Shader for showing a drink with various fill levels in Unity. Instancing enabled.

DrinkShader.shader

Shader "Unlit/DrinkShader"
{
	Properties
	{
		[PerRendererData] _MainTex ("Texture", 2D) = "white" {}
		[PerRendererData] _FillTex("FillTexture", 2D) = "white" {}
		[PerRendererData] _FillAmount("Fill", Range(0.0,1.0)) = 1.0
		[HideInInspector] _RendererColor("RendererColor", Color) = (1,1,1,1)
		[MaterialToggle] PixelSnap("Pixel Snap", Float) = 0
	}

	SubShader
	{
		Tags {
			"Queue" = "Transparent"
			"IgnoreProjector" = "True"
			"RenderType" = "Transparent"
			"PreviewType" = "Plane"
			"CanUseSpriteAtlas" = "True"
		}

		Cull Off
		Lighting Off
		ZWrite Off
		Blend SrcAlpha OneMinusSrcAlpha

		Pass
		{
		CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma target 2.0
			#pragma multi_compile_instancing
			#pragma multi_compile_local _ PIXELSNAP_ON

			#include "UnityCG.cginc"

#ifndef UNITY_SPRITES_INCLUDED
#define UNITY_SPRITES_INCLUDED

#ifdef UNITY_INSTANCING_ENABLED
			UNITY_INSTANCING_BUFFER_START(PerDrawSprite)
				UNITY_DEFINE_INSTANCED_PROP(fixed4, unity_SpriteRendererColorArray)
				UNITY_DEFINE_INSTANCED_PROP(fixed2, unity_SpriteFlipArray)
			UNITY_INSTANCING_BUFFER_END(PerDrawSprite)

			#define _RendererColor  UNITY_ACCESS_INSTANCED_PROP(PerDrawSprite, unity_SpriteRendererColorArray)
			#define _Flip           UNITY_ACCESS_INSTANCED_PROP(PerDrawSprite, unity_SpriteFlipArray)
#endif

			UNITY_INSTANCING_BUFFER_START(MyProps)
				UNITY_DEFINE_INSTANCED_PROP(float, _FillAmount)
			UNITY_INSTANCING_BUFFER_END(MyProps)

			CBUFFER_START(UnityPerDrawSprite)
#ifndef UNITY_INSTANCING_ENABLED
			fixed4 _RendererColor;
			fixed2 _Flip;
#endif
			CBUFFER_END

			// Material Color
			fixed4 _Color;

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

			struct v2f
			{
				float4 vertex : SV_POSITION;
				fixed4 color : COLOR;
				float2 uv : TEXCOORD0;
				UNITY_VERTEX_INPUT_INSTANCE_ID
			};

			inline float4 UnityFlipSprite(in float3 pos, in fixed2 flip)
			{
				return float4(pos.xy * flip, pos.z, 1.0);
			}

			v2f vert (appdata v)
			{
				v2f o;

				UNITY_SETUP_INSTANCE_ID(v);
				UNITY_TRANSFER_INSTANCE_ID(v, o);

				o.vertex = UnityFlipSprite(v.vertex, _Flip);
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = v.uv;
				o.color = v.color * _Color * _RendererColor;

#ifdef PIXELSNAP_ON
				o.vertex = UnityPixelSnap(o.vertex);
#endif
				return o;
			}

			sampler2D _MainTex;
			sampler2D _FillTex;

			fixed4 frag(v2f i) : SV_Target
			{
				UNITY_SETUP_INSTANCE_ID(i);
				fixed4 mainCol = tex2D(_MainTex, i.uv);
				fixed4 fillCol = tex2D(_FillTex, i.uv);

				// TODO: way to do this without branching? does it matter?
				if (i.uv.y > UNITY_ACCESS_INSTANCED_PROP(MyProps, _FillAmount))
					return mainCol;

				return fillCol;
			}
#endif // UNITY_SPRITES_INCLUDED
		ENDCG
		}
	}
}