CanvasView: optimize rendering (#64)

- Only re-draw elements that are inside the dirtyRect.

  previously for each dirty rect I re-rendered the whole set of concepts.

- Mark view as opaque

  so the OS doesn’t need to render views under.

LinkedIdeas/CanvasView.swift

@@ -10,10 +10,13 @@ import Cocoa
 
 public protocol CanvasViewDataSource {
   var drawableElements: [DrawableElement] { get }
+
+  func drawableElements(forRect: NSRect) -> [DrawableElement]
 }
 
 public class CanvasView: NSView {
 
+  public override var isOpaque: Bool { return true }
   public var dataSource: CanvasViewDataSource?
 
   var selectFromPoint: NSPoint?
@@ -34,20 +37,23 @@ public class CanvasView: NSView {
 
   override public func draw(_ dirtyRect: NSRect) {
     super.draw(dirtyRect)
-    drawBackground()
+    drawBackground(dirtyRect)
+    drawElements(inRect: dirtyRect)
+    drawSelectionRect()
+    drawLinkConstructionArrow()
+  }
 
-    if let dataSource = dataSource {
-      for element in dataSource.drawableElements { element.draw() }
+  func drawElements(inRect dirtyRect: NSRect) {
+    guard let dataSource = dataSource else {
+      return
     }
 
-    drawSelectionRect()
-
-    drawLinkConstructionArrow()
+    dataSource.drawableElements(forRect: dirtyRect).forEach({ $0.draw() })
   }
 
-  func drawBackground() {
+  func drawBackground(_ dirtyRect: NSRect) {
     NSColor.white.set()
-    NSRectFill(bounds)
+    NSRectFill(dirtyRect)
   }
 
   func drawSelectionRect() {
@@ -57,7 +63,6 @@ public class CanvasView: NSView {
 
     let borderColor = NSColor(red: 0, green: 0, blue: 1, alpha: 1)
     let backgroundColor = NSColor(red: 0, green: 0, blue: 1, alpha: 0.5)
-
     let bezierPath = NSBezierPath(rect: selectionRect)
 
     borderColor.set()

LinkedIdeas/CanvasViewController+CanvasViewDataSource.swift

@@ -24,4 +24,8 @@ extension CanvasViewController: CanvasViewDataSource {
 
     return elements
   }
+
+  func drawableElements(forRect containerRect: NSRect) -> [DrawableElement] {
+    return drawableElements.filter({ containerRect.intersects($0.drawingBounds) })
+  }
 }

LinkedIdeas/CanvasViewController+DraggingActions.swift

@@ -120,6 +120,6 @@ extension CanvasViewController {
     dragCount = 0
     canvasView.selectFromPoint = nil
     canvasView.selectToPoint = nil
-    canvasView.needsDisplay = true
+    reRenderCanvasView()
   }
 }

LinkedIdeas/Document.swift

@@ -194,6 +194,10 @@ extension Document: LinkedIdeasDocument {
 }
 
 extension Document: CanvasViewDataSource {
+  public func drawableElements(forRect: NSRect) -> [DrawableElement] {
+    return drawableElements
+  }
+
   public var drawableElements: [DrawableElement] {
     var elements: [DrawableElement] = []