1.shader代码

float Circle(vec2 uv,vec2 center,float r,float blur){
    //相当于uv坐标到中心的距离
    float d = length(uv - center);
    float c = smoothstep(r,r - blur,d);
    return c;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = fragCoord/iResolution.xy;
    //uv -= 0.5;
    //将uv的x坐标进行放大
    uv.x *= iResolution.x / iResolution.y;

    float c = Circle(uv,vec2(1,0.5),0.4,0.05);
    //c>1 按1来处理
    c += Circle(uv,vec2(0.5,0.2),0.1,0.01);
    fragColor = vec4(vec3(c),1.0);
}

2效果:

3.越界问题:
已经做了 ,着色时系统已经处理，返回的颜色的范围在[0,1]之间

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    //大于1按 1处理,纯红
    fragColor = vec4(2,0,0,1.0);
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    //大于1按 1处理,纯黑
    fragColor = vec4(-1,-1,-1,1.0);
}

fixed4 frag (v2f i) : SV_Target
{
    if(i.uv.x <= 0.5){
        //小于0 按0处理 rgb b = 1,蓝色
        return fixed4(-2,-1,3,1);
    }
     //大于1按1处理 白色
    return fixed4(2,2,2,1);
}

效果如下:

mask效果

float Circle(vec2 uv,vec2 center,float r,float blur){
    //相当于uv坐标到中心的距离
    float d = length(uv - center);
    float c = smoothstep(r,r - blur,d);
    return c;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = fragCoord/iResolution.xy;
    //uv -= 0.5;
    //将uv的x坐标进行放大
    uv.x *= iResolution.x / iResolution.y;

    float mask = Circle(uv,vec2(1,0.5),0.4,0.05);
    //c>1 按1来处理
    mask -= Circle(uv,vec2(0.9,0.7),0.1,0.01);
    mask -= Circle(uv,vec2(1.1,0.7),0.1,0.01);
    vec3 col = mask * vec3(1,0,1);
    fragColor = vec4(col,1.0);
}

效果:

表情:

float Circle(vec2 uv,vec2 center,float r,float blur){
    //相当于uv坐标到中心的距离
    float d = length(uv - center);
    float c = smoothstep(r,r - blur,d);
    return c;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = fragCoord/iResolution.xy;
    //uv -= 0.5;
    //将uv的x坐标进行放大
    uv.x *= iResolution.x / iResolution.y;

    float mask = Circle(uv,vec2(1,0.5),0.4,0.05);
    //c>1 按1来处理
    mask -= Circle(uv,vec2(0.9,0.7),0.1,0.01);
    mask -= Circle(uv,vec2(1.1,0.7),0.1,0.01);

    float mouth = Circle(uv,vec2(1,0.4),0.2,0.01);
    mouth -= Circle(uv,vec2(1,0.5),0.2,0.01);

    mask -= mouth;

    vec3 col = vec3(1,1,0) * mask;
    fragColor = vec4(col,1.0);
}

效果:

完整shader:

Shader "Custom/emo"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag


            #include "UnityCG.cginc"

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

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            float Circle(float2 uv,float2 center,float r,float blur){
                //相当于uv坐标到中心的距离
                float d = length(uv - center);
                float c = smoothstep(r,r - blur,d);
                return c;
            }

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                float mask = Circle(i.uv,float2(0.5,0.5),0.4,0.05);
                //c>1 按1来处理
                mask -= Circle(i.uv,float2(0.4,0.7),0.1,0.01);
                mask -= Circle(i.uv,float2(0.6,0.7),0.1,0.01);

                float mouth = Circle(i.uv,float2(0.5,0.4),0.2,0.01);
                mouth -= Circle(i.uv,float2(0.5,0.5),0.2,0.01);

                mask -= mouth;

                fixed3 col = fixed3(1,1,0) * mask;
                fixed4 fragColor = fixed4(col,1.0);
                return fragColor;
            }
            ENDCG
        }
    }
}

效果: