Do a quick round of optimizations

Fixes #13.

frosty.go

@@ -11,6 +11,8 @@ import (
 	"os"
 	"regexp"
 	"runtime"
+
+	"github.com/pkg/profile"
 )
 
 func jsonError(raw []byte, err error) error {
@@ -47,10 +49,15 @@ func main() {
 		supersampling = flag.Int("supersampling", 1, "Supersampling (antialiasing) factor")
 		// Default value of 4 * numcpu is based on some ad hoc testing.
 		parallelism = flag.Int("parallelism", 4*runtime.NumCPU(), "Number of rays to compute in parallel")
+		cpuProfile  = flag.Bool("cpuprofile", false, "Emit CPU profile")
 	)
 	flag.Parse()
 	_ = *debug
 
+	if *cpuProfile {
+		defer profile.Start(profile.CPUProfile).Stop()
+	}
+
 	if *supersampling < 1 || *supersampling > 8 {
 		log.Fatalf("Supersampling should be between 1 and 8; got %d", *supersampling)
 	}

image.go

@@ -28,12 +28,19 @@ func (i *Image) At(x, y int) Color {
 }
 
 func (i *Image) Set(x, y int, c Color) {
-	if x < 0 || x >= i.Width || y < 0 || y >= i.Height {
-		panic("Out of bounds for Set() on Image.")
-	}
+	//if x < 0 || x >= i.Width || y < 0 || y >= i.Height {
+	//        panic("Out of bounds for Set() on Image.")
+	//}
 	i.Pix[y*i.Width+x] = c
 }
 
+func (i *Image) SetLine(y int, c []Color) {
+	if len(c) != i.Width {
+		panic("line of wrong length")
+	}
+	copy(i.Pix[y*i.Width:], c)
+}
+
 // ToneMap scales down the range of colors to 32-bit RGBA. Right now it uses a
 // simplistic heuristic: it just scales the values linearly such that the most
 // intense channel value is 0xFF.

make.sh

@@ -5,5 +5,6 @@ set -eu -o pipefail
 go build -o frosty
 time ./frosty \
   -debug \
+  -cpuprofile \
   -hpixels 1200 \
   -out out.png

render.go

@@ -15,16 +15,17 @@ func (r *Rendering) Render(parallelism int) *Image {
 	h := int(float64(w) * r.Camera.Aspect)
 	img := NewImage(w, h)
 	scanner := NewLineScanner(r.Camera, r.HPixels)
-
 	var wg sync.WaitGroup
 	wg.Add(parallelism)
 	lines := scanner.Scan()
 	for i := 0; i < parallelism; i++ {
 		go func() {
+			result := make([]Color, scanner.hPixels)
 			for line := range lines {
 				for x := line.xMin; x < line.xMax; x++ {
-					img.Set(x, line.y, r.Trace(line.rays[x]))
+					result[x] = r.Trace(line.rays[x])
 				}
+				img.SetLine(line.y, result)
 			}
 			wg.Done()
 		}()