler2D _AnimTex;
            //float4 _MainTex_ST;
            
			UNITY_INSTANCING_BUFFER_START(Props)
				UNITY_DEFINE_INSTANCED_PROP(float4, _AnimTex_TexelSize)
				UNITY_DEFINE_INSTANCED_PROP(float4, _MainTex_ST)
				UNITY_DEFINE_INSTANCED_PROP(float, _AnimTime)
			UNITY_INSTANCING_BUFFER_END(Props)
            CBUFFER_END
             
            v2f vert (appdata v)
            {
                v2f o;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_TRANSFER_INSTANCE_ID(v, o);
				float4 uv_anim = float4((v.vid + 0.5) * UNITY_ACCESS_INSTANCED_PROP(Props, _AnimTex_TexelSize).x, _Time.y / UNITY_ACCESS_INSTANCED_PROP(Props, _AnimTime),0.0,0.0);
				v.vertex = float4(tex2Dlod(_AnimTex, uv_anim).xyz,1.0);
                //v.vertex.y = v.vertex.y - 0.5;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv * UNITY_ACCESS_INSTANCED_PROP(Props, _MainTex_ST).xy + UNITY_ACCESS_INSTANCED_PROP(Props, _MainTex_ST).zw;
                return o;
            }
 
            fixed4 frag (v2f i) : SV_Target
            {
                UNITY_SETUP_INSTANCE_ID(i);
                fixed4 col = tex2D(_MainTex, i.uv);
                //return float4(1.0,1.0,1.0,1.0) * _Time.y;
                return col;
            }
            ENDCG
        }
    }