unity – How can I align the moon halo to the illuminated a part of the moon in a customized skybox shader?

I created a customized skybox shader that includes a black sky with solely the moon and its halo. The moon responds realistically to the scene’s directional mild (daylight), which creates a convincing impact. Nevertheless, for a while now, I’ve been attempting to use the identical impact to the halo in order that it resembles the moon, but it surely hasn’t labored.

And I need is to make the middle of the moon’s illuminated half the place of the middle of seen half from the halo, in order that the halo at all times seems centered on the lit portion of the moon, which might make it look extra practical — however all my makes an attempt have failed.

To manage the moon’s route and simulate practical lighting, I exploit a easy script that passes two parameters to the shader globally:

_MoonDir: the moon’s ahead route in world area, used to orient the moon within the sky and decide its obvious place from the digital camera.

_MoonSpaceMatrix: a change matrix constructed from the moon’s proper, up, and ahead vectors. That is used to accurately rework normals into moon-local area and pattern the moon texture accordingly.

The script runs each body and ensures that the shader at all times receives the proper orientation and alignment of the moon relative to the scene’s mild supply (usually the sun). This setup makes it potential to use directional lighting to the moon floor.

Is it potential to use daylight impact to the halo (as it’s finished for the moon) and align the middle of its seen half (after making use of the impact) with the middle of the moon’s illuminated space?

Observe:
I exploit Texture2D for each the moon and the halo to maintain the shader light-weight, as I intend to apply it to cell gadgets.

• The moon itself is simply rendered as a white circle — no texture element is required at present.
• The halo texture is an easy clear radial gradient:

Shader Code:

Shader "Skybox/SimpleSkybox_Moon"
{
    Properties
    {
        _SkyColor ("Sky Shade", Shade) = (0,0,0,1)

        [space(10)]

        [NoScaleOffset]_MoonTex ("Moon Texture 2D", 2D) = "white" {}
        _MoonSize ("Moon Dimension", Vary(0.1,20)) = 9
        _MoonTint ("Moon Tint", Shade) = (1,1,1,1)
        _MoonExposure ("Moon Publicity", Vary(-6,6)) = 1

        [NoScaleOffset]_MoonHaloTex ("Moon Halo Texture 2D", 2D) = "white" {}
        _MoonHaloSize ("Moon Halo Dimension", Vary(1, 10)) = 1.7
        _MoonHaloExposure ("Moon Halo Publicity", Vary(-6, 6)) = -4
        _MoonHaloFadeThreshold ("Moon Halo Fade Threshold", Vary(0.01,1)) = 0.186
    }

    SubShader
    {
        Tags { "Queue"="Background" "RenderType"="Opaque" }
        Cull Off ZWrite Off ZTest All the time // No depth testing or writing, since it is a skybox

        Go
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #embrace "UnityCG.cginc"

            // Sky and moon parameters
            fixed4   _SkyColor;

            sampler2D _MoonTex;
            float    _MoonSize;
            fixed4   _MoonTint;
            float    _MoonExposure;

            float3   _MoonDir; // Moon route in world area (set by script)
            float4x4 _MoonSpaceMatrix; // Transforms route to moon UV area (set by script)

            sampler2D _MoonHaloTex;
            float _MoonHaloSize;
            float _MoonHaloExposure;
            float _MoonHaloFadeThreshold;

            // Enter vertex construction
            struct appdata { float4 vertex : POSITION; };
            struct v2f      { float4 pos : SV_POSITION; float3 vDir : TEXCOORD0; };

            // Vertex shader: outputs view route in world area
            v2f vert(appdata v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.vDir = normalize(mul((float3x3)unity_ObjectToWorld, v.vertex.xyz));
                return o;
            }

            // Intersect ray with sphere (for moon visibility)
            float sphIntersect(float3 rayDir, float3 heart, float r)
            {
                float3 oc = -center;
                float  b  = dot(oc, rayDir);
                float  c  = dot(oc, oc) - r*r;
                float  h  = b*b - c;
                if (h < 0) return -1;
                h = sqrt(h);
                float t = -b - h;
                return t < 0 ? -1 : t;
            }

