Expand selection outline for single-selected draw shape (#1379)

Expand the selection outline on draw shapes according to pen thickness
when only one shape is selected.

![Kapture 2023-05-15 at 16 20
01](https://github.com/tldraw/tldraw/assets/1489520/373f0ec1-f43d-46c9-9729-0c84aaf2564b)

Right now the outline of many of our shapes don't take stroke thickness
into account. This is a pretty hard thing to get right, so in the short
term here's a fix for one of the most common places this is an issue:
selecting a single horizontal/vertical draw shape. This fix isn't
perfect: resizing gets slightly janky when you completely flip the shape
- see how the handle leaves the cursor behind in the gif when that
happens. We can revisit with a more comprehensive solution later.

This is pulled out from the highlighter work! The highlighter shape will
use the shape APIs added here.

### Change Type

- [x] `patch` — Bug Fix

### Test Plan

1. Create a draw shape
2. Select it
3. Selection bounds should include the stroke width
4. Add another shape to the selection
5. Selection bounds should no longer include the stroke width

### Release Notes

- Improve selection outlines around horizontal or vertical draw shapes

packages/editor/api-report.md

@@ -1864,6 +1864,8 @@ export class TLDrawUtil extends TLShapeUtil<TLDrawShape> {
     // (undocumented)
     defaultProps(): TLDrawShape['props'];
     // (undocumented)
+    expandSelectionOutlinePx(shape: TLDrawShape): number;
+    // (undocumented)
     getBounds(shape: TLDrawShape): Box2d;
     // (undocumented)
     getCenter(shape: TLDrawShape): Vec2d;
@@ -2513,6 +2515,8 @@ export abstract class TLShapeUtil<T extends TLUnknownShape> {
     canUnmount: TLShapeUtilFlag<T>;
     center(shape: T): Vec2dModel;
     abstract defaultProps(): T['props'];
+    // @internal (undocumented)
+    expandSelectionOutlinePx(shape: T): number;
     protected abstract getBounds(shape: T): Box2d;
     abstract getCenter(shape: T): Vec2dModel;
     getEditingBounds: (shape: T) => Box2d;

packages/editor/src/lib/app/shapeutils/TLDrawUtil/TLDrawUtil.tsx

@@ -303,6 +303,11 @@ export class TLDrawUtil extends TLShapeUtil<TLDrawShape> {
 			},
 		}
 	}
+
+	expandSelectionOutlinePx(shape: TLDrawShape): number {
+		const multiplier = shape.props.dash === 'draw' ? 1.6 : 1
+		return (this.app.getStrokeWidth(shape.props.size) * multiplier) / 2
+	}
 }
 
 /** @public */

packages/editor/src/lib/app/shapeutils/TLShapeUtil.ts

@@ -369,6 +369,11 @@ export abstract class TLShapeUtil<T extends TLUnknownShape> {
 		return false
 	}
 
+	/** @internal */
+	expandSelectionOutlinePx(shape: T): number {
+		return 0
+	}
+
 	//  Events
 
 	/**

packages/editor/src/lib/components/SelectionFg.tsx

@@ -25,14 +25,24 @@ export const SelectionFg = track(function SelectionFg() {
 	const isDefaultCursor = !app.isMenuOpen && app.cursor.type === 'default'
 	const isCoarsePointer = app.isCoarsePointer
 
-	const bounds = app.selectionBounds
+	let bounds = app.selectionBounds
+	const shapes = app.selectedShapes
+	const onlyShape = shapes.length === 1 ? shapes[0] : null
 
-	useTransform(rSvg, bounds?.x, bounds?.y, 1, app.selectionRotation)
+	// if all shapes have an expandBy for the selection outline, we can expand by the l
+	const expandOutlineBy = onlyShape
+		? app.getShapeUtil(onlyShape).expandSelectionOutlinePx(onlyShape)
+		: 0
+
+	useTransform(rSvg, bounds?.x, bounds?.y, 1, app.selectionRotation, {
+		x: -expandOutlineBy,
+		y: -expandOutlineBy,
+	})
 
 	if (!bounds) return null
+	bounds = bounds.clone().expandBy(expandOutlineBy)
 
 	const zoom = app.zoomLevel
-	const shapes = app.selectedShapes
 	const rotation = app.selectionRotation
 	const isChangingStyles = app.isChangingStyle
 
@@ -54,8 +64,6 @@ export const SelectionFg = track(function SelectionFg() {
 	const targetSizeX = (isSmallX ? targetSize / 2 : targetSize) * (mobileHandleMultiplier * 0.75)
 	const targetSizeY = (isSmallY ? targetSize / 2 : targetSize) * (mobileHandleMultiplier * 0.75)
 
-	const onlyShape = shapes.length === 1 ? shapes[0] : null
-
 	const showSelectionBounds =
 		(onlyShape ? !app.getShapeUtil(onlyShape).hideSelectionBoundsFg(onlyShape) : true) &&
 		!isChangingStyles

packages/editor/src/lib/hooks/useTransform.ts

@@ -1,3 +1,4 @@
+import { VecLike } from '@tldraw/primitives'
 import { useLayoutEffect } from 'react'
 
 export function useTransform(
@@ -5,21 +6,24 @@ export function useTransform(
 	x?: number,
 	y?: number,
 	scale?: number,
-	rotate?: number
+	rotate?: number,
+	additionalOffset?: VecLike
 ) {
 	useLayoutEffect(() => {
 		const elm = ref.current
 		if (!elm) return
 		if (x === undefined) return
 
+		let trans = `translate(${x}px, ${y}px)`
 		if (scale !== undefined) {
+			trans += ` scale(${scale})`
+		}
 		if (rotate !== undefined) {
-				elm.style.transform = `translate(${x}px, ${y}px) scale(${scale}) rotate(${rotate}rad)`
-			} else {
-				elm.style.transform = `translate(${x}px, ${y}px) scale(${scale})`
+			trans += ` rotate(${rotate}rad)`
 		}
-		} else {
-			elm.style.transform = `translate(${x}px, ${y}px)`
+		if (additionalOffset) {
+			trans += ` translate(${additionalOffset.x}px, ${additionalOffset.y}px)`
 		}
+		elm.style.transform = trans
 	})
 }