chameleon/Assets/Scripts/MeshPainter.Spray.cs

using UnityEngine;

public partial class MeshPainter
{
    // --- Spray can brush ---
    //
    // Instead of one solid stamp, the spray scatters many small dots (random position,
    // size and alpha) within the brush footprint. It is implemented by baking those dots
    // into a fresh procedural MASK each stamp and then painting that mask with ONE normal
    // brush stamp. This reuses the entire seam-bridging / curvature-following / per-channel
    // pipeline as-is and costs a single mesh draw per stamp (not one per dot). Because the
    // per-dot alpha lives in the mask value, it flows into every channel (albedo, mask map,
    // emission) automatically - on both the GPU and CPU backends.

    [Header("Brush - spray can")]
    [Tooltip("Spray-can mode: scatter random dots (position, size, alpha) within the brush " +
             "radius instead of a single solid stamp. The dots are baked into the brush mask, " +
             "so this works on all channels and both backends.")]
    public bool spray = false;

    [Tooltip("Number of dots scattered per stamp.")]
    [Range(1, 128)]
    public int sprayDots = 24;

    [Tooltip("Dot diameter as a fraction of the brush diameter (randomized per dot between min and max).")]
    [Range(0.01f, 1f)]
    public float sprayDotSizeMin = 0.05f;

    [Tooltip("Dot diameter as a fraction of the brush diameter (randomized per dot between min and max).")]
    [Range(0.01f, 1f)]
    public float sprayDotSizeMax = 0.18f;

    [Tooltip("Per-dot opacity (randomized per dot between min and max). Multiplied on top of the channel color's alpha.")]
    [Range(0f, 1f)]
    public float sprayDotAlphaMin = 0.25f;

    [Tooltip("Per-dot opacity (randomized per dot between min and max). Multiplied on top of the channel color's alpha.")]
    [Range(0f, 1f)]
    public float sprayDotAlphaMax = 1f;

    // Resolution of the per-stamp spray mask (square). Small + reused so regenerating it
    // every stamp stays cheap.
    private const int SprayRes = 128;
    private const float SprayDotSoftEdge = 0.4f; // fraction of the dot radius that fades to 0

    private Texture2D _sprayTex;        // the baked spray mask uploaded to the brush
    private Color32[] _sprayPixels;     // reused upload buffer
    private float[] _sprayOpacity;      // reused per-texel opacity (CPU sampling)

    // --- Active stamp mask (indirection shared by both backends) ---
    // The standard mask cache (_resolvedMask / _maskOpacity / _maskW / _maskH) stays the
    // canonical resolved mask used by the preview. _stamp* is what the CURRENT stamp paints
    // with - the resolved mask for normal painting, or a fresh spray mask in spray mode.
    private Texture2D _stampMask;
    private float[] _stampOpacity;
    private int _stampW, _stampH;

    /// <summary>Points the active stamp mask at the resolved standard mask (normal painting).</summary>
    private void UseResolvedStampMask()
    {
        _stampMask = _resolvedMask;
        _stampOpacity = _maskOpacity;
        _stampW = _maskW;
        _stampH = _maskH;
    }

    /// <summary>
    /// Bakes a fresh random spray pattern into the spray mask and makes it the active stamp
    /// mask. Each dot gets a random center inside the brush disc, a random diameter and a
    /// random opacity; dots composite by max so overlaps never exceed full opacity.
    /// </summary>
    private void BuildSprayStampMask()
    {
        EnsureSprayBuffers();

        System.Array.Clear(_sprayOpacity, 0, _sprayOpacity.Length);

        int dots = Mathf.Max(1, sprayDots);
        float sizeLo = Mathf.Clamp(Mathf.Min(sprayDotSizeMin, sprayDotSizeMax), 0.01f, 1f);
        float sizeHi = Mathf.Clamp(Mathf.Max(sprayDotSizeMin, sprayDotSizeMax), 0.01f, 1f);
        float alphaLo = Mathf.Clamp01(Mathf.Min(sprayDotAlphaMin, sprayDotAlphaMax));
        float alphaHi = Mathf.Clamp01(Mathf.Max(sprayDotAlphaMin, sprayDotAlphaMax));

        for (int k = 0; k < dots; k++)
        {
            // Diameter is a fraction of the brush diameter -> uv radius = fraction * 0.5.
            float dotR = Mathf.Max(0.5f / SprayRes, Random.Range(sizeLo, sizeHi) * 0.5f);
            float alpha = Random.Range(alphaLo, alphaHi);
            // Keep the WHOLE dot inside the brush disc (uv radius 0.5 = the brush radius) so the
            // spray footprint matches the normal brush instead of bleeding past it by dotR.
            float centerR = Mathf.Max(0f, 0.5f - dotR);
            Vector2 c = Random.insideUnitCircle * centerR + new Vector2(0.5f, 0.5f);

            SplatDot(c.x, c.y, dotR, alpha);
        }

        for (int i = 0; i < _sprayOpacity.Length; i++)
        {
            byte g = (byte)(Mathf.Clamp01(_sprayOpacity[i]) * 255f + 0.5f);
            _sprayPixels[i] = new Color32(g, g, g, 255);
        }
        _sprayTex.SetPixels32(_sprayPixels);
        _sprayTex.Apply(false);

        _stampMask = _sprayTex;
        _stampOpacity = _sprayOpacity;
        _stampW = SprayRes;
        _stampH = SprayRes;
    }

    /// <summary>Rasterizes one soft dot (center/radius in uv, value = alpha) into the opacity buffer, compositing by max.</summary>
    private void SplatDot(float cx, float cy, float r, float alpha)
    {
        if (alpha <= 0f) return;

        float inner = 1f - SprayDotSoftEdge; // solid core up to this normalized distance, then fade
        int minX = Mathf.Max(0, Mathf.FloorToInt((cx - r) * SprayRes));
        int maxX = Mathf.Min(SprayRes - 1, Mathf.CeilToInt((cx + r) * SprayRes));
        int minY = Mathf.Max(0, Mathf.FloorToInt((cy - r) * SprayRes));
        int maxY = Mathf.Min(SprayRes - 1, Mathf.CeilToInt((cy + r) * SprayRes));
        float invR = 1f / r;

        for (int y = minY; y <= maxY; y++)
        {
            float vY = (y + 0.5f) / SprayRes;
            int row = y * SprayRes;
            for (int x = minX; x <= maxX; x++)
            {
                float vX = (x + 0.5f) / SprayRes;
                float dx = vX - cx, dy = vY - cy;
                float dist = Mathf.Sqrt(dx * dx + dy * dy) * invR; // 0 = center, 1 = edge
                if (dist >= 1f) continue;

                float falloff = dist <= inner ? 1f : 1f - Mathf.SmoothStep(inner, 1f, dist);
                float val = alpha * falloff;
                int idx = row + x;
                if (val > _sprayOpacity[idx]) _sprayOpacity[idx] = val;
            }
        }
    }

    private void EnsureSprayBuffers()
    {
        if (_sprayTex) return;

        _sprayTex = NewMaskTexture(SprayRes, "MeshPainter_SprayMask");
        _sprayPixels = new Color32[SprayRes * SprayRes];
        _sprayOpacity = new float[SprayRes * SprayRes];
    }

    private void TeardownSpray()
    {
        if (_sprayTex) { Destroy(_sprayTex); _sprayTex = null; }
        _sprayPixels = null;
        _sprayOpacity = null;
    }
}