            // Compute the moon halo look based mostly on view angle and publicity
            float3 GetMoonHalo(float3 viewDir, float3 dir, float dimension, float moonSize, float moonMask, float moonNdotL)
            {
                float cosAngle = dot(viewDir, normalize(dir));
                float maxCosAngle = cos(radians(moonSize) * dimension);
                float r = saturate((1.0 - cosAngle) / (1.0 - maxCosAngle));
                float2 haloUV = float2(0.5 + r * 0.5, 0.5);

                float haloMask = r <= 1.0 ? 1.0 : 0.0;

                // Non-compulsory fade-out when moon is illuminated
                float haloFade = 1.0;
                if (moonMask > 0.0)
                    haloFade = saturate(1.0 - moonNdotL / _MoonHaloFadeThreshold);

                float3 haloColor = tex2D(_MoonHaloTex, haloUV).rgb;
                return haloColor * _MoonTint.rgb * exp2(_MoonHaloExposure) * haloMask * haloFade;
            }

            // Fragment shader: determines remaining pixel coloration
            fixed4 frag(v2f i) : SV_Target
            {
                float3 viewDir = normalize(-i.vDir); // View route from digital camera
                float3 moonDir = normalize(_MoonDir); // Moon route
                float  rad     = tan(radians(_MoonSize)); // Moon radius (angular)

                float t = sphIntersect(viewDir, moonDir, rad); // Ray-sphere intersection
                float moonMask = t > 0 ? 1.0 : 0.0;

                float3 moonColor = 0;
                float  moonNdotL = 0;
                if (moonMask > 0.0)
                {
                    float3 hitPt = viewDir * t;
                    float3 moonNormal = normalize(hitPt - moonDir);

                    // Convert moon regular to texture UVs
                    float3 localDir = mul(_MoonSpaceMatrix, float4(moonNormal,0)).xyz;
                    float2 uv = localDir.xy * 0.5 + 0.5;
                    uv.y = 1.0 - uv.y;

                    if (all(uv >= 0.0) && all(uv <= 1.0))
                    {
                        float3 texCol = tex2D(_MoonTex, uv).rgb;
                        float3 lightDir = normalize(-_WorldSpaceLightPos0.xyz); // Directional mild
                        moonNdotL = saturate(dot(moonNormal, lightDir)); // Lighting issue
                        moonColor = texCol * moonNdotL * _MoonTint.rgb * exp2(_MoonExposure); // Ultimate moon lighting
                    }
                }

                // Compute the moon halo
                float3 moonHalo = GetMoonHalo(viewDir, _MoonDir, _MoonHaloSize, _MoonSize, moonMask, moonNdotL);

                // Ultimate sky coloration = base sky + moon + halo
                float3 col = _SkyColor + moonColor + moonHalo;

                return float4(col, 1);
            }
            ENDCG
        }
    }
    FallBack Off
}

The script code to set the moon’s route and matrix knowledge:

utilizing UnityEngine;

// Ensures this script runs in Edit Mode (contained in the editor, with out hitting Play)
[ExecuteInEditMode]
public class MoonShaderController : MonoBehaviour
{
    // Reference to the moon object within the scene (should be set within the Inspector)
    [SerializeField] Remodel _moon;

    // Shader property identify for moon route (as seen within the shader)
    [SerializeField] string _moonDirId = "_MoonDir";

    // Shader property identify for the matrix used to transform world route to UV area
    [SerializeField] string _moonSpaceMatrixId = "_MoonSpaceMatrix";

    // Referred to as in any case Replace() features — helpful for digital camera/sky updates
    void LateUpdate()
    {
        if (_moon)
        {
            // Passes the moon's ahead vector to the shader (_MoonDir), which represents its route in world area
            Shader.SetGlobalVector(_moonDirId, _moon.rework.ahead);

            // Constructs a change matrix from the moon's native axes (proper, up, ahead)
            // and transposes it to align with the shader's anticipated coordinate area
            Shader.SetGlobalMatrix(_moonSpaceMatrixId,
                new Matrix4x4(
                    _moon.rework.proper,   // X-axis
                    _moon.rework.up,      // Y-axis
                    _moon.rework.ahead, // Z-axis
                    Vector4.zero             // No translation
                ).transpose
            );
        }
    }
}