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# Input System

Two components work together: **CanvasInputHandler** reads input devices, and **CanvasViewController** applies zoom/pan to the canvas RectTransform.

#### Input Priority (Update order)

Each frame, `CanvasInputHandler.Update()` checks input in this order:

1. **Keyboard** — brush cycling (E), undo (Ctrl+Z), redo (Ctrl+Y), quick-shape toggle (Ctrl), delete selection (Del)
2. **Touch pinch/zoom** — two-finger pan + pinch zoom. Tracks `hasSeenMultiTouch` to suppress single-touch drawing during pinch
3. **Mouse scroll zoom** — scroll wheel zooms at the cursor position (1.1x factor)
4. **Mouse pan** — right-click or middle-click drag pans the canvas. Sets a 2-frame cooldown to avoid drawing immediately after panning
5. **Drawing** — if nothing else consumed the frame, process pen/touch/mouse strokes

#### Drawing Flow

```
TryGetDrawingInput()  →  gets screen position + pressure from Pen, Touch, or Mouse (priority order)
       ↓
TryScreenToPixel()    →  converts screen coords to pixel coords on the canvas
       ↓
HandleDrawing()       →  starts, continues, or ends a stroke via canvas.StartStroke/ContinueStroke/EndStroke
```

**Stroke start** — records the pixel, sets up quick-shape timers, starts undo capture

**Stroke move** — for Pen tool: if the pointer stays still (<4px movement for 0.25s), activates **quick-shape mode** (detects if stroke looks like a line or ellipse and switches to shape preview). Otherwise, draws Bresenham-interpolated pixels between the last and current position.

**Stroke end** — finalizes undo capture, cleans up quick-shape state

**Selection move** — if you click inside an existing selection with a non-select tool, it starts dragging the selection content instead of drawing.

**Double-tap** — within 0.3s / 20px of the last tap, toggles quick-shape between ellipse and rectangle.

#### UI Detection

`IsOverUI` = `IsOverUITK || IsOverUGUI`. When true, drawing is suppressed. The UITK controller tracks pointer enter/leave with a counter, and the uGUI controller runs `EventSystem.RaycastAll` each frame to set `IsOverUGUI`.

#### Canvas Input Utilities

* **`TryScreenToPixel(camera, screenPos, out pixelPos)`** — uses `RectTransformUtility.ScreenPointToLocalPointInRectangle` on the inputRect, then normalizes to pixel coords. Returns false if outside canvas bounds.
* **`ResolveEventCamera()`** — returns null for ScreenSpace-Overlay canvases, the world camera for ScreenSpace-Camera, or Camera.main as fallback.

#### Canvas View Controller

* **Zoom(factor, screenPivot, camera)** — multiplies current zoom (clamped 0.25x–16x), applies to `canvasRect.localScale`, adjusts `anchoredPosition` so the pivot point stays fixed on screen. Fires `OnZoomChanged`.
* **Pan(delta)** — adds delta to `canvasRect.anchoredPosition`. Fires `OnPanChanged`.
* **ResetView()** — resets zoom to 1x and position to center.


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