Add BlRoundedPolygonGeometry

- tests needed
- containsPoint: is not precise
- we should cache some calculated values, to avoid repeating the same maths on every new frame
- this is the closed polygon, it's a pity we don't support being an open geometry (a "polyline")
- we may decide to do some refactorings such as merge it with it's superclass

src/Bloc-Alexandrie/BlRoundedPolygonGeometry.extension.st

@@ -0,0 +1,79 @@
+Extension { #name : #BlRoundedPolygonGeometry }
+
+{ #category : #'*Bloc-Alexandrie' }
+BlRoundedPolygonGeometry >> aeApplyTo: aeCanvas element: aBlElement [
+
+	aeCanvas pathFactory: [ :cairoContext |
+		| p1 p2 p3 |
+		1 to: vertices size do: [ :i |
+			p1 := vertices at: i.
+			p2 := vertices atWrap: i + 1.
+			p3 := vertices atWrap: i + 2.
+			self
+				aeApplyTo: cairoContext
+				roundedCornerP1: p1
+				p2: p2
+				p3: p3 ].
+
+		cairoContext closePath ]
+]
+
+{ #category : #'*Bloc-Alexandrie' }
+BlRoundedPolygonGeometry >> aeApplyTo: cairoContext roundedCornerP1: p1 p2: p2 p3: p3 [
+	"Based on `RSAthensRenderer>>#applyRadius:on:from:to:`, which is based on
+	https://riptutorial.com/html5-canvas/example/18766/render-a-rounded-polygon-"
+
+	| v1 len1 a1 v2 len2 a2 sinA sin90 angle radDir isClockwise halfAngle cRadius lenOut p a b |
+	(p1 = p2 or: [ p2 = p3 ]) ifTrue: [ ^ self ].
+
+	v1 := p1 - p2.
+	len1 := ((v1 x * v1 x) + (v1 y * v1 y)) sqrt.
+	v1 := v1 / len1.
+	a1 := v1 angle.
+
+	v2 := p3 - p2.
+	len2 := ((v2 x * v2 x) + (v2 y * v2 y)) sqrt.
+	v2 := v2 / len2.
+	a2 := v2 angle.
+
+	sinA := (v1 x * v2 y) - (v1 y * v2 x).
+	sin90 := (v1 x * v2 x) - (v1 y * v2 y negated).
+	angle := sinA arcSin.
+	radDir := 1.
+	isClockwise := true.
+
+	sin90 < 0.0
+		ifTrue: [
+			angle < 0.0
+				ifTrue: [ angle := angle + Float pi ]
+				ifFalse: [
+					angle := angle - Float pi.
+					radDir := -1.
+					isClockwise := false ] ]
+		ifFalse: [
+			angle >= 0.0 ifTrue: [
+				radDir := -1.
+				isClockwise := false ] ].
+
+	halfAngle := angle / 2.0.
+	sinA :=  halfAngle sin.
+	lenOut := (sinA closeTo: 0.0)
+		ifTrue: [ Float infinity ]
+		ifFalse: [ (halfAngle cos * radius / sinA) abs ].
+	cRadius := radius.
+	lenOut > ((len1 / 2.0) min: (len2 / 2.0)) ifTrue: [
+		lenOut := (len1 / 2.0) min: (len2 / 2.0).
+		cRadius := (lenOut * halfAngle tan) abs ].
+
+	p := p2 + (v2 * lenOut) + (v2 y negated@ v2 x * cRadius * radDir).
+	a := a1 + (Float halfPi * radDir).
+	b := a2 - (Float halfPi * radDir).
+	(a closeTo: b) ifTrue: [ a := b ].
+
+	cairoContext
+		arcCenter: p
+		radius: cRadius
+		startAngle: a
+		endAngle: b
+		cw: isClockwise
+]

src/Bloc/BlRoundedPolygonGeometry.class.st

@@ -0,0 +1,32 @@
+"
+I represent a polygon with rounded corners. The arc is indicated by the radius (same radius for all corners).
+"
+Class {
+	#name : #BlRoundedPolygonGeometry,
+	#superclass : #BlPolygonGeometry,
+	#instVars : [
+		'radius'
+	],
+	#category : #'Bloc-Basic-Geometry'
+}
+
+{ #category : #'instance creation' }
+BlRoundedPolygonGeometry class >> vertices: aCollection radius: aNumber [
+
+	^ self new
+		vertices: aCollection;
+		radius: aNumber;
+		yourself
+]
+
+{ #category : #accessing }
+BlRoundedPolygonGeometry >> radius [
+
+	^ radius
+]
+
+{ #category : #accessing }
+BlRoundedPolygonGeometry >> radius: anInteger [
+
+	radius := anInteger
+]