📚 Channels & Layers

Multi-channel PBR painting with per-channel blend modes and multi-layer compositing.

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📝 ChannelDefinition (ScriptableObject)

Each channel is defined by a ChannelDefinition asset specifying what material property it controls:

Field	Description
ShaderProperty	Material texture slot name (e.g. _MainTex, _BumpMap)
ValueType	Color, Normal, or Scalar
ChannelMask	Which RGBA components to write (flags)
IsSRGB	Whether to use sRGB color space (Color only)
EnableDynamicsTarget	Allocates RT1 for fluid simulation velocity+mass

Creating a ChannelDefinition

Right-click in the Project window:

Create → Deepwave / Simple Painter / Channel Definition

Common Configurations

Channel	ShaderProperty	ValueType	ChannelMask	IsSRGB
Albedo	_MainTex	Color	RGBA	✅
Normal	_BumpMap	Normal	RGBA	❌
Metallic	_MetallicGlossMap	Scalar	R	❌
Roughness	_MetallicGlossMap	Scalar	A	❌

EnableDynamicsTarget

Set EnableDynamicsTarget = true only on the primary channel that drives fluid simulation. This allocates an additional RT1 render target for velocity+mass data. Enabling it unnecessarily wastes GPU memory.

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🎨 PaintChannel

A runtime instance linked to a ChannelDefinition. Contains multiple PaintLayers and a ScratchBuffer.

// Lấy channel từ surface
var channel = paintSurface.GetChannel(albedoChannelDef);

// Truy cập danh sách layers
var layers = channel.Layers;

// Đặt layer đang hoạt động để vẽ
channel.ActiveLayerIndex = 2;

// Đánh dấu channel cần re-composition
channel.SetDirty();

SetDirty

Call SetDirty() whenever you programmatically modify a channel's layers (visibility, opacity, blend mode). This triggers the ChannelGroup to enqueue a ChannelCompositeCommand for re-compositing.

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🗂️ PaintLayer

Each layer owns a GPU ManagedRenderTarget and has independent visibility, opacity, blend mode, and an optional initial texture:

Property	Description
IsVisible	Toggle layer visibility (triggers re-composition)
Opacity	Layer opacity, 0–1
ColorBlendMode	Blend mode for Color channels
ScalarBlendMode	Blend mode for Scalar channels
NormalBlendMode	Blend mode for Normal channels
InitTexture	Optional starting texture (applied on Reset)

Blend Mode Types

Blend modes are type-specific to prevent invalid combinations:

• Color: Normal, Multiply, Add, Min, Max, Screen, Overlay, SoftLight
• Scalar: Normal, Multiply, Add, Min, Max
• Normal: Lerp, RNM, UDN, Whiteout, Overlay, MaxSlope, Subtract

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✏️ ScratchBuffer

The "draft" layer holding the current brush stroke before it's committed:

• RT0 (Visual) — The painted value (what you see during the stroke)
• RT1 (Dynamics) — Optional simulation target (velocity + mass for fluid effects). Only allocated when EnableDynamicsTarget = true
• BlendDeposition — Positive values add coverage, negative values erase. Set by the committer.

Stroke in progress:
┌─────────────────────────────────────┐
│  RT0 (Visual)  │  RT1 (Dynamics)   │
│  Color/Normal  │  Velocity + Mass  │
│  values        │  (optional)       │
└─────────────────────────────────────┘
         │ BlendDeposition (+1 = draw, -1 = erase)
         ▼
    PaintLayer (persistent)

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🔄 Compositing Flow

How Compositing Works

When a channel is dirty, ChannelGroup enqueues a ChannelCompositeCommand during the Composition phase. It composites:

1. Origin texture (the original material texture)
2. + All visible layers (bottom to top, with per-layer blend modes)
3. + Scratch buffer (the current in-progress stroke)
4. → Final composite render target (set on the material)

This happens every frame that a channel is marked dirty, ensuring real-time visual feedback during painting.

Compositing Order

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💡 Usage Examples

Adding a New Layer at Runtime

// Lấy channel và thêm layer mới
var channel = paintSurface.GetChannel(albedoChannelDef);

// Đặt opacity và blend mode cho layer mới
var layer = channel.Layers[channel.Layers.Count - 1];
layer.Opacity = 0.8f;
layer.ColorBlendMode = ColorBlendMode.Multiply;

// Đánh dấu channel dirty để kích hoạt re-composition
channel.SetDirty();

Toggling Layer Visibility

// Ẩn/hiện layer — tự động trigger re-composition
var layer = channel.Layers[0];
layer.IsVisible = !layer.IsVisible;

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