Hide blob in 2D example if user hasn't clicked in awhile

examples/canvas/main.go

@@ -8,81 +8,129 @@ import (
 )
 
 const (
-	width   = 1024
-	height  = 768
-	fps     = 60
-	bgColor = "#111111"
+	canvasWidth  = 1024
+	canvasHeight = 768
+	fps          = 60
+	circleRadius = 100
+	bgColor      = "#111111"
+	idleTimeout  = time.Second * 5
+)
+
+type State int
+
+const (
+	unstarted State = iota
+	running
+	timeout
 )
 
 func main() {
 	var (
-		circ       = newCircle()
-		clickedYet bool
+		circ      Circle
+		state     State
+		lastClick time.Time
 	)
 
 	c := canvas.NewCanvas(&canvas.CanvasConfig{
-		Width:     width,
-		Height:    height,
+		Width:     canvasWidth,
+		Height:    canvasHeight,
 		FrameRate: fps,
 		Title:     "Harmonica",
 	})
 
 	c.Draw(func(ctx *canvas.Context) {
-		ctx.SetHexColor(bgColor)
 		ctx.Clear()
+		ctx.SetHexColor(bgColor)
 
-		if ctx.IsMouseDragged {
-			if !clickedYet {
-				// Set starting positions.
-				circ.x = ctx.Mouse.X
-				circ.y = ctx.Mouse.Y
+		switch state {
+		case unstarted:
+			if ctx.IsMouseDragged {
+				const frequency = 0.8
+				const damping = 1.0
 
-				circ.Radius = 100
-				clickedYet = true
+				circ = Circle{
+					// Setup a new spring.
+					spring: harmonica.NewSpring(harmonica.TimeDelta(time.Second/fps), frequency, damping),
+
+					// Set target radius.
+					Radius: circleRadius,
+				}
+
+				// Set starting position.
+				circ.SetPos(ctx.Mouse.X, ctx.Mouse.Y)
+
+				lastClick = time.Now()
+				state = running
 			}
-			circ.X = ctx.Mouse.X
-			circ.Y = ctx.Mouse.Y
-		}
 
-		if clickedYet {
-			circ.draw(ctx)
+		case running:
+			if ctx.IsMouseDragged {
+				lastClick = time.Now()
+
+				if circ.Hidden {
+					circ.SetPos(ctx.Mouse.X, ctx.Mouse.Y)
+					circ.Hidden = false
+				}
+
+				// Update targets for our spring animation.
+				circ.X = ctx.Mouse.X
+				circ.Y = ctx.Mouse.Y
+				circ.Radius = circleRadius
+			}
+
+			circ.Draw(ctx)
+
+			if time.Now().After(lastClick.Add(idleTimeout)) {
+				state = timeout
+			}
+
+		case timeout:
+			circ.Radius = 0
+			circ.Draw(ctx)
+			if circ.rad == 0 {
+				state = running
+				lastClick = time.Now()
+			}
 		}
 	})
 }
 
-type circle struct {
-	// Target values. This is what the spring will seek.
+type Circle struct {
+	// Target values. This is what the spring will use as an equilibrium to
+	// animate towards.
 	X, Y, Radius float64
 
-	// Managed values. These are the initial
 	x, xVel     float64
 	y, yVel     float64
 	rad, radVel float64
+	spring      harmonica.Spring
 
-	spring harmonica.Spring
+	Hidden bool
 }
 
-func newCircle() circle {
-	const (
-		frequency = 0.8
-		damping   = 0.99
-	)
-
-	return circle{
-		spring: harmonica.NewSpring(harmonica.TimeDelta(time.Second/fps), frequency, damping),
-	}
+func (c *Circle) SetPos(x, y float64) {
+	c.x = x
+	c.y = y
+	c.Hidden = false
 }
 
-func (c *circle) draw(ctx *canvas.Context) {
-	// Update
+func (c *Circle) Draw(ctx *canvas.Context) {
+	// Update position and radius.
 	c.spring.Update(&c.x, &c.xVel, c.X)
 	c.spring.Update(&c.y, &c.yVel, c.Y)
 	c.spring.Update(&c.rad, &c.radVel, c.Radius)
 
+	if c.rad < 0 {
+		c.rad = 0
+		c.radVel = 0
+		c.Hidden = true
+	}
+
 	const color = "#f1f1f1"
 
 	ctx.Push()
 	ctx.DrawCircle(c.x, c.y, c.rad)
 	ctx.SetHexColor(color)
 	ctx.Fill()
+	ctx.Pop()
 }