Load Balance Collision and Actor Loop Across CPU Cores

* Add sync.WaitGroup to some parts of the level collision detection
  function and Canvas.Loop() to speed up the frame rate by load
  balancing some work in parallel across multiple cores.
* Improves FPS from 30 to 55+ even for busy scenes with lots of mobile
  enemies walking around.
* Before the level collision optimization, framerate would sometimes dip
  to 30 FPS simply to move the player character on a completely blank
  map!

cmd/doodle/main.go

@@ -26,6 +26,10 @@ func init() {
 	if BuildDate == "" {
 		BuildDate = time.Now().Format(time.RFC3339)
 	}
+
+	// Use all the CPU cores for collision detection and other load balanced
+	// goroutine work in the app.
+	runtime.GOMAXPROCS(runtime.NumCPU())
 }
 
 func main() {

pkg/collision/collide_level.go

@@ -1,6 +1,8 @@
 package collision
 
 import (
+	"sync"
+
 	"git.kirsle.net/apps/doodle/lib/render"
 	"git.kirsle.net/apps/doodle/pkg/doodads"
 	"git.kirsle.net/apps/doodle/pkg/level"
@@ -202,10 +204,34 @@ func (c *Collide) IsColliding() bool {
 func (c *Collide) ScanBoundingBox(box render.Rect, grid *level.Chunker) bool {
 	col := GetCollisionBox(box)
 
-	c.ScanGridLine(col.Top[0], col.Top[1], grid, Top)
-	c.ScanGridLine(col.Bottom[0], col.Bottom[1], grid, Bottom)
-	c.ScanGridLine(col.Left[0], col.Left[1], grid, Left)
-	c.ScanGridLine(col.Right[0], col.Right[1], grid, Right)
+	// Check all four edges of the box in parallel on different CPU cores.
+	type jobSide struct {
+		p1   render.Point
+		p2   render.Point
+		side Side
+	}
+	jobs := []jobSide{
+		jobSide{col.Top[0], col.Top[1], Top},
+		jobSide{col.Bottom[0], col.Bottom[1], Bottom},
+		jobSide{col.Left[0], col.Left[1], Left},
+		jobSide{col.Right[0], col.Right[1], Right},
+	}
+	var wg sync.WaitGroup
+	for _, job := range jobs {
+		wg.Add(1)
+		go func(job jobSide) {
+			defer wg.Done()
+			c.ScanGridLine(job.p1, job.p2, grid, job.side)
+		}(job)
+	}
+
+	wg.Wait()
+
+	// TODO: the old synchronous version of the above.
+	// c.ScanGridLine(col.Top[0], col.Top[1], grid, Top)
+	// c.ScanGridLine(col.Bottom[0], col.Bottom[1], grid, Bottom)
+	// c.ScanGridLine(col.Left[0], col.Left[1], grid, Left)
+	// c.ScanGridLine(col.Right[0], col.Right[1], grid, Right)
 	return c.IsColliding()
 }
 

pkg/uix/canvas.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"sync"
 	"time"
 
 	"git.kirsle.net/apps/doodle/lib/events"
@@ -191,7 +192,12 @@ func (w *Canvas) Loop(ev *events.State) error {
 	// Move any actors. As we iterate over all actors, track their bounding
 	// rectangles so we can later see if any pair of actors intersect each other.
 	boxes := make([]render.Rect, len(w.actors))
+	var wg sync.WaitGroup
 	for i, a := range w.actors {
+		wg.Add(1)
+		go func(i int, a *Actor) {
+			defer wg.Done()
+
 			// Advance any animations for this actor.
 			if a.activeAnimation != nil && a.activeAnimation.nextFrameAt.Before(now) {
 				if done := a.TickAnimation(a.activeAnimation); done {
@@ -214,7 +220,7 @@ func (w *Canvas) Loop(ev *events.State) error {
 			// If not moving, grab the bounding box right now.
 			if v == render.Origin {
 				boxes[i] = doodads.GetBoundingRect(a)
-			continue
+				return
 			}
 
 			// Create a delta point from their current location to where they
@@ -237,6 +243,8 @@ func (w *Canvas) Loop(ev *events.State) error {
 
 			// Store this actor's bounding box after they've moved.
 			boxes[i] = doodads.GetBoundingRect(a)
+		}(i, a)
+		wg.Wait()
 	}
 
 	// Check collisions between actors.