#2: Implement Arc Demo, fixes for path construction

- fixed the bug where appending an arc wouldn't have changed the path's current position
- changed the assert condition for path construction (decreased accuracy)
- .black, .white and .clear colors are now in .deviceGray color space

Demo/ArcDemo.playground/Contents.swift

@@ -0,0 +1,90 @@
+import SwiftyHaru
+
+let document = PDFDocument()
+let page = document.addPage(width: 200, height: 220)
+
+// Draw the grid
+
+let horizontalLabels = stride(from: 50, through: 150, by: 50).map(String.init)
+let verticalLabels = stride(from: 10, through: 210, by: 10).map(String.init)
+
+let labels = Grid.Labels(top: Grid.LabelParameters(sequence: "" + horizontalLabels,
+                                                   offset: Vector(x: 0, y: -6)),
+                         bottom: Grid.LabelParameters(sequence: "" + horizontalLabels,
+                                                      offset: Vector(x: 0, y: 6)),
+                         left: Grid.LabelParameters(sequence: "" + verticalLabels,
+                                                    frequency: 1,
+                                                    offset: Vector(x: 6, y: 0)))
+
+let serifs = Grid.Serifs(top: .default,
+                         bottom: .default,
+                         left: Grid.SerifParameters(frequency: 1),
+                         right: nil)
+
+let grid = Grid(width: page.width, height: page.height, labels: labels, serifs: serifs)
+page.draw(object: grid, position: .zero)
+
+/* Draw pie chart
+ *
+ *   a: 45% Red
+ *   b: 25% Blue
+ *   c: 15% green
+ *   d: other yellow
+ */
+
+let center = Point(x: 100, y: 100)
+
+var temporaryPosition: Point
+
+var a = Path()
+    .moving(to: center)
+    .appendingLine(toX: 100, y: 180)
+    .appendingArc(center: center,
+                  radius: 80,
+                  beginningAngle: 0,
+                  endAngle: 360 * 0.45)
+temporaryPosition = a.currentPosition
+a.appendLine(to: center)
+
+var b = Path()
+    .moving(to: center)
+    .appendingLine(to: temporaryPosition)
+    .appendingArc(center: center, radius: 80, beginningAngle: 360 * 0.45, endAngle: 360 * 0.7)
+temporaryPosition = b.currentPosition
+b.appendLine(to: center)
+
+var c = Path()
+    .moving(to: center)
+    .appendingLine(to: temporaryPosition)
+    .appendingArc(center: center, radius: 80, beginningAngle: 360 * 0.7, endAngle: 360 * 0.85)
+temporaryPosition = c.currentPosition
+c.appendLine(to: center)
+
+var d = Path()
+    .moving(to: center)
+    .appendingLine(to: temporaryPosition)
+    .appendingArc(center: center, radius: 80, beginningAngle: 360 * 0.85, endAngle: 360)
+    .appendingLine(to: center)
+
+// Draw center circle
+let centerCircle = Path().appendingCircle(center: center, radius: 30)
+
+page.draw { context in
+
+    context.fillColor = #colorLiteral(red: 0.9254902005, green: 0.2352941185, blue: 0.1019607857, alpha: 1)
+    context.fill(a)
+
+    context.fillColor = #colorLiteral(red: 0.2196078449, green: 0.007843137719, blue: 0.8549019694, alpha: 1)
+    context.fill(b)
+
+    context.fillColor = #colorLiteral(red: 0.4666666687, green: 0.7647058964, blue: 0.2666666806, alpha: 1)
+    context.fill(c)
+
+    context.fillColor = #colorLiteral(red: 0.9686274529, green: 0.78039217, blue: 0.3450980484, alpha: 1)
+    context.fill(d)
+
+    context.fillColor = .white
+    context.fill(centerCircle)
+}
+
+document.display()

Demo/ArcDemo.playground/Sources/ViewConfiguration.swift

@@ -0,0 +1,17 @@
+import Quartz
+import PlaygroundSupport
+import SwiftyHaru
+
+public extension SwiftyHaru.PDFDocument {
+
+    public func display() {
+
+        let view = PDFView(frame: NSRect(x: 0, y: 0, width: 480, height: 640))
+
+        view.document = PDFDocument(data: getData())
+
+        view.scaleFactor = 0.75
+
+        PlaygroundPage.current.liveView = view
+    }
+}

Demo/ArcDemo.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Sources/SwiftyHaru/Color.swift

@@ -24,14 +24,14 @@ public struct Color {
     /// Returns the blue color in `PDFColorSpace.deviceRGB` space
     public static let blue = Color(red: 0, green: 0, blue: 1)!
 
-    /// Returns the black color in `PDFColorSpace.deviceRGB` space
-    public static let black = Color(red: 0, green: 0, blue: 0)!
+    /// Returns the black color in `PDFColorSpace.deviceGray` space
+    public static let black = Color(gray: 0)!
 
-    /// Returns the white color in `PDFColorSpace.deviceRGB` space
-    public static let white = Color(red: 1, green: 1, blue: 1)!
+    /// Returns the white color in `PDFColorSpace.deviceGray` space
+    public static let white = Color(gray: 1)!
 
-    /// Returns the transparent white color in `PDFColorSpace.deviceRGB` space
-    public static let clear = Color(red: 1, green: 1, blue: 1, alpha: 0)!
+    /// Returns the transparent white color in `PDFColorSpace.deviceGray` space
+    public static let clear = Color(gray: 1, alpha: 0)!
 
     internal enum _ColorSpaceWrapper {
         case rgb(red: Float, green: Float, blue: Float)

Sources/SwiftyHaru/DrawingContext.swift

@@ -230,7 +230,11 @@ public final class DrawingContext {
             }
         }
 
-        assert(path.currentPosition == Point(HPDF_Page_GetCurrentPos(_page)))
+        assert(path.currentPosition.x - HPDF_Page_GetCurrentPos(_page).x < 0.001 &&
+               path.currentPosition.y - HPDF_Page_GetCurrentPos(_page).y < 0.001,
+               "The value of property `currentPosition` (\(path.currentPosition)) is not equal to " +
+               "the value returned from the function " +
+               "`HPDF_Page_GetCurrentPos` (\(HPDF_Page_GetCurrentPos(_page)))")
 
         HPDF_Page_MoveTo(_page, 0, 0)
     }

Sources/SwiftyHaru/Path.swift

@@ -6,6 +6,8 @@
 //
 //
 
+import CoreFoundation
+
 /// A type for graphics paths: mathematical descriptions of shapes or lines to be drawn in a `DrawingContext`.
 public struct Path {
 
@@ -162,6 +164,15 @@ public struct Path {
 
         guard endAngle > beginningAngle else { return }
 
+        let deltaAngle = (90 - (beginningAngle + endAngle) / 2) / 180 * Float.pi
+        let newAngle = (endAngle - beginningAngle) / 2 / 180 * Float.pi
+
+        let rx3 = radius * cos(newAngle)
+        let ry3 = -radius * sin(newAngle)
+
+        _currentPosition = Point(x: rx3 * cos(deltaAngle) - ry3 * sin(deltaAngle) + center.x,
+                                 y: rx3 * sin(deltaAngle) + ry3 * cos(deltaAngle) + center.y)
+
         _pathConstructionSequence.append(.arc(center: center,
                                               radius: radius,
                                               beginningAngle: beginningAngle,