chameleon/Assets/Scripts/MeshPainter.Setup.cs

using UnityEngine;

public partial class MeshPainter
{
    // --- Setup (shared) ---

    private void SetupCollider()
    {
        _collider = GetComponent<MeshCollider>();
        if (!_collider) _collider = gameObject.AddComponent<MeshCollider>();
        _collider.convex = false; // non-convex provides triangleIndex / textureCoord

        _bakedMesh = new Mesh { name = "MeshPainter_Baked" };
        BakeColliderMesh();
    }

    private void BakeColliderMesh()
    {
        if (_skinned)
        {
            // Static skinned mesh: bake into local coordinates (scale = 1).
            _skinned.BakeMesh(_bakedMesh);
            _collider.sharedMesh = null;
            _collider.sharedMesh = _bakedMesh;
        }
        else
        {
            var mf = GetComponent<MeshFilter>();
            if (mf) _collider.sharedMesh = mf.sharedMesh;
        }
    }

    /// <summary>Reads vertices/triangles/UVs of the collider mesh and computes culling data.</summary>
    private void BuildMeshCaches()
    {
        Mesh m = _collider.sharedMesh;
        if (!m) return;

        _verts = m.vertices;
        _tris = m.triangles;
        _uvs = m.uv;

        // Fallback to the original mesh UVs if the baked mesh dropped them.
        if ((_uvs == null || _uvs.Length != _verts.Length) && _skinned && _skinned.sharedMesh)
            _uvs = _skinned.sharedMesh.uv;

        if (_uvs == null || _uvs.Length != _verts.Length) return;

        int triCount = _tris.Length / 3;
        _triCenter = new Vector3[triCount];
        _triRadius = new float[triCount];

        double sumArea3D = 0.0, sumAreaUv = 0.0;

        for (int t = 0; t < triCount; t++)
        {
            int i0 = _tris[t * 3], i1 = _tris[t * 3 + 1], i2 = _tris[t * 3 + 2];
            Vector3 a = _verts[i0], b = _verts[i1], c = _verts[i2];

            Vector3 center = (a + b + c) / 3f;
            _triCenter[t] = center;
            float ra = (a - center).sqrMagnitude;
            float rb = (b - center).sqrMagnitude;
            float rc = (c - center).sqrMagnitude;
            _triRadius[t] = Mathf.Sqrt(Mathf.Max(ra, Mathf.Max(rb, rc)));

            sumArea3D += 0.5 * Vector3.Cross(b - a, c - a).magnitude;
            Vector2 ua = _uvs[i0], ub = _uvs[i1], uc = _uvs[i2];
            sumAreaUv += 0.5 * Mathf.Abs(Cross2D(ub - ua, uc - ua));
        }

        if (sumAreaUv > 1e-9) _avgUvToLocal = (float)System.Math.Sqrt(sumArea3D / sumAreaUv);
    }

    /// <summary>
    /// Rasterizes the mesh UV islands into a per-texel coverage marker (true = the texel lies
    /// inside a UV triangle). This is the dilation SOURCE / overwrite guard: island texels are
    /// real content the edge-padding pass must never overwrite, while the gutter (false) stays
    /// paddable. Deriving the marker from the STATIC UV layout - instead of from transient
    /// per-stroke coverage - makes every seed (fresh start, loaded maps, backend switch) mark
    /// the same real content as painted, so the first stroke after a load/switch no longer
    /// bleeds over the existing paint. Built once and cached (UV layout + textureSize are fixed).
    /// </summary>
    private bool[] GetIslandMask()
    {
        int n = textureSize * textureSize;
        if (_islandMask != null && _islandMask.Length == n) return _islandMask;

        var mask = new bool[n];
        if (_tris == null || _uvs == null) { _islandMask = mask; return mask; }

        float ts = textureSize;
        const float eps = -1e-4f; // matches PaintStamp3D: tolerate 1px cracks between triangles
        int triCount = _tris.Length / 3;

        for (int t = 0; t < triCount; t++)
        {
            int i0 = _tris[t * 3], i1 = _tris[t * 3 + 1], i2 = _tris[t * 3 + 2];
            Vector2 uv0 = _uvs[i0], uv1 = _uvs[i1], uv2 = _uvs[i2];

            float p0x = uv0.x * ts, p0y = uv0.y * ts;
            float p1x = uv1.x * ts, p1y = uv1.y * ts;
            float p2x = uv2.x * ts, p2y = uv2.y * ts;

            int minX = Mathf.Clamp(Mathf.FloorToInt(Mathf.Min(p0x, Mathf.Min(p1x, p2x))), 0, textureSize - 1);
            int maxX = Mathf.Clamp(Mathf.CeilToInt(Mathf.Max(p0x, Mathf.Max(p1x, p2x))), 0, textureSize - 1);
            int minY = Mathf.Clamp(Mathf.FloorToInt(Mathf.Min(p0y, Mathf.Min(p1y, p2y))), 0, textureSize - 1);
            int maxY = Mathf.Clamp(Mathf.CeilToInt(Mathf.Max(p0y, Mathf.Max(p1y, p2y))), 0, textureSize - 1);
            if (maxX < minX || maxY < minY) continue;

            float d = (p1y - p2y) * (p0x - p2x) + (p2x - p1x) * (p0y - p2y);
            if (Mathf.Abs(d) < 1e-7f) continue;
            float invD = 1f / d;

            for (int y = minY; y <= maxY; y++)
            {
                float py = y + 0.5f;
                int row = y * textureSize;
                for (int x = minX; x <= maxX; x++)
                {
                    float px = x + 0.5f;
                    float a = ((p1y - p2y) * (px - p2x) + (p2x - p1x) * (py - p2y)) * invD;
                    if (a < eps) continue;
                    float b = ((p2y - p0y) * (px - p2x) + (p0x - p2x) * (py - p2y)) * invD;
                    if (b < eps) continue;
                    if (1f - a - b < eps) continue;
                    mask[row + x] = true;
                }
            }
        }

