UV序列帧动画

通过上图实现一个火焰的序列帧动画（使用UV实现美术只需要出一张图，而不用每个火焰状态出一张图，节省了内存）。

shader如下：

Shader "Custom/UVAnimation" 
    {
    Properties
    {
        _Color("Base Color", Color) = (1,1,1,1)
        _MainTex("Base(RGB)", 2D) = "white" {}
        _AnimationSpeed("AnimationSpeed", float) = 100 //动画的播放速度
        _FrameCount("FrameCount",float) = 12//这个动画共几帧
    }
    
    SubShader
    {
        tags{"Queue" = "Transparent" "RenderType" = "Transparent" "IgnoreProjector" = "True"}
        Blend SrcAlpha OneMinusSrcAlpha
        
        Pass
        {            
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"
            
            float4 _Color;
            sampler2D _MainTex;
            float _AnimationSpeed;
            float _FrameCount;
            
            struct v2f
            {
                float4 pos:POSITION;
                float2 uv:TEXCOORD0;
            };
            
            //处理动画逻辑
            float2 moveUV(float2 vertUV)
            {                
                float index = frac(_Time.x / _FrameCount * _AnimationSpeed);
                float2 uvScale = float2(1 / _FrameCount, 1);
                
                for(int i = 1; i < _FrameCount + 1; i++)
                {
                    if(index <= uvScale.x * i){
                        return vertUV * uvScale + float2( (i-1) * uvScale.x, 0.0);//计算UV的位移量
                    }
                }

                return vertUV * uvScale + float2((_FrameCount - 1) * uvScale.x, 0.0);
            }
            
            v2f vert(appdata_base v)
            {
                v2f o;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.uv = moveUV(v.texcoord.xy);
                return o;
            }
            
            half4 frag(v2f i):COLOR
            {    
                half4 c = tex2D(_MainTex , i.uv) * _Color;
                return c;
            }            
            ENDCG
        }
    }
}