> For the complete documentation index, see [llms.txt](https://viridian-games.gitbook.io/pixel-palette/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://viridian-games.gitbook.io/pixel-palette/core-components/brush-system.md).

# Brush System

**`IBrush` interface** — every tool implements `StrokeStart()`, `StrokeMove()`, `StrokeEnd()`. The input handler calls these as the user clicks, drags, and releases.

**`BrushSystem`** manages tool switching and brush size (1–16). It creates the right `IBrush` instance when you select a tool:

<table><thead><tr><th width="155">Tool</th><th width="257.333251953125">Class</th><th>What it does</th></tr></thead><tbody><tr><td><strong>Pen</strong></td><td><code>PixelPenBrush</code></td><td>Paints a square of pixels at brush size using the current pen color</td></tr><tr><td><strong>Eraser</strong></td><td><code>PixelPenBrush</code> (same class)</td><td>Same square, but writes transparent black (alpha=0) instead of the pen color. Detected by checking <code>brushSystem.CurrentBrushType == BrushType.Eraser</code></td></tr><tr><td><strong>Fill</strong></td><td><code>PixelFillBrush</code></td><td>Flood-fill from the clicked pixel using a radial queue (Burst-compiled). Replaces all connected pixels of the same color</td></tr><tr><td><strong>Color Picker</strong></td><td><code>ColorPickerBrush</code></td><td>Samples the pixel under the cursor and sets the pen color to match. No pixels are changed</td></tr><tr><td><strong>Select</strong></td><td><code>SelectionBrush</code></td><td>Creates a rectangular selection. Used by the selection manager for cut/copy/move/delete</td></tr></tbody></table>

**Pen & Eraser details:**

* `PaintPixelSquare(center, size)` — writes to the layer's `RawPixels` array directly, then uploads that region to the GPU via `Texture.SetPixels32()`
* Between strokes, draws Bresenham lines between consecutive pixels for smooth lines at any brush size
* **Quick shapes** — hold still for 1.5 seconds. The brush detects if the stroke looks like a line or an ellipse. Once detected, it switches to shape mode: the stroke restores original pixels, then redraws the shape preview (line, ellipse, or rectangle) from the anchor point. Toggle between ellipse/rectangle, or hold Shift for perfect aspect ratio

**Fill brush** uses a `NativeQueue` + `NativeList` for high-performance flood fill (Burst-compiled). It expands outward from the click point, replacing all connected pixels of the target color with the pen color. (Procreate anyone?)


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