        _islandMask = mask;
        return mask;
    }

    /// <summary>Builds the per-map seed colors (in canonical/material layout) from the existing material.</summary>
    private void BuildSeedColors()
    {
        _seedCanonical = new Color32[MAP_COUNT][];
        _seedCanonical[MAP_ALBEDO] = BuildBaseColors();

        // Mask map seed from the material scalars: R = metallic, G = occlusion (255 =
        // unoccluded, so the look is unchanged until painted), B = 0, A = smoothness.
        float metallic0 = _materialInstance.HasProperty(MetallicId) ? _materialInstance.GetFloat(MetallicId) : 0f;
        float smoothness0 = _materialInstance.HasProperty(SmoothnessId) ? _materialInstance.GetFloat(SmoothnessId) : 0.5f;
        _seedCanonical[MAP_MSO] = FillCanonical(new Color32(
            (byte)(Mathf.Clamp01(metallic0) * 255f), 255, 0, (byte)(Mathf.Clamp01(smoothness0) * 255f)));

        // Emission: keep the existing look (black if the material's emission is off).
        Color emission0 = Color.black;
        if (_materialInstance.HasProperty(EmissionColorId) &&
            (_materialInstance.globalIlluminationFlags & MaterialGlobalIlluminationFlags.EmissiveIsBlack) == 0)
            emission0 = _materialInstance.GetColor(EmissionColorId);
        _seedCanonical[MAP_EM] = FillCanonical(new Color32(
            (byte)(Mathf.Clamp01(emission0.r) * 255f),
            (byte)(Mathf.Clamp01(emission0.g) * 255f),
            (byte)(Mathf.Clamp01(emission0.b) * 255f), 255));
    }

    private Color32[] FillCanonical(Color32 c)
    {
        var px = new Color32[textureSize * textureSize];
        for (int i = 0; i < px.Length; i++) px[i] = c;
        return px;
    }

    /// <summary>Builds the albedo base-color texels from the existing material texture or baseColor.</summary>
    private Color32[] BuildBaseColors()
    {
        var px = new Color32[textureSize * textureSize];

        Texture sourceTex = null;
        var shared = _renderer.sharedMaterial;
        if (shared)
        {
            if (shared.HasProperty(BaseMapId)) sourceTex = shared.GetTexture(BaseMapId);
            if (!sourceTex && shared.HasProperty(MainTexId)) sourceTex = shared.GetTexture(MainTexId);
        }

        var src = sourceTex as Texture2D;
        if (src)
        {
            try
            {
                if (src.width == textureSize && src.height == textureSize && src.isReadable)
                    return src.GetPixels32();
            }
            catch { /* not readable -> fall back to baseColor */ }
        }

        Color32 c = baseColor;
        for (int i = 0; i < px.Length; i++) px[i] = c;
        return px;
    }

    /// <summary>Enables the URP keywords for the painted PBR maps and seeds the material scalars.</summary>
    private void ConfigureMaterialPbr()
    {
        if (!_materialInstance) return;

        // Metallic-smoothness map: metallic from R, smoothness from the map's alpha
        // (NOT the albedo alpha) scaled by _Smoothness (= 1 so the map drives it as-is).
        if (_materialInstance.HasProperty(MetallicGlossMapId))
        {
            _materialInstance.EnableKeyword("_METALLICSPECGLOSSMAP");
            _materialInstance.DisableKeyword("_SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A");
            if (_materialInstance.HasProperty(SmoothnessId)) _materialInstance.SetFloat(SmoothnessId, 1f);
        }

        // Emission map x _EmissionColor (white * intensity). Clear the "emissive is black"
        // GI flag so the emission is actually used.
        if (_materialInstance.HasProperty(EmissionMapId))
        {
            _materialInstance.EnableKeyword("_EMISSION");
            _materialInstance.globalIlluminationFlags = MaterialGlobalIlluminationFlags.RealtimeEmissive;
            RefreshEmissionColor();
        }

        // Occlusion map: URP samples the G channel (LerpWhiteTo(map.g, _OcclusionStrength)).
        // Strength 1 so the painted value drives the occlusion as-is.
        if (_materialInstance.HasProperty(OcclusionMapId))
        {
            _materialInstance.EnableKeyword("_OCCLUSIONMAP");
            if (_materialInstance.HasProperty(OcclusionStrengthId)) _materialInstance.SetFloat(OcclusionStrengthId, 1f);
        }
    }

    /// <summary>Pushes the global emission intensity to the material's _EmissionColor (live-tunable).</summary>
    private void RefreshEmissionColor()
    {
        if (_materialInstance && _materialInstance.HasProperty(EmissionColorId))
            _materialInstance.SetColor(EmissionColorId, Color.white * Mathf.Max(0f, emissionIntensity));
    }
}