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🖌️ Tools & Brushes

Tools are the final stage of the painting pipeline — they poll the surface's StampBatch each frame and dispatch GPU draw commands to the PaintEngine.

Pull-Based Design

Tools don't receive events — they poll the surface's StampBatch every frame. The surface clears its batch in LateUpdate after all consumers have processed it. This decouples tools from triggers and allows multiple tools to read the same batch.

🏗️ Tool Hierarchy​

BaseTool (abstract)
├── StandardTool
│   └── StandardBrush          — Default painting brush
└── ForceTool
    ├── DirectionalForceBrush  — Force in fixed UV-space direction
    ├── RadialForceBrush       — Radial push/pull with optional swirl
    └── TextureForceBrush      — Texture-driven force field
  • BaseTool defines the abstract interface for all tools, including stamp processing and GPU dispatch.
  • StandardTool / StandardBrush handles color, normal, and PBR channel painting.
  • ForceTool and its subclasses apply velocity/force fields to fluid simulation layers.

🎨 StandardBrush Channels​

The StandardBrush exposes an array of channels, each controlling a different PBR texture layer. Configure channels programmatically for dynamic painting:

// Cấu hình channel — thiết lập brush vẽ màu đỏ với texture tùy chỉnh
var channel = brush.Channels[0];
channel.Intensity = 1.0f;
channel.Value.ColorValue = Color.red;
channel.Texture = myBrushTexture;
channel.Value.ValueMode = ValueMode.Dynamic;

Each channel supports:

  • Intensity — Strength of the paint application (0 – 1)
  • Value — The color or scalar value to paint, with configurable ValueMode
  • Texture — Optional brush texture mask for stamp shape
  • Blend Mode — Per-channel blend mode (Normal, Multiply, Add, etc.)

💨 ForceBrush Shader Passes​

Force brushes drive fluid simulation by writing velocity data into force textures. Each brush type maps to a specific shader pass:

Brush TypePassDescription
RadialForceBrush (Push)0Push fluid outward from stamp center
RadialForceBrush (Push + Swirl)1Push outward with rotational component
RadialForceBrush (Pull)2Pull fluid inward toward stamp center
RadialForceBrush (Pull + Swirl)3Pull inward with rotational component
DirectionalForceBrush4Apply force in a fixed UV-space direction
tip

Use Push + Swirl (Pass 1) for realistic paint mixing effects. The swirl component adds rotational turbulence that prevents uniform radial spreading.

🔧 Tool Configuration Best Practices​

  • Tools are designed to be one active at a time — disable all tools before enabling the selected one.
  • Each tool reads from the surface's StampBatch, so ensure the surface is properly activated before the tool processes stamps.
  • Force brushes only affect surfaces that have an active fluid simulation committer attached.

Previous: Triggers & Strokes | Next: Committers & Fluid Simulation