Shader "Custom/EmissiveLaser"
{
    Properties
    {
        _MainTex      ("Texture", 2D) = "white" {}
        [HDR]_Color   ("Tint Color (HDR)", Color) = (1, 0, 0, 1)
        _Emission     ("Emission Strength", Range(0, 20)) = 5.0
        _ScrollSpeed  ("Scroll Speed", Float) = 1.0

        // Optional niceties for a neon line look:
        _CoreSharpness("Core Sharpness", Range(0.1, 8)) = 2.0   // higher = tighter core
        _EdgeSoftness ("Edge Softness",  Range(0.0, 1.0)) = 0.35 // higher = wider glow band
    }

    SubShader
    {
        Tags { "Queue"="Transparent" "RenderType"="Transparent" }
        LOD 100

        // Additive neon
        Blend One One
        ZWrite Off
        Cull Off
        Lighting Off
        // Keep normal depth test so it can be occluded by geometry
        ZTest LEqual

        Pass
        {
            CGPROGRAM
            #pragma vertex   vert
            #pragma fragment frag
            #pragma target   3.0
            #include "UnityCG.cginc"
            #pragma multi_compile_fog

            sampler2D _MainTex;
            float4 _MainTex_ST;

            float4 _Color;
            float  _Emission;
            float  _ScrollSpeed;

            float  _CoreSharpness;
            float  _EdgeSoftness;

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

            struct v2f
            {
                float4 pos : SV_POSITION;
                float2 uv  : TEXCOORD0;
                UNITY_FOG_COORDS(1)
            };

            v2f vert (appdata v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);

                // Scroll along U
                float2 uv = TRANSFORM_TEX(v.uv, _MainTex);
                uv.x += _Time.y * _ScrollSpeed;
                o.uv = uv;

                UNITY_TRANSFER_FOG(o, o.pos);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // Base texture (use white if you just want a flat color)
                fixed4 tex = tex2D(_MainTex, i.uv);

                // Neon falloff across the width (LineRenderer typically uses V for width 0..1)
                // Center at 0.5; make a soft bell curve controlled by edge softness & sharpness.
                float v = abs(i.uv.y - 0.5) * 2.0;                  // 0 at center, 1 at edges
                float core = pow(saturate(1.0 - v / max(1e-4, _EdgeSoftness + 1e-4)), _CoreSharpness);
                // Clamp a little to avoid banding
                core = saturate(core);

                // HDR output: bright enough for Bloom to catch (Camera HDR must be ON)
                float3 rgb = tex.rgb * _Color.rgb * (_Emission);

                // Multiply by our soft core so edges fade nicely
                rgb *= core;

                // Additive blending ignores alpha, but keep it tidy
                return fixed4(rgb, tex.a * _Color.a);
            }
            ENDCG
        }
    }
}