How do you write an unlit shader which supports Ambient Occlusion?

Question

For performance reasons, a scene might use Unlit shaders only.
Is there an Unlit shader which supports Ambient Occlusion?
What is the best way to achieve this look, for moving and static objects, while prioritising performance?

Answer 1

One approach is to create AO maps in 3d modelling software (example in blender) and use that in your shader.

Shader "Unlit/UnlitColorAO"
{
    Properties
    {
        _Color ("Main Color", Color) = (1,1,1,1)
        //_MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}

        _AOTexture ("AO Texture", 2D) = "white" {}
        _AOColor ("AO Color", Color) = (1, 1, 1, 1)
        _AOPower ("AO Texture Power", Range(0, 3)) = 0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            uniform sampler2D _AOTexture;
            uniform fixed4 _AOTexture_ST;
            uniform half3 _AOColor;
            uniform half _AOPower;

            fixed4 _Color;

            static const half3 whiteColor = half3(1, 1, 1);

            struct appdata
            {
                float4 vertex : POSITION;
                half3 normal : NORMAL;
                half3 vColor : COLOR;
                float4 uv0 : TEXCOORD0;
                //float4 uv1 : TEXCOORD1;
            };

            struct v2f
            {
                float4 pos : POSITION;
                //float4 worldPos : TEXCOORD0;
                //float2 uv : TEXCOORD1;
                float2 aouv : TEXCOORD4;


            };

            sampler2D _MainTex;
            float4 _MainTex_ST;

            v2f vert (appdata v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                //o.uv = TRANSFORM_TEX(v.uv0, _MainTex);
                o.aouv = TRANSFORM_TEX(v.uv0, _AOTexture);
                return o;
            }

            fixed4 frag (v2f i) : COLOR
            {
                // sample the texture
                //fixed4 col = tex2D(_MainTex, i.pos)*_Color;

                // sample color only.
                fixed4 col = _Color;

                // apply AO
                half4 AOTexVar = lerp(half4(_AOColor, 1), half4(whiteColor, 1), lerp(half4(1,1,1,1), tex2D(_AOTexture, i.aouv), _AOPower));
                col *= AOTexVar;

                return col;
            }
            ENDCG
        }
    }